P0240 & P0045(F3) codes once a month

[1nS4ne]

Hello,

I just recently purchased a used 2016 Audi S6 and about a week after getting it home I got a CEL. So I plugged in my OBDII scanner and it came up with two codes, P0240: turbocharger boost pressure sensor B - range/performance problem & P0045(F3): turbocharger boost control solenoid open circuit. I cleared them thinking it could be a one-off event, but they just came back about a month later. I googled them and it doesn't appear any other forum members have gotten these codes so that makes it tough to self-troubleshoot. I was wondering what the forums' professional opinion on this is? Just a bad sensor that needs replacing or something more sinister underlying this?

20210828_234532877_iOS.jpg

Thanks!

[gk1]

P0240 Turbocharger/Supercharger Boost Sensor "B" Circuit Range / Performance
• diff. pressure in front of throttle to average value of all pressure sensors @ start < -6.00[kPa] or > 6.00[kPa]
with engine shut-offtime> 5.0 [s] & engine speed <300 [rpm]
or
• diff. boost pressure signal vs. barometric sensor signal >23.00 [kPa] or <-23.00 [kPa]
with engine speed <1000 [rpm] & throttle position <5.00 [%]

Check the Charge air pressure sensor 2 - G447- .
Check the charge air system and intake system for leaks. (I'd check wastegates and Bypass valves too.)

The Charge air pressure sensor 2 - G447- is located in the inlet to the intake manifold. The Engine Control Module - J623- uses the sensor’s signal to regulate the charge air pressure. There is no substitute function in the event of signal failure. Charge air
pressure regulation is shut off, leading to a significant reduction in engine output.

• Fuses OK.
• Battery voltage OK
• Switch OFF all and electronic accessories.
• Vehicles with Auto. Transmission, ensure Selector Lever position is in “P”.
• Vehicles with Manual Transmission, ensure Gear Shift Lever position is in “N” with Parking Brake applied.
• Coolant Temperature: ≥ 80 °C.

• DISCONNECT: Charge air pressure sensor 2- G447- connector
• IGNITION: ON
• CHECK: Charge air pressure sensor 2 - G447-wiring connector terminals 1 to 3 for voltage
• SPECIFIED VALUE: About 5.0 V
• IGNITION: OFF

(All other tests require ECM removal.)
If I didn't find any obvious wiring issues I'd probably just replace it.
038906051K
https://www.ecstuning.com/b-genuine-...ns/038906051k/

Also check N75 valve and wiring that is the only thing I can think of that may be reflected in the generic P0045 code even though it is really called "Wastegate Bypass Regulator Valve".

[1nS4ne]

EDIT: I found a diagram of where the N75 is located on the 4.0T, would you happen to know the troubleshooting steps for that as well, by chance? Same procedure as checking the G447 sensor? 5.0V for each pin while ignition ON? Or completely different procedure?

Wow, very informative, I can't thank you enough! I will definitely take a look at the G447 sensor and and wiring and replace if needed. I am a little confused on the location of the N75 valve on the 4.0T engine though, I was not able to find a diagram of the location of that valve, would you happen to know where to look for that?

[qcrazy]

#6...
Screenshot_20210918-091517_Drive.jpg

[qcrazy]

No specific testing procedure listed. But from the P codes, it appears it runs battery voltage to ground...
Screenshot_20210918-093642_Drive.jpg

[1nS4ne]

Thank you! Looks like its a little deeper on the engine than the first diagram I was looking at made it seem. So when you say battery to ground is it likely I will be seeing something around 12.0V when testing using a voltmeter?

[qcrazy]

Yes B+ means 12-14V. But to test it the car would have to be calling for it. So that may not help on testing the voltage side. Obviously you can test the ground whenever.

Here is more background on the boost control...
Screenshot_20210918-115448_Drive.jpg

You can see that the N75 controls boost for both turbos. Since you are only having trouble with one, that may point away from the N75.

If I was in your shoes I would do the following....
--Trace the vaccum lines from the wastegates to the N75 valve. Make sure they are hooked up (look closely) and there are no tears. Sometimes they look hooked up to the wastegates, but they are not.
--Pay particular attention to the US drivers side (Bank 2).
--If those are okay, look down by the N75 and make sure it is plugged in...if you can see. You may not be able to see anything.

I hate to be the one to tell you this but sometimes this means you have a bad turbo. If you find nothing above, check your turbos.

