My P0089 (P310B) PITA

[raerwin72]

Fix:
Short version is the 5V Vcc wire was cut in the engine harness between the firewall and timing chain cover. Long version is in a separate post down below.

What I've personally replaced:
- LPFP
- OEM Fuel filter
- OEM low pressure fuel sensor
- OEM HPFP and follower

What I've personally lost:
- Time
- Money
- Sanity


Alright, I'm going to swallow my pride and ask the experts here for help on this issue. I've done my research, and I'm fully aware that this pesky P0089 code has been discussed in detail several times over, but my problem persists after taking the recommended actions suggested to all those before me. I would really appreciate additional insight on this issue. I will spill my life's story since I bought the car to fill you all in on what was done and why. I don't mind driving a car with a CEL as long as I know the EXACT cause, but I don't want to cause any extra damage to the parts I replaced from not knowing what's actually wrong.

For background, the money pit in question is a 2007 A4 2.0t quattro 6-spd that I bought from my friend, who bought from some other guy so the service background is pretty limited. I do know that the cam follower was inspected and replaced by the PO less than an oil change ago before I bought it, with no abnormal signs of wear to the follower or cam. I bought the car knowing about the P code, but it drove fine with no misfires, stutters or hiccups so I figured it'd be alright since the cam follower checked out. I've never driven an FSI quattro before so I guess I have nothing to compare it to for acceleration, but considering the power to weight it seemed to check out to me. When I finally got around to using my buddy's VAGCOM for diagnosis (sorry I only have a crappy csv file that I don't know how to link), I was noticing that the group 103 "Current - Fuel Pressure" and "Fuel Pressure - Regulator" values were pretty rock steady at 3.93 bar and 4000 respectively, and the 106 "Electric Fuel - Pump 1/2" was fluctuating at idle in the 80's%. The "Fuel Rail - Pressure (actual)" however was at 50 bar and would increase with engine load and rpm as I would expect, ~100 bar on acceleration before I would shift (keeping it below 3k rpms).

Originally the high duty cycle with poor low pressure led me to believe that the LPFP and or filter were bad and at 200k miles it wouldn't be bad to replace and check condition of tank/pump. I replaced the pump, filter, and inspected the tank and saw now crud or buildup. Cleared the code, drove to fill the tank back up and sure enough the CEL came back on my way home. I then figured the G410 sensor would be the culprit and replaced that with a brand new rev k from ECS tuning. Installed it, cleared the code, drove around and the light came back. Decided to grab my buddy's VAGCOM again and see if anything changed. The 103 "Current - Fuel Pressure" actually went down slightly to 3.2 bar or so and the other values remained the same as before.

At this point I was furious. I read here that someone had a problem with the pressure relief valve being stuck open so I looked at fuel pressure with a hot engine just after IG off and back on again. I was seeing pressures at the fuel rail rise from 50 bar up to 110 bar until I decided there was no real pressure leaks on the high side.

This led me to believe that the pressure regulator module on the HPFP could be stuck or faulty or something so I replaced the HPFP with a new one. when I finally installed the new pump and cleared the code the car felt great. Ran fine and the the placebo affect made me think that I gained more HP. Unfortunately the CEL came back at the same exact point on my way back from the gas station as before, and I nearly punched a hole in my dash I was so upset. More money down the hole and the VAGCOM came back with the EXACT same 103 and 106 values as before. To note, I monitored the group 230 to check specified and actual rail pressures and the actual pressure never deviated more than a bar or two from specified.

It's at this point I decided to do so some electrical testing on the new G410 sensor and connector from the ECU in order to know exactly why I kept seeing a rock steady, with maybe +/- 0.01 bar, reading from this sensor. I found that the connector has a good 4.9V Vcc reading with reference to both battery ground and signal ground while the sensor is unplugged. I measured resistance of the signal ground to battery ground and it's about 7 ohms so I figured I don't have any open circuits, or poor grounding between connector and ECU. I moved on to making a harness that would let me plug the sensor into the connector, and measure each wire individually, while the engine is running. This is where I though things got interesting.

