My car is in right now to replace a CAM sensor, which my independent said is a fairly common fault. The part is fairly cheap, I asked if I should replace both. My car is a 2005, so I expect some part failures and I don't mind getting ahead of it,. Anyone go through this? Any advice?

The symptom was pretty straightforward, I was at a stoplight, my car started idling really roughly, the check engine light came on (I thought it was the dreaded vacuum leak), then the engine stabilized and I had no more problems.

I diagnosed it with Ross-Tech, my independent confirmed, but they aren't committing to changing both if switching the part out on the first doesn't solve the problem (fair enough, I hadn't thought that far ahead). I'm worried it's a connector not the part itself, or a wiring fault, but I suspect it's just the sensor. eBay had one for $89, I'll probably pay more through the independent but still it won't break the bank.

Anyone go through this? I can't even tell it's failed.

 

Update: wasn't the sensor, the cam is really doing something out of spec.

 

Hello @British ,
Did you clear the fault codes to see if they came back yourself, as they are both "Intermittent" faults, I would clear them first, then check for recurrence of same, then have a look at the VVT wiring, then the VVT solenoid itself, as for your year BEB engine the VVT's have o-rings that might need a changing, and or iirc, a screen or ports that might need a cleaning, that is depending on your mileage and or your oil change habits.

My 05 A8L W12 did this same fault a few times over the years, just an Intermittent issue, usually when I let the vehicle sit for a long period of time, like for a year last time, cleared the fault, and it hasn't been back, engine performs just as it should.

The VVT's control the advancement and retarding of the cams.

Johnny

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At a stoplight, the car rough-idled for a minute, check engine light came on. Later I pulled the codes, cleared them. Drove it for about 1/2 mile and light came back on. Took it to the independent, they replaced the sensor, cleared the code, it came back again.

Thanks for the pictures, I'll pass them along.

 

Thanks a million Johnny, I passed this along.

 

​@British ,
Being that you cleared the faults and they returned, and it is not the CPS, then I strongly suggest having a look at the VVT solenoid for the intake cam, as you faults are only related to the intake cam and not the exhaust cam, now this will require the removal of the valve cover for access, so while they are in there, I would definitely have a look at the cam chain tensioner shoe/pad first, if the pad is worn, or even missing, it will affect the CPS reading of the cam position, as the worn shoe/pad will not allow for the full range of the required intake cam travel for advancement and retardation, as the intake cam has a total range of 52° and the exhaust only has 22°, iirc, so in my thinking, a worn or missing shoe/pad affects the intake cam range more than the exhaust cam range, I saw this once online for an Audi W12, and had it on my dad's old Jag years back, and not so long ago on my son's past A6 4.2, the shoe/pad was gone, riding metal to metal, yet no adverse noise, he also had intake cam position error.

There are many other guides and tensioners that the timing chains of the W12 ride on, but being that you only have one specific cam in question out of the four, I think the others should be fine.

Johnny

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