Hopefully it is just a vacuum line that was left disconnected, or a bad sensor.

[gk1]

Wastegate Bypass Regulator Valve - N75- , Checking Function
Both the boost and intake pressures are used to control the wastegate of the turbocharger. These pressure signals are supplied to the Engine Control Module - J623- , which then sends a pulse-width modulated signal to the Wastegate Bypass Regulator Valve - N75- . As a result Wastegate Bypass Regulator Valve -A6, S6, S7, A8, S8 2013 ➤
N75- controls vacuum supply to the Pressure Unit, which directly acts on the wastegate via a connecting rod. This control system regulates the turbine speed and sets the maximum boost pressure.

• Fuses OK.
• Battery voltage OK
• Switch OFF All and electronic accessories
• Vehicles with Auto. Transmission, ensure Selector Lever position is in “P”.
• Vehicles with Manual Transmission, ensure Shifter Lever position is in “N” with Parking Brake applied.
• Coolant Temperature: ≥ 20° C.

• IGNITION: OFF
• DISCONNECT: Wastegate Bypass Regulator Valve - N75- connector
• CHECK: Wastegate Bypass Regulator Valve -N75- component connector terminals 1 to 2 for resistance.
• SPECIFIED VALUE: 13 – 17 Ω (± 4 Ω @ approx. 20° C)

• IGNITION: ON
• CHECK: Wastegate Bypass Regulator Valve -N75- connector terminal 1 to ground.
• SPECIFIED VALUE: Battery voltage
• IGNITION: OFF

Otherwise, again, removing ECM to test further.
I believe this is the part, but be sure to check first.
https://www.ecstuning.com/b-genuine-...6h906283b~oem/

[1nS4ne]

Thank you guys so much for the information, you guys are making this forum an amazing resource for owners. When I purchased the car one of my asks was for the entire Audi service history and sure enough when I looked back at it the last performed maintenance before I took ownership was the replacement of the G447 sensor and that was barely 1000 miles ago.

Here me out, this leads me to believe that the G447 charge air pressure sensor is not the issue and that the N75 bypass valve is. The P0240 code stated that there was an issue with range/performance and did not report an actual issue with itself (voltage irregularities, etc.) so the P0240 was just being triggered by an irregular value caused by an already occurring issue/failure which I assume is the N75 bypass valve's fault. Now the P0045(F3) code did say OPEN CIRCUIT which I assume relates to itself or its wiring being faulty.

An open circuit is defined as an electrical circuit in which the continuity is broken so that current does not flow, so is this P0045(F3) the diagnostics telling me it's losing electrical connection to the N75 bypass valve? Like I said in the title these codes happen maybe once a month and its always at startup. Could this mean that my N75 bypass valve might be on its way out?

What is your opinion on this? Is my deduction sound? Or am I inferring the meaning of the open circuit warning wrong? Thanks again!

g447.PNG

[gk1]

Open circuit means either wiring or possibly sensor/component fault.
The steps I did not list which require ECM removal are to help determine if it is a wiring issue, but removing the ECM is involved and you could potentially do more damage than good unless you specifically suspect there is wiring damage I would not do them.
If you think they did not damage any wiring when replacing the G447 previously, then perhaps it is the N75 that is the issue then.
However it is also possible to have a bad brand new part albeit rare.

If you can test and you don't get the results listed....

• IGNITION: OFF
• DISCONNECT: Wastegate Bypass Regulator Valve - N75- connector
• CHECK: Wastegate Bypass Regulator Valve -N75- component connector terminals 1 to 2 for resistance.
• SPECIFIED VALUE: 13 – 17 Ω (± 4 Ω @ approx. 20° C)

...then the action = replace N75.

If you do the other test and don't get battery voltage to the N75 connector then it is check wiring and fuses.

[1nS4ne]

Yes, I do not plan on messing about with the ECM if it comes to that. I will visually inspect the harnesses for both the G447 and N75 and trace as much wiring as possible to make sure there are no lacerations in them.

The biggest dilemma I face with home troubleshooting this is the location of the N75, I checked the shop manual and it calls for removing the radiator first do you or anyone know if its possible to remove it without that hassle?

[qcrazy]

Removing the radiator would be considered a hassle by most people.