With the sensor plugged in, and the engine running, I was reading 1.6V at Vcc, 1.1V at signal, and 0V at ground. I decided to see if the old sensor was any different while just measuring atmospheric pressure. Plugged it in without being screwed into the HPFP and sure enough, relatively same voltages. I disconnected the engine harness connector from the sensor and the Vcc went back up to 5V. I thought this was odd and was curious to see if plugging in the old sensor would show an atmospheric pressure if I left it dangling in the air, but no... 3.82 bar on VCDS. So I am thinking this MUST be an electrical issue. Either an issue with the sensors or ECU internally since neither sensor moved from the ~3bar reading regardless of actual pressure at the sensor. Thinking it was the ECU supply voltage, I took a 5 volt known supply and fed it to the sensor to measure the output voltage. In ambient it was around 4.5V or so... I honestly cant remember, but the pressure reading at the ECU detected the same as when the connector is unplugged (super strange I think).

I was fiddling around with a potentiometer and the 5V power supply to try and trick the ECU into thinking there was a good sensor, and was able to get a reading of 5-6 bar (which would finally fluctuate with accel pedal input). This dropped the LPFP duty cycle down to 50%, but when I inspected my wiring I noticed I was feeding the signal line with 5V and the Vcc line was at 1.6V or so. Thinking the wiring in the engine harness got swapped (has happened to me on other projects), I swapped power and signal to the sensor but the ECU basically detected an open/short condition so I really don't know what could be wrong. A combination of being tired, poor lighting, and hunger made me cut the testing short that night.

My question becomes this... what are the odds of having two bad sensors or a bad ECU? I don't have another running FSI engine at my disposal for me to do similar electrical tests on to see what the typical characteristics are for this particular sensor. So I was wondering if anyone had any insight before I drop even more money on an ECU, a trip to the dealer to have immobi registered, VIN written, and to have it potentially have the same or more P codes. I would be inclined to believe that this sensor should have a constant 5V Vcc even while plugged in, but without knowing the characteristics of this particular pressure sensor, I have no idea what the typical behavior should be, if the ECU is measuring absolute voltage, or a differential to determine the low fuel pressure.

I have not been able to get at the ECU or the fuses/relays that might be under the plastic ECU cover to check for corrosion, but the car was from Alabama so I doubt there would be anything, let alone something causing an electrical fault on just this one sensor exclusively. I will check though to rule it out. I haven't replaced the fuel pump controller because I was able to get the duty cycle down when I was messing with voltages to the ECU, and I haven't done a fuel pressure test with a mechanical gauge because if the ECU was reading the sensor correctly I would expect the pressure to fluctuate by more than 0.01 bar whilst I spank the accelerator pedal to show it who's boss. If it turns out that someone can attest to voltages of ~1.6V Vcc while plugged in to a working sensor, then I will try a pressure test and drop the tank to inspect the controller. I assume the schrader valve on the HPFP would be pressurized to the theoretical 5-6 bar low pressure value?

[vvenom800tt]

I chased a p0089 for ever as well.

I replaced everything under the sun and lastly it was THE HPFP for me that fixed it.

Guess i got lucky.

I replaced everything.

LPFP
PRV
G410
Fuel Filter
Air Filter
Spark Plugs
Cam Follower
Fuel pump controller.

It was finally the HPFP that fixed it.

Make sure that you got at least VDO OR OEM LPFP (Green top). As i got a cheap one that was bad (white top)

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[raerwin72]

The LPFP I got was the VDO assembled by ECS tuning one (green top) and didn't change anything. OEM HPFP didn't solve my issue unfortunately. Would you happen to have any data from VCDS from before and after the HPFP? I'd be curious as to know what low pressure readings you were seeing.

[vvenom800tt]

The LPFP I got was the VDO assembled by ECS tuning one (green top) and didn't change anything. OEM HPFP didn't solve my issue unfortunately. Would you happen to have any data from VCDS from before and after the HPFP? I'd be curious as to know what low pressure readings you were seeing.

I didnt get any logs done.

I just know my duty cycle was over 60% when my new LPFP (the bad one i got) shit the bed.

