Bad CPS w/o symptoms?

[DenverA4]

2004 A4 1.8t. Keep getting code P0340 - cam postion sensor circuit. Car starts right up every time, no misfiring, no stalling. Only symptom is it seems to lack power from a stop when cold - like really bad turbo lag. Otherwise it runs fine. Timing belt marks are perfectly alinged. I hate to spend over $100 for a sensor when my gut tells me that a bad sensor would cause more symptoms. Anybody had a bad sensor with so few symptoms? Other ideas?

[BARRY]

cam position? or crank? if your have really bad turbo lag feel that is probably due to the sensor not allowing the ecu to know where or how much to advance the intake camshaft.

[DenverA4]

The code says cam sensor if I google it.

[Dubsport Inc]

The code says cam sensor if I google it.

Yes you are correct...
http://wiki.ross-tech.com/wiki/index.php/16724/P0340
Have seen a few fail... check wiring first. What bothers me is you "should" have extended cranks times...

[walky_talky20]

Have you cleared the code? How quickly does it come back? I'm thinking that VVT operation may be disabled with this code set. Not sure. I know the VVT activates right at take off. My VVT tensioner would make a grinding noise during activation and it would always do this right at take off from a stop light, etc. This might cause somewhat less torque availability at that time, if the VVT is disabled.

[DenverA4]

I've cleared the code many times. Used to come back in a week or so. Now basically at the next start. It's weird b/c I participate in MB forums and the CPS itself is a common problem. Here it seems to be rare, and can usually be traced to timng or wiring insted. Wiring going bad surprises me as a common issue. But if the wiring were truly bad, woudn't I have more symptoms? If I unplug it, the car won't start all, so cleary the wiring it is doing something.

[DenverA4]

And speaking of wiring, I've tried to trace it but can't really tell where it goes. There are five colored snap connectors below the coolant reservoir - blue, orange, white green and black from left to right. Any idea which has the three wires from the CPS?

[Charles.waite]

Blue and green are knock sensors. White is the Engine speed sensor. Black is front O2 I think and orange might be rear O2. I know the CPS connector is bundled with the fuel injector harness, I'm not sure it connects at the back of the bay, It might go straight to the ECU.

And CPS failures are pretty common here. I think they're common with almost any car really...

[DenverA4]

I found a Bosch sensor at Groton for $47, so I'll put it on when it arrives and see what happens. I'll report bacl to hopefully add some knowledge to this topic that can be hard to diagnose.

[BARRY]

its a german car...all the sensors eventually go to shit. good luck with the new sensor, i carry a spare with me just in case.

[walky_talky20]

A crank sensor might make sense to keep on hand, but a 1.8T will run just fine with no cam sensor at all. It may take a few attempts to start, but it will start and run just fine. I ran my 1.8T for a week without the cam sensor even plugged in.

[DenverA4]

Just to update the outcome. I put on a new sensor, knowing it probably would not help. It didn't. Took it to an indy place I trust and they found the timing belt was off one tooth despite the marks looking perfectly aligned to me. The belt was installed by a dealer 20k miles before I bought it, so who knows. The one tooth off thing seems to be common on these cars. Weird.

[Nikoo0]

My main relay in the computer box went bad and through the same code. Along with other problems and codes. Once I changed the relay and reset the it has yet to come back. Relay number 219 was a 50 dollar relay from Audi