Cam Position Sensor again...

[thesupremeg33k]

I had a problem a few months ago after replacing the head on my A4 where I was throwing P0340 & P0341 codes - turns out I had gotten the new timing belt off one tooth. Now - I am throwing just a single code:

16725 - Camshaft Position Sensor (G40): Implausible Signal
P0341 - 004 - No Signal/Communication

So far I have:
- Swapped in a new cam position sensor, no change
- Verified timing marks on crank / cam gears, both line up 100% perfectly
- Verified cam timing marks (notches) line up with arrows on bearing caps - both line up (notches to arrows)
- Tested cam position sensor wiring. The 5v & 12v lines read correctly, and the black wire shows no short to battery / ground / etc
- Tested cam position sensor with LED test light, it 'flashes' in accordance with the engine
- Checked the cam position sensor shutter wheel. The tab that locates it had gotten bent previously (DSPO), I fixed it & lined it up correctly. No change.

Its still throwing the code & acceleration off the line is very sluggish. It runs fine at highway speeds, but its an absolute dog starting off. I usually have to try to start it 2-3 times before it'll catch.

Any other ideas? I'm coming up blank on this one...

[thesupremeg33k]

Bump, any thoughts? Car has been running 100% fine since July when I did the head. When I get some free time I am going to pull the ECU & check continuity on all the wiring. If the wiring checks out fine, then what?

[MikeWire]

I know you quadruple checked it, but I bet your timing is still off a tooth.

You mentioned you replace the head...have you verified 16 links of chain from the intake->exhaust marks on the cams?

[thesupremeg33k]

Won't the timing being off a tooth throw two codes though - it did for me before?

I could bump the timing a tooth either way on the belt if you think it would be useful. Isn't there a measuring block in VCDS that shows if it is offset?

And yes - verified 16 links of chain between the intake and exhaust cam at TDC.

[CyberPMG]

Have you thought to check the plug and the wiring harness? Could be the sensor is ok, but there may be a short in the connection. Over time, the numerous heat cycles the engine goes through will dry out the rubber boots around the wire plugs exposing the wires to the heat (which will cause the shielding to become brittle and crack). I've found nearly all of the rubber boots around the electrical plugs in the engine bay to be this way and chose to get them all replaced to avoid any risk.

[walky_talky20]

I think block 093 should give you crank/cam phase offset values in degrees. 090-093 has all the cam angle stuff. But if it has a fault stored for the cam sensor signal, the info in those blocks may be weird or unavailable. Not sure.

For example, "phase position is displayed only when the phase adaptation was successfully concluded". And I'm assuming phase adaptation requires a working cam sensor signal.

[thesupremeg33k]

Agh. Welcome to my personal hell.

So - I just got around to checking out the wiring today (been a busy week). Everything is 100% fine, .5 ohms on all 3 wires from the sensor to the ECU connector. I'll post up pics I took of the timing so someone else can double-check me. With the engine at TDC the exhaust cam is spot-on, intake cam is probably a *little* under-rotated but still within the 'notch' on the cam.

...and apparently you can't read those blocks (90-93) with the free version of VCDS.

[thesupremeg33k]

I've been out of town for work lately - no chance to update this.

Pics are uploaded here: https://picasaweb.google.com/1176976...December102012 . I left them full-res for better detail. Crank mark is spot on with the mark on the TB cover. The cam mark is a hair past the one on the valve cover - but moving it a tooth would put it way before the mark. The marks on the camshafts line up pretty well - the perspective skews it.

What am I missing here?

[walky_talky20]

You do have the 4-window trigger wheel, and not the 1-window wheel, correct?

I think the next step here would be to scope (oscilloscope) the cam sensor and crank sensor together to see what is going on. You would compare these waveforms to known good signals, along with comparing their offset with respect to each other. If the signals are good, then the last option is a bad ECU. This type of testing is generally outside the scope (no pun intended) of DIY diagnostics.

[thesupremeg33k]

Yes - 4 window wheel , that's another one I thought to check.

I'm probably going to drop it off at an indie shop this week to have them check it out further. I don't have a 'scope (want one badly, however!). If the ECU does need to be replaced, can I source one from a matching car & install it myself - or does it have to be coded to the vehicle?