Could it be a PRV issue?

N75?

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[raerwin72]

Could it be a PRV issue?

well when I log the fuel rail pressure after a heat soak I can see that the pressure increases from 50 bar up to at least 100. From what I hear it would decrease if the PVR was bad, and I still would expect the G410 reading to at least bounce around at idle instead of a super constant value. I'm really curious to know if people are seeing 5V at the G410 vcc while plugged in and running. To me it seems like either both the new and old sensors are internally shorted, or the voltage supply circuit is falling out of saturation on the ECU. But I have no way of knowing what the proper behavior of this circuit is.

N75?

Google seems to show that as a waste gate solenoid? I'd be flabbergasted if that had an impact on the fuel reading. But it seems like almost anything can set this damn P code off so I don't know.

[raerwin72]

Also I would like to re-iterate that I am having zero stalling, starting issues, or abnormal engine idle problems. Just looks to me like the ecu is telling the pump controller to increase output due to it thinking I have low pressure. In all honestly I think I'm lucky that the car isn't failing with a pressure reading above 6 bar telling the pump to chill out and starve me of fuel. I just don't want to drive it at 80+ duty cycle all the time and burn out a new pump prematurely.

[EvolutionArmory]

Have to tried replacing the fuel pump relay and the ECU relay under the ECU? Those 2 relays supply power to a lot of different ECU sub components in the engine bay.

As a Hail Mary you could go to Audi to see if you have the most current update to your ECU software. Maybe there is a software revision to address it for your ECU box code.

You can diagnose your fuel pressure sensor by hooking up a mechanical gauge to your fuel system and checking block 103 with VCDS. The gauge should read approximately 1 bar less than VCDS. If the VCDS reading is way off after you take that 1 bar into consideration, your sensor is probably faulty.

Or you can disconnect your HPFP plug and look at MVB 103 field one and compare it to 106 field one. If the values are half a bar off from each other, it could be a bad G410 sensor.

This TSB is for a VW BPY motor but the same principals apply. https://www.goapr.com/images/support...7-69%20TSB.pdf



Also make sure you have a 6.5 bar fuel filter and not a 4.5 bar fuel filter installed.

[raerwin72]

Have to tried replacing the fuel pump relay and the ECU relay under the ECU? Those 2 relays supply power to a lot of different ECU sub components in the engine bay.

I will be taking the ECU out hopefully today or tomorrow to check. I have not been able to get the plastic ECU box cover off yet to see what else is in there, but are you talking about fuses and relays near the main ECU coupler?

As a Hail Mary you could go to Audi to see if you have the most current update to your ECU software. Maybe there is a software revision to address it for your ECU box code.

Now that Audi got my address from my registration, apparently my airbag recall was never done. Hopefully the dealer can check the SW for me while he's there.

You can diagnose your fuel pressure sensor by hooking up a mechanical gauge to your fuel system and checking block 103 with VCDS. The gauge should read approximately 1 bar less than VCDS. If the VCDS reading is way off after you take that 1 bar into consideration, your sensor is probably faulty.

Or you can disconnect your HPFP plug and look at MVB 103 field one and compare it to 106 field one. If the values are half a bar off from each other, it could be a bad G410 sensor.

This TSB is for a VW BPY motor but the same principals apply. https://www.goapr.com/images/support...7-69%20TSB.pdf

I was aware of this, but even if I did see the correct pressure on the mechanical gauge this test would likely point back to my current theory of a faulty brand new sensor or ECU issue. If the gauge was reading the same as the sensor (after 1 bar adjustment) then I would be shocked at how steady the low pressure values are (doesn't fluctuate by more than +/- 0.01 bar), even during acceleration.

Also make sure you have a 6.5 bar fuel filter and not a 4.5 bar fuel filter installed.

New OEM filter with the big ol' "6.0 bar" printed right on it (4F0 201 511 E).

[EvolutionArmory]

Under the ECU. 2 614 relays.

You gotta take the wiper arm off in order to get to the rear housing bolts on the ECU cover.