I understand your logic, but you have to consider that P0045 is a generic OBD code, not an Audi specific code. It is not referring to a specific part (e.g. the N75) being "OPEN". It is referring to the entire boost control system being open...or in other words it has found an abnormal reading in the boost control "circuit" (e.g. system).

The ECU outputs a signal to N75 to develop a targeted boost. G447 is a sensor that send an input to the ECU in response. The ECU has a map of values that at "X" N75 output, G447 should represent "Y" input. What P0045 is saying is that the output being sent to N75, does not match the value it should be seeing at G447. And whatever value is sent to N75, is not reflected appropriately at G447. Or in other words, there is an open "circuit" between the output and the input.

One important point to note here, is you need to take both of these codes together. P0045 says the boost control system is not working correctly. P0240 is saying your are getting an out of range reading on Bank 2. Since the second code is only on Bank 2, that means the car IS seeing the correct readings on Bank 1. With that, we know that at least some portions of the system are working.

With that said, you have to figure out what is "open" in the boost control circuit.
--It could be G447, but that seems unlikely since it was just replaced.
--It could be N75 (or the wiring), but that seems unlikely since you are not seeing a similar issue on Bank 1.
--It could be a bad Bank 2 wastegate
--It could be a bad vacuum line between the wastegate and the N75
--It could be a bad turbo
--It could be boost leak before or around G447

You could check the N75 if you want, but that is a lot of work. And I think it is not as likely to be the culprit because you are not having a similar issue on Bank 1.

On that list above, the easiest things to check is the vacuum line and wastegate. The second easiest thing to check is the turbo.

Since the previous owner appears to have been fighting this issue as well, my bet is the turbo. They may have figured it out and dumped the car. I wonder if your turbine broke off and the turbo is not even spinning anymore?

[1nS4ne]

Ah, so I took the "open circuit" part too literally. The open circuit it was referring to was the entire boost control circuit.

I appreciate you walking me through your deductive reasoning. What you are saying does make good sense about it only being bad on bank 2 so its unlikely that the N75 is completely the culprit. I will start with checking the vacuum lines then the wastegates. How should I go about checking the wastegate though? Do I just push/pull the linkage arm to see if it has smooth operation? What exactly do you look for when checking the wastegate for failure?

Also, should I not find any issues with the aforementioned parts and start to check the turbo all I need to do is remove the silicone pipe on bank 2 and see if there is any play in the stem of the impeller, correct? Check the fins and sidewalls for contact? Any other visual queues?

[qcrazy]

Trace the vacuum lines, make sure they are all connected from the wastegate to the N75 (best you can see). Look closely at the wastegate connection, some people report they fall off there.

To test the wastegate, I would disconnect the vacuum line and use a mitivac to make sure you can pull a vacuum on the wastegate. This makes sure the diaphragm in the wastegate hasn't split. It can be hard to get the vacuum line off the wastegate, so it may be easier to connect the mitivac in the middle of the vacuum line run.

To check the turbos you actually want to pull off the inlet pipe coming from the airbox. Not exactly easy to do, but easier than getting at the N75. The easiest way to inspect is to disconnect the airbox couplings and use a borescope to look at the compressor wheels. If you don't have access to a borescope, then you just need to unbolt the inlets (two bolts on each inlet at the turbo), which is a bit more work but still manageable.

I hope my guess is wrong and you find something really simple to fix this. Good luck.

[1nS4ne]

OK great, this weekend I'll pop the hood and trace those vacuum lines and check the wastegate connection. I ordered a fairly cheap vacuum gun similar to the VAS 6213 tool Audi uses to troubleshoot vacuum issues and I'll use it to test the bank 2 wastegate if I don't find an obvious issue with the lines.

Let me ask you this for future reference, if I were to use a Ross-Tech VCDS to read these codes, would I get a more Audi-specific narrowed-down code or would it be the same reading as the generic OBDII reader I am using now?

[qcrazy]

Good question. I had some time tonight so I looked into this further. I didn't like that we couldn't find P0045 listed. So I did some digging...

In the S6 manual I did find the code...
Screenshot_20210922-225057_Drive.jpg

If you look at the codes listed in the post above it is a different code and it doesn't list the N75 specifically, like above. A little more digging and I found some general reference information on the code. This was in a different manual...and for a TDI...
Screenshot_20210922-220253_Drive.jpg

Definitely aligns that it is in fact a wiring issue.