[Charles.waite]

Yes - 4 window wheel , that's another one I thought to check.

I'm probably going to drop it off at an indie shop this week to have them check it out further. I don't have a 'scope (want one badly, however!). If the ECU does need to be replaced, can I source one from a matching car & install it myself - or does it have to be coded to the vehicle?

Yes. Haha. You can pull one from a same model car. VCDS actually tells you the software code. When you do a scan. It'll look like this:

Address 01: Engine Labels: 06B-909-518-AMB.lbl
Part No SW: 8E0 909 518 AK HW: 8E0 909 018 A
Component: 1.8L R4/5VT G 0004

The bolded part is the software code and you want to match that up.

The rub is you either need to defeat the immobilizer or get it matched to your car at the dealer. Thats usually not cheap, so immo defeat is usually the route people take.

[mac11]

Its still throwing the code & acceleration off the line is very sluggish. It runs fine at highway speeds, but its an absolute dog starting off. I usually have to try to start it 2-3 times before it'll catch.

Any other ideas? I'm coming up blank on this one...

Ever have any resolution to this? That description sounds exactly like what my livability issues are and about every other time I drive it the car will start then die once or twice before it finally stays running but I've got p0012 code which points to the cam position sensor. But that didn't come on until I had a low oil pressure light come on so I'm not convinced its a bad sensor.

[bmx672]

Any update to this update? I have what you guys have:( 0340 and did all the usual stuff... Still have the code:(

[mac11]

What's "all the usual stuff"?

I replaced my can chain tensioner and the CEL went away in my car.

[bmx672]

I installed new cam, crank and coolant sensors... Cleaned the MAF, did a boost test, made sure all the plumbing was good
And clean. Checked cam chain and timing belt marks etc. I've done cam tensioners before... I've had them really worn out before and they haven't caused my car to not start intermittently. That's what I can't figure out. The car runs great when it starts...
But would a bad cam tensioner cause it to have a hard time starting? Man, I really don't want to spend the $ on one of that's not the cause...

[Charles.waite]

I installed new cam, crank and coolant sensors... Cleaned the MAF, did a boost test, made sure all the plumbing was good
And clean. Checked cam chain and timing belt marks etc. I've done cam tensioners before... I've had them really worn out before and they haven't caused my car to not start intermittently. That's what I can't figure out. The car runs great when it starts...
But would a bad cam tensioner cause it to have a hard time starting? Man, I really don't want to spend the $ on one of that's not the cause...

Try unplugging the Tensioner Solenoid plug when this happens and see if the issue persists. You won't cause any harm by leaving it unplugged.

[bmx672]

We'll do! And what if I unplug it and it still has a hard time starting? Just wondering where else to look later when I'm working on it in the garage!
Fuel filter/pump? Fuel pressure possibly?
Thanks!

[Dubdaze]

Triple check the wiring going to the cam sensor, by the Injectors and everything, I had the same thing. The wires get really brittle.

Car won't start right away takes 3-4 tries and acceleration is very sluggish.

[Dubdaze]

And if your timing was off you would get a crank/cam incorrect allocation fault. Not a cam sensor implausible signal fault

[bmx672]

I've triple checked the wires for the camshaft sensor... Visually they look okay. And I used the meter to check and make sure the plug had 5v (I think that's what they were supposed to have anyway from my memory). Unless they are cracked somewhere and are arcing somewhere that I can't see hence my code 0340.
I guess I'll try the fuel filter and see.
Maybe ill try that trick and have someone start it in the dark and see if anything under the hood is arcing... I've found harness wire cracks that way...

[bmx672]

I'm still getting the 0340 code:( I guess I'll check the cam sensor wire harness again:(
I didn't see it on ECS, anyone know where to get one if needed?
Thanks

[walky_talky20]

So the sensor is getting ECU ground reference as well as 5V+. It is outputting back to the ECU a 5V square wave signal that corresponds to the 4-window trigger wheel that excites the hall sensor.

So you need to check that you are getting the necessaries from the ECU all the way up to your sensor. Then check if you sensor is actually giving you a square wave output. You can check it with an ocsilloscope, but the simpler way is to use an LED-type test light while cranking the starter (remove fuel pump fuse so the engine won't start - you want it to turn over slow to watch for the flashes).