[vvenom800tt]

well when I log the fuel rail pressure after a heat soak I can see that the pressure increases from 50 bar up to at least 100. From what I hear it would decrease if the PVR was bad, and I still would expect the G410 reading to at least bounce around at idle instead of a super constant value. I'm really curious to know if people are seeing 5V at the G410 vcc while plugged in and running. To me it seems like either both the new and old sensors are internally shorted, or the voltage supply circuit is falling out of saturation on the ECU. But I have no way of knowing what the proper behavior of this circuit is.



Google seems to show that as a waste gate solenoid? I'd be flabbergasted if that had an impact on the fuel reading. But it seems like almost anything can set this damn P code off so I don't know.

I had some weird symptoms before that felt like fuel cuts.

Ended up being a bad N75

Thats why i threw it out there.

But if the car drives fine then its definitely not that

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[raerwin72]

Thanks for the input guys. I got some updates for you, but no solution yet. I took the ECU out today to check for corrosion or blown fuses and everything was clean under that box. I took a look at those 614 relays you mentioned EvolutionArmory, and I noticed some discoloration on the two main leads of the relays themselves. I assumed it was from heat or high current since it looked like when chrome exhaust turns blueish brown. I carefully took the caps off the relays to see if anything was burnt inside but all the components looked like they were new.

I then wanted to probe the ECU connector and check continuity to the G410 connector. I gotta say those safety screws holding the ECU connector on were a pain, but not as bad as I was originally expecting. Using a T-pin that was too fat for the ECU coupler, I was only able to track down the VCC pin location, which looked a different color purple than what I was probing on the sensor connector (missing black stripe at ECU I think). From my experience I think it isn't uncommon for two or more sensors to share a common VCC pin at the ECU so maybe it T's off somewhere down the harness?

I don't have a circuit diagram for this car, wish I had a Bentley manual or .pdf (wink wink), so that I could figure out if there are other sensors tied to this VCC that may be contributing to this voltage drop. I thought too that maybe my multimeter input resistance was throwing off my voltage readings. Usually happens with cheap ones, but my pride and joy of a tool Fluke DMM apparently has a 10M ohm input so I highly doubt that was the case. Unless that is Bosch put some circuit conditioning on that Vcc with an even larger resistance....

Anyways, I decided to once and for all measure the fuel pressure at the HPFP to help me rule out clogged lines. I'm not sure if this was the correct procedure so please let me know if I should do a re-test (I'd rather not though). With my cheap fuel injection test kit I found the corresponding fitting to screw onto the schrader valve off of the HPFP and ran the engine. I then used the purge valve on the tester to remove as much air as I could, but the kit is crappy so I think it was sucking air in at the bleed button whenever I would hit it. Regardless though I was seeing the needle bounce between 5 and 5.5 bar at a rate that I imagine corresponded to the three lobes on the intake cam. So if the gauge is reading 5-5.5 bar then that would mean that the G410 sensor should theoretically show me 6-6.5 bar correct? I didn't have my buddy's VAGCOM at the time to check function blocks, but the CEL came on at some point during me testing the pressure so I doubt I would see anything different than before.

When I get a chance I will find an actual probe small enough to fit in the ECU coupler and probe for continuity more thoroughly to see if there are any funky wiring issues, but I suspect not based on the car's condition. If anyone has a manual that shows the ECU wiring diagram, I would love to see what else if anything is connected to the Vcc line that G410 is on. My plan would be to unplug all those sensors and see if anything changes on the VCDS for group 103.

Since I tested actual pressure at the brand new HPFP, my only options left are buying yet another G410, something funky with wiring, another sensor affecting the G410, or the damn ECU got fried on that circuit. If anyone has further suggestions that I may be missing please tell me, I'm all ears at this point.

[raerwin72]

So I finally fixed my issue, and with a couple piecemeal wiring diagrams I found out that what I though was Vcc was actually the pull-up to 5V on the ECU signal input.

Unfortunately the service manuals I found for an FSI stated that the G410 connector should have pin 1 reading ground, pin two ~0V for signal, and pin 3 5V for Vcc. Since I had already measured 5V on pin 2 I had assumed that somehow my wiring got crossed and signal was where power was supposed to be or something. Because of this I tried swapping the two wires in the connector and reading block 103 in VCDS to see if the fuel pressure was fixed, but unfortunately nothing changed.

I also found out that the intake runner flap unit shares a common power and ground with the G410 sensor. I figured with out there being any flap codes I would check to see if I was getting the proper voltage at that connector. Sure enough I found 5v at the Vcc pin, but noticed that the wire color matched the wire color on my G410 connector that had 0V, and no continuity to ground.

Fast forward to about a week ago, I was able to get a hold of someone who has another running FSI engine and I was able to measure correct voltages at the G410. This was where I found out that the low pressure fuel sensor has an internal pull-up in the ECU. For anyone else having a similar issue, note that pins 2 and 3 should BOTH have ~5V with reference to ground.

Since I knew that my Vcc had 0V and no continuity to ground I figured I MUST have an open circuit between the intake runner flap and the G410. I started disconnecting sensors and pulling back the harness from back behind the timing chain cover and noticed a small rip in the thermal wiring loom. I then noticed that the cut went deep into electrical tape under the wire loom. Sure enough there was a little end of the white and black wire sticking out not connected to anything.

Ultimately I soldered the two ends of the wire back together and heat-shrinked (heat-shrunk?) the wire and re wrapped the harness. Eagerly I read the 103 group values in VCDS and thankfully the fuel pressure values were right where they were supposed to be. Took the car for a few test drives to see if the code would come back, and so far the dash has been CEL free for a couple days now!

I've had this car and CEL for over a year now and I believe I FINALLY got the cursed P0089 to go away. Unfortunately I wasn't able to figure out I had a wiring issue until after replacing both low and high pressure pumps, filter, and sensor.... but I was on the verge of buying a new ECU thinking the input A/D converter was fried, and thankfully I didn't.

I just want to say I appreciate all the help from the forum, and I really wish Audi had better fault detection for open circuit condition. This should not have been a "pressure outside specified value" fault but more of an open/short fault code. I guess now I can start thinking about some go fast goodies, and knowing that a CEL will now mean something other than "Oh that? Yeah it's nothing" :D

[Okedokey]

so a broken wire(s)?

[klrider44]

So I finally fixed my issue, and with a couple piecemeal wiring diagrams I found out that what I though was Vcc was actually the pull-up to 5V on the ECU signal input.

Unfortunately the service manuals I found for an FSI stated that the G410 connector should have pin 1 reading ground, pin two ~0V for signal, and pin 3 5V for Vcc. Since I had already measured 5V on pin 2 I had assumed that somehow my wiring got crossed and signal was where power was supposed to be or something. Because of this I tried swapping the two wires in the connector and reading block 103 in VCDS to see if the fuel pressure was fixed, but unfortunately nothing changed.

I also found out that the intake runner flap unit shares a common power and ground with the G410 sensor. I figured with out there being any flap codes I would check to see if I was getting the proper voltage at that connector. Sure enough I found 5v at the Vcc pin, but noticed that the wire color matched the wire color on my G410 connector that had 0V, and no continuity to ground.

Fast forward to about a week ago, I was able to get a hold of someone who has another running FSI engine and I was able to measure correct voltages at the G410. This was where I found out that the low pressure fuel sensor has an internal pull-up in the ECU. For anyone else having a similar issue, note that pins 2 and 3 should BOTH have ~5V with reference to ground.

Since I knew that my Vcc had 0V and no continuity to ground I figured I MUST have an open circuit between the intake runner flap and the G410. I started disconnecting sensors and pulling back the harness from back behind the timing chain cover and noticed a small rip in the thermal wiring loom. I then noticed that the cut went deep into electrical tape under the wire loom. Sure enough there was a little end of the white and black wire sticking out not connected to anything.

Ultimately I soldered the two ends of the wire back together and heat-shrinked (heat-shrunk?) the wire and re wrapped the harness. Eagerly I read the 103 group values in VCDS and thankfully the fuel pressure values were right where they were supposed to be. Took the car for a few test drives to see if the code would come back, and so far the dash has been CEL free for a couple days now!