So then, what is the "Boost Control Solenoid". It does not seem to be the wastegate control solenoid (N75). So a bit more searching and I see that years ago the N249 used to be called the "Boost Control Valve". We typically just call these the recirculation valves or the diverter valves now.

On the 4.0T we have two diverter valves...not one. We have the N249 (Bank 1) and the N427 (Bank 2).
Screenshot_20210922-225509_Drive.jpg

If I search the DTC's I can find specific codes for the N249, but nothing listed specific for the N427. I wonder if your N427 is the issue here? It would definitely explain why you are only having issues on one bank? Seem plausible?

I can't find the specific testing requirements, maybe gk1 can post them. But if nothing else...you could always compare it to Bank 1.

I kind of wonder if the dealer just forgot to plug the N427 back in? Or if they broke the retaining tab and it fell out? It is right on top and certainly easy to check. Maybe it is this simple?

Good luck!

[gk1]

Interesting point qcrazy.
But one thing. Look about ten lines up in your first list.
There are generic codes for the "Turbo Charger Bypass Valve Control" circuits. Albeit without specific N numbers
I would think you'd see those P003x00 codes if there were issues with the diverter valves or associated wiring.
Still worth checking the DV wiring too. As you mentioned they are right there on top.

From another source:
P004500
Turbocharger/Supercharger Boost Control A Circuit /Open

Variable geometry turbocharger (VGT) actuator circuit high resistance

VGT actuator circuit short circuit to ground

VGT actuator failure

ECM failure
Which is weird because we don't have VGTs.

Still...if it is not diverter valve related then signs point back to N75 since it is the only electrical component of the wastegate actuation on the 4.0T.

Also what is with the "F3" in the OP's code?
P0045(F3)
Is it a HEX subcode or something? F3 = DEC 243
Or maybe Binary meaning something else? 1111 0011

[1nS4ne]

Man I really appreciate you guys digging into this for me. I have access to the service manual for the S6 and I was able to find the removal/install page for the N427 (even though I think they typo'd and referenced the N249 because it was the topic just above this) and sure enough there are two electrical connectors running to it (or at least that's what the manual makes it seem).

n427.JPG

I have a little time later today for some minor troubleshooting so I am going to do most of the easy surface level stuff like trace the vacuum lines as much as I can and confirm electrical connections are secure, may even be able to get a few voltage readings.

And yes, that (F3) addition to the P0045 code still baffles me, it was read using a generic bluetooth OBDII reader to an android phone, do you think a more Audi-specific reader like the Ross-Tech VCDS would produce different results?

[1nS4ne]

Interesting point qcrazy.
But one thing. Look about ten lines up in your first list.
There are generic codes for the "Turbo Charger Bypass Valve Control" circuits. Albeit without specific N numbers
I would think you'd see those P003x00 codes if there were issues with the diverter valves or associated wiring.
Still worth checking the DV wiring too. As you mentioned they are right there on top.

From another source:
P004500
Turbocharger/Supercharger Boost Control A Circuit /Open
Variable geometry turbocharger (VGT) actuator circuit high resistance
VGT actuator circuit short circuit to ground
VGT actuator failure
ECM failure
Which is weird because we don't have VGTs.

Still...if it is not diverter valve related then signs point back to N75 since it is the only electrical component of the wastegate actuation on the 4.0T.

Also what is with the "F3" in the OP's code?
P0045(F3)
Is it a HEX subcode or something? F3 = DEC 243
Or maybe Binary meaning something else? 1111 0011

Holy crap, so F3 converted to decimal is 243, if you use that number in the generic trouble code format it would be P0243 and a quick Google of that resulted in:

"P0243 is a generic OBD-II code indicating that the Engine Control Module (ECM) detected the turbocharger wastegate solenoid has an open or short circuit."

What do you guys feel about that? Freaky coincidence or no?

[qcrazy]

VCDS may get more specific, if it is outside the codes available in the OBD. But it may not, if it is covered already with the OBD code. Hard to say. I would guess not here.

Interesting on the F3. Probably a coincidence...but who knows. Maybe the F3 would make a different code in VCDS?

With what we have figured out I am convinced at this point that you have wiring issue, the real question is exactly what part has the issue?

You can check the vaccum lines just make sure, it seems like they will be fine.

Then you can check the DV's since they sit right on top. Make sure they are both plugged in. Ohm out the pins on both and make sure they are comparable. I like the DV's because they would explain why only one bank is having the issue.