[[TSA] Oscar]

Oscilloscope ftw. If you can get a visual it'll give you a better idea of what's going on. Could be a bad ground or diode trio on the alternator causing feedback through the sensor, you would be able to see this with a waveform. Seen this on Fords. If you got a good signal than you may quite possibly have a bad ECM, but is almost never the ECM, until its the ECM... Lol

[walky_talky20]

Yeah, if the LED shows good signal, but you're still getting the code, I'd probably break out the oscilloscope as the last step before changing the ECU.

[bmx672]

I will do this test! Thanks for the feedback guys!
Two quick questions:

1) (prob a dumb question)
Would the car have trouble starting if I had bad wiring on the sensor? I would think yes. Sometimes it starts fine and sometimes it takes several tries! But even with a bad sensor couldn't it also get feedback from the crank sensor in order to start? (I put a new crank sensor in as we'll btw)

2) I have my buddies vagcom... Anything I can do with that to help anylize this situation?

[walky_talky20]

Answer 1) Absolutely. The crank sensor only knows the crank position. The crank turns 2 times (twice) per every rotation of the camshafts. So if we are talking about cylinder 1, the first rotation of the crank does the "intake" and "compression" strokes. The next rotation of the crank does the "power" and "exhaust" strokes. 4 strokes total for a 4-stroke engine of course. Pretty simple on the bottom end because it just does the same dance twice. But the top end (cylinder head) does different things for each stroke. Different valves are open for each part of the dance.

If the ECU can only see the position of the crankshaft, it has no idea what position the top end is in. Granted, there are only 2 possibilities so long as the timing belt is installed properly. The ECU relies on the CAM sensor to ascertain the physical position of the valves. In other words, it relies on the CAM sensor to find out what STROKE the engine is on at the current moment. Without that signal the car will not start reliably. The ECU has no other way to infer the stroke information other than to guess. If the ECU guesses correctly, the car will start. If it guesses incorrectly (180 degrees out), it will be firing the spark plug and injecting the fuel at all the wrong times = No Start.

[msharifi]

And if your timing was off you would get a crank/cam incorrect allocation fault. Not a cam sensor implausible signal fault

I'm having same issue getting code below is the cam intake and exhaust off of cam chain tensioner or on the timing belt?
1 Fault Found:
17748 - Camshaft Position Sensor (G40) / Engine Speed Sensor (G28): Incor. Correlation
P1340 - 001 - Upper Limit Exceeded

[audi_s450501]

What was ever found to fix this issue that bmx672 had ?? My car has the exact same issue and I've checked the same things he had stated as well. I'm at a dead end. My only guess is the ecu isn't using the signal it's getting. New cam sensor. Timing 100% both belt and chain. Checked it 3x. Checked my wiring good 5v. I even went as far as swapping new sensor with my s4 one and it worked fine on that car.

[VAGlover]

I'm having same issue getting code below is the cam intake and exhaust off of cam chain tensioner or on the timing belt?
1 Fault Found:
17748 - Camshaft Position Sensor (G40) / Engine Speed Sensor (G28): Incor. Correlation
P1340 - 001 - Upper Limit Exceeded

Replace the cam sensor. I had an identical issue with my car last week.



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[audi_s450501]

I already did that didn't you read my post lol I even took a known good one off another car and tried it. Same problem

[audi_s450501]

I just went as far as to clip the wires at the ecu and at the sensor and run my own wires just in case. Wish me luck lol

[Charles.waite]

Did you try replacing the sensor though??

[:-)]

[old guy]

If you are getting a P0340 read this thread. Clicky click®

[audi_s450501]

I read all of that post. only thing that's different is I'm only getting a bad cam sensor code. Nothing else. If my adjuster was bad or sticking wouldn't I throw the same codes? I might jump 12+ to the vvt and see if it makes it happy.

[audi_s450501]

Did you try replacing the sensor though??


[:-)]

Yes I did already. Once with a brand new sensor and then another off my buddy's car just to make sure the new one wasn't bad lol no change at any time