I've had this car and CEL for over a year now and I believe I FINALLY got the cursed P0089 to go away. Unfortunately I wasn't able to figure out I had a wiring issue until after replacing both low and high pressure pumps, filter, and sensor.... but I was on the verge of buying a new ECU thinking the input A/D converter was fried, and thankfully I didn't.

I just want to say I appreciate all the help from the forum, and I really wish Audi had better fault detection for open circuit condition. This should not have been a "pressure outside specified value" fault but more of an open/short fault code. I guess now I can start thinking about some go fast goodies, and knowing that a CEL will now mean something other than "Oh that? Yeah it's nothing" :D

This could be huge, so many people have that dreaded code and this may be accounting for a lot them. Snap some pictures of exactly where the wire was broken at. It seems there are quite a few common wires that get broken on this platform. For instance: one of the headlight flapper wires, fuel level sensor wire, and now possibly this wire you are referring to.


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[raerwin72]

so a broken wire(s)?

Yeah, sorry if my post was a little all over the place... I was typing it up while having a beverage and watching some Netflix on the couch There was one broken wire (white with black stripe) that was supposed to supply power to pin 3 of the G410 sensor.

I had unreasonably ruled out a broken wire about a year ago when I saw that I was getting a solid ground reading on pin 1, a solid 4.95V on pin 2 (when connector is unplugged), and a floating voltage on pin 3. I assumed 1 and 2 were power and ground, and 3 was the signal wire because of these values but only now realized that pins 2 AND 3 are supposed to have ~5V at the connector.

This could be huge, so many people have that dreaded code and this may be accounting for a lot them. Snap some pictures of exactly where the wire was broken at. It seems there are quite a few common wires that get broken on this platform. For instance: one of the headlight flapper wires, fuel level sensor wire, and now possibly this wire you are referring to.


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I'm fairly new to these forum platforms so I really don't know how to post pics, but if anyone would like to teach me I will for sure get some quality ones to post.

I definitely hope that at least one other poor soul can save some time or money from all the pain and suffering I went through. Not to mention all the costly parts that I replaced on a whim because I could not get access to wiring diagram information or service manuals. I will mention again that the service manual for testing the G410 sensor that I did end up finding was completely misleading. It might not have been exactly for a B7 A4 but definitely an Audi 2.0t of similar era, and the method for ruling out bad wiring was if pin 1 had continuity to battery ground, pin 2 had ~0V with reference to battery ground, and Pin 3 had ~5V with reference to ground. Pin 2 info is completely incorrect for the ECU and sensor that is in our cars, and if anyone else has out of date or incorrect information like this, then they would most likely be chasing their tail like I was on other possible causes.

I've read the threads where people said the dealer replaced the sensor 2-3 times, and went through 2 Hpumps, an intake pump, 2 fuel filters, lift pump control module, and still have the Pcode. I find it appalling that there aren't any better troubleshooting information for this clearly popular FSI issue. But what makes me more upset is how the fault detection for these cars seems to default anything fuel related to just one code... guess that's why a lot of cars after this just simply removed the sensor and fault detection form the car.

My advice for anyone troubleshooting this issue that also has access to a VAGCom or whatever is follows:

1.) Replace the fuel filter first (6.0 bar or the 6.6 can't remember) then take some measurements (group 103 and 106).

2.) If group 103 measures less than 4 Bar, measure the ACTUAL fuel pressure of the system with a mechanical gauge before you replace anything else. There is a schrader valve on the back of the Hpump that will work with most fuel injection pressure testers. I just followed the process in the P0089 Audi TSB. My physical pressure was spot on with the +/- 1Bar gauge pressure difference. This was how I knew my ECU wasn't getting a good reading from the sensor... I just didn't know why it was still wrong with a new sensor. If the values are completely different then I would check voltages at the connector and make sure you have 0V on Pin 1, and 5V on pins 2 and 3 with respect to ground... if so replace the sensor.