But...if the DV's are okay, I think that leaves the N75. If it isn't expensive you may want to have one on hand as the part itself may just have shorted out. I just don't understand why this would only affect one bank...both wastegates come off a common port on the N75.

[1nS4ne]

VCDS may get more specific, if it is outside the codes available in the OBD. But it may not, if it is covered already with the OBD code. Hard to say. I would guess not here.

Interesting on the F3. Probably a coincidence...but who knows. Maybe the F3 would make a different code in VCDS?

With what we have figured out I am convinced at this point that you have wiring issue, the real question is exactly what part has the issue?

You can check the vaccum lines just make sure, it seems like they will be fine.

Then you can check the DV's since they sit right on top. Make sure they are both plugged in. Ohm out the pins on both and make sure they are comparable. I like the DV's because they would explain why only one bank is having the issue.

But...if the DV's are okay, I think that leaves the N75. If it isn't expensive you may want to have one on hand as the part itself may just have shorted out. I just don't understand why this would only affect one bank...both wastegates come off a common port on the N75.

I traced the bank 2 wastegate vacuum line yesterday and from what wasn't covered by the coil packs cover it looked good, felt like it was firmly attached to the wastegate, the hose was all the way up in the little spy window. Once the vacuum line started turning toward the N75 I lost it, there literally is NO room between the engine and radiator, so crazy.

I checked the DV's and both are plugged in with no loose wiring. I'll have to Ohm test them this weekend.

But yes, I agree, if the N75 is the culprit I don't understand why it wouldn't affect both banks.

[qcrazy]

Real quick....I was working on my hx this evening. I noticed you can see the N75 by pulling a few pieces up front.

If you pull the radiator cover (two clips). Then there is a little rubber deflector held on by three T27 bolts you remove. Takes three minutes to get these parts out.

Then you can peak down and see the N75. Let's you look directly at the electrical connector. I couldn't get a good picture of it, but it looks to be right below the white tag tucked down there...
20210924_220010.jpg

You won't be able to do much with it. But at least see if the connector is there and the wires intact before digging in.

[1nS4ne]

Real quick....I was working on my hx this evening. I noticed you can see the N75 by pulling a few pieces up front.

If you pull the radiator cover (two clips). Then there is a little rubber deflector held on by three T27 bolts you remove. Takes three minutes to get these parts out.

Then you can peak down and see the N75. Let's you look directly at the electrical connector. I couldn't get a good picture of it, but it looks to be right below the white tag tucked down there...
20210924_220010.jpg

You won't be able to do much with it. But at least see if the connector is there and the wires intact before digging in.

Perfect, I am going to do this today and take a look and report back. Thank you!

[1nS4ne]

OK, so the OBDII reader I had was very generic and I actually have a better better one that an old neighbor had borrowed, I was able to get that back and sure enough yesterday the CEL popped back up and I was able to take another wayyyy more thorough reading, this thing went through all the modules and took at least three times as long to read than the other code reader.

This time I still got the P0240 code, BUT the second code is no longer P0045(F3), it is now 17907. Not sure what to make of that, I thought they were all supposed to have a P in front of them, but in the description it does list P1499 which I am assuming is the actual main trouble code. So the codes are now P0240 and P1499.

20211006_121843274_iOS.jpg

I looked in the service manual and P149900 is: Exhaust Gas Recirculation (EGR) Cool Switch-over Valve 2 -N381 Open circuit/short circuit to ground

I tried searching the manual for where/what module N381 but came up empty handed. With this new piece of information, I'd appreciate any insight on the source of my problem so I can (hopefully) rectify it myself without a costly trip to the dealer.

[gk1]

Sorry, I also could not find anything about N381 and google references TDI whenever that is mentioned.
I think that might be that tools best "guess" at what the fault is.

[qcrazy]

I don't think the 4.0T has an EGR. Did you check the turbo yet?

[1nS4ne]

For those who helped I thank you, I wanted to close this thread with a resolution for anyone with this issue in the future. After my 75k mile service the car was returned to me with the same DTC. I opened the hood and lo and behold a wire was completely pulled from the plug leading into the G447 sensor, just completely bare and loose. I ordered another plug with terminals included (took a whole month to get here too btw) and re-crimped all 3 wires to new terminals and inserted into the new plug and I'm happy to say the DTC has not returned.