The "SERVICE!" warning came on in my recently purchased A4 ('02 1.8T Quattro; my first Audi), so I took it to a mechanic who has taken care of a friend's Audi for years. Based on my friend's experience, I trust him completely, both to tell me the truth and to fix whatever the issue is properly without charging me for unnecessary stuff, etc. That said, his schedule is currently busy enough that he can't take it to work on it for over a week.

When he plugged his laptop into it, it returned with an error about the intake cam timing being retarded from where it should be. I didn't want to stick around and bother him too much about exactly what could cause that, etc, so I just confirmed with him that I wasn't going to smash my valves into my pistons, etc, and that it was therefore ok to keep driving it until he could fix it. I then set up an appointment and went on my way.

The question I have for all of you experts is this: what would the likely cause(s) of this issue be, and what real-world consequences does it have? I would imagine a slight reduction in power and/or fuel economy, but not much else. Is it possible this could have been caused by the previous owner running 87 octane when s/he should have been using 91 or better, or does it only impact ignition timing when the engine detects low-octane gas? (I feed it only 91 or better.)

Any insight would be appreciated, just from the perspective of me being the type of individual who likes to learn things. It doesn't seem to be running poorly or getting particularly bad gas mileage. Right now, I average in the neighborhood of 25-27 MPG depending on the mix of city & highway, and how aggressively I choose to drive.

 

I think that's your camshaft position sensor, is like 90 bucks to replace.

 

So basically, your thought is that the engine is working fine, but just thinks it's not because that sensor is faulty? I'll certainly be relieved if it turns out to only be a fairly inexpensive part that needs to be replaced.

 

Yes, but run the codes to confirm it might not be safe to drive your car like that, you might also want to confirm with a mechanic.

 

Already did that; like I said in the first post in the thread, the mechanic says it should be safe to drive it for now, and I have an appointment set up to get it taken care of in the not too distant future; he just couldn't get to it immediately. (There were probably 20 different Audis there between the ones parked outside and in service bays, so it sure seems like they're busy. It's kinda wacky to walk into a place and have an A6 above your right shoulder with its engine and front suspension sitting on the ground below it. )

 

Cool, so it seems like you're on the hands of a pro then. Good luck.

 

Well this is goofy. After the mechanic read and cleared the error about the retarded cam timing, the service light came back on immediately. My assumption was that it would be throwing the same error, but after dropping the car off with him, he called later in the day to say that that wasn't it