3.) If the sensor and mechanical pressure measurements match up, then I would look towards the back of the car for the issue. In tank fuel pump, pump control module, or debris in fuel lines.

4.) If the mechanical pressure is fine but the electrical pressure is wrong, then turn to the group 106 measurements. Mine were roughly 50 bar at idle, maybe 70-90 when I blipped the throttle. If the 106 measurements seem correct then I would suspect the Hpump is OK. If the fuel rail pressure is low then I would suspect the cam follower or Hpump is on it's way out. If not the cam follower then more specifically the solenoid on the Hpump that you cant buy separate is probably bad, or an issue with that connector's wiring (though I believe the P0087 or P0088 could would come on in addition, or instead of, the P0089).

*I don't recommend this, but I know of a friend who was able to replace just the Hpump solenoid with my old one for his S6 because his connector was broken and didn't want to pay for a whole new pump. Part numbers were slightly different but he didn't care and it worked. I'm sure the Hpumps are probably calibrated with that specific solenoid or whatever and that might be why they don't sell separate, but it technically can be replaced if you have to find one used.

5.) CHECK THE INTAKE FLAPS! I had no idea that the 5 pin connector on the flapper motor share the same power and ground wires that the G410 connector does. Pin 1 on the flapper connector should read 5V and have continuity with pin 3 on the G410 connector, while pin 3 on the flap connector should read 0V and have continuity with pin 1 on the G410 connector. If these look good, and you get 5V on pin 2 of the G410, then your wiring is most likely alright. If anything doesn't match up here then you need to check for open or shorts.

6.) If everything else fails then double check your fuses, ground connections, and the relays under the ECU even if you checked them before. I know I've overlooked faulty fuses and grounds before and hated myself for wasting too much time on something stupid. The ECU has some pretty good internal circuit protection that I can personally attest to so don't go replacing the ECU unless it's literally the LAST thing you replace. I've actually swapped the ground, signal, and power lines to the sensor, grounded and shorted them, and even imparted a separate 5V source to the wrong lines (less than 500mA current though) and the ECU ended up being fine.


I'm just glad that everything I replaced probably needed to be anyways and I didn't end up replacing the ECU and go through the hassle of the dealer immobilizer/VIN registration. Fuel filter and lift pump probably were bad anyways after the previous owners ignoring this code and running the pump at 85-95% duty cycle for a long time due to the wrong sensor reading. The Hpump needed to be replaced because the cam follower must have punched through at some point and caused nasty wear on the pump plunger. Unfortunately now I kinda want to rebuild it with APR upgrade in the event I go stage 2+ but I would hate to mess up this brand new OEM one I dished out loads of money for.

[Okedokey]

So (not being a dick) but the root-cause was

"I assumed 1 and 2 were power and ground, and 3 was the signal wire because of these values but only now realized that pins 2 AND 3 are supposed to have ~5V at the connector."

The first thing always - resistance measures to check continuity and then voltages.

glad you fixed it.

[raerwin72]

So (not being a dick) but the root-cause was


The first thing always - resistance measures to check continuity and then voltages.

glad you fixed it.

You are correct. But without any wiring diagrams to reliably go off of (and I've asked around for some) I was going at checking electrical characteristics blind. All the schematics I found had wire colors and pin numbers that did not match. They obviously weren't for a B7 A4 but hey worth a shot. not only that but no where could I find that there was a pull-up to 5V on the signal wire so I would have made the other assumption that my wires got crossed if I did have the correct diagram. Also nearly impossible to check continuity to ECU coupler with multimeter probes. I used a sewing needle to prob in there but had mixed results getting good contact. I should definitely have figured out it was an open circuit sooner, but the harness looked damn near perfect upon visual inspection. I had to really pull the whole thing out before I found the issue.

[Okedokey]

True. You're did it hard, but worked it out.. respect.

For anyone in the future, here is a diagram that may help.

CFD.jpg

[t_wicx]

Any chance I could get a picture of where this is on the motor, I have the same code as well and it's making me want to sell the car. I'm losing my mind over this code! I have no power loss. It's given me a couple of misfires Once! And they were soft misfire codes. After clearing just the p0089 came up. I can't get this thing to go away and I'm not exactly super techy. I do not have vagcom as well so I'm kinda screwed someone please help :( I've read the insanely long p0089 thread and will be replacing my g410 but I'm terrified that's not going to fix it as the car runs completely fine.

[mc_hotmail]

Short version is the 5V Vcc wire was cut in the engine harness between the firewall and timing chain cover.

I didn't notice this thread before, but I know what he referred to. In case you don't know what and where the high pressure fuel pump (HPFP) is in a B7, watch this video between timestamp 2:10 and 2:12 where the guy removed 2 plugs off the HPFP. Trace those wire will lead you to the back of the cam cover then into a big wire harness with a leather wrapper thru the firewall.

[raerwin72]

Any chance I could get a picture of where this is on the motor

If you are referring to the HPUMP itself then yeah mc_hotmail's post can help.

For the cut wire that I had, it was really hard to get good pictures since the wire harness is tucked between the head and the firewall pretty good. There wasn't much slack in the harness to pull it up and out to get a good picture but I'll post what I got.

This one is just the general location of where my open circuit was. You can see the HPUMP on the bottom right, and vacuum pump on the top right. Essentially the cut in the wire was behind and under the vacuum pump in the big wire harness with the black heat resistant wrapping.



This image is the actual wire that was cut. I had to pull the wire harness looming back quite a bit to get to the end of the white wire (5V reference to the G410). Again you can see the HPUMP in the photo, with the black plastic cap on the schrader valve used for pressure testing the fuel system. Was a tight squeeze to re-solder everything.



I guess if you are having the same symptoms as me (no power loss or drive ability issues) replacing the G410 would be the easiest and cheapest option. Also check the part number to see if you still have an old revision of the sensor. Since they are known to fail it's not out of realm of possibility.

Lastly for anyone electrically testing the harness, I just want to reiterate that there should be two pins that read ~5V when unplugged from the G410, and the 3rd one with continuity to ground. Until I found a second car to test on, it was never clear to me that the signal wire should be internally pulled up to 5 within the ECU. Makes sense in hindsight, but there was just no way for me to know for sure how the unit worked.

[EvolutionArmory]

A multimeter is your best friend when you own an Audi.

Any time you have a fault with something that runs on electricity you should be asking yourself does the part get power, where is the ground and what is the internal resistance of the part suppose to be.

A 20 dollar multimeter and a wire diagram can save you hundreds of dollars and countless hours.

[raerwin72]

Any time you have a fault with something that runs on electricity you should be asking yourself does the part get power, where is the ground and what is the internal resistance of the part suppose to be.

This is exactly what I was doing for a whole year. I saw 5V, had continuity to ground, and had resistance measurements for both the old and new G410 sensors, so everything electrical seemed fine I thought. I am by no means a noob electrical troubleshooter if that is what you are getting at, but for others who might not be familiar with electronics, I agree these should be the first steps for diagnosis.

A 20 dollar multimeter and a wire diagram can save you hundreds of dollars and countless hours.

I agree. This is why I asked if anyone had a wiring diagram back in post #11 before i spent nearly a year until I found another FSI to test on. And before anyone says "oh just get a Bentley, you'd be a fool to own an Audi without one"... I know. I love the Bentley manuals. The one I have for my 81 Rabbit is a godsend when I was working on the CIS fuel system. Unfortunately when looking for a B7 A4 manual, I found several other users on here stating that like the 2000 and newer Bentley manual quality is pretty inferior to what they used to be. I didn't want to waste money on one and risk not getting the diagram I needed.

Additionally, like I stated before the G410 TSB troubleshooting procedure was incorrect in that when measuring for voltage at the connector, they state that the signal should be "near zero Volts" which is incorrect and led me to believe I had a different issue all together.

[EvolutionArmory]

I’m not making any assumptions about what you know or don’t know or your “noob” status or lack of it


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[ABG-A4b7]

Thank you ALL involved! Okedokey, what is the source for the diagram you provided? I would like to purchase similar proper documentation if you folks have found it useful in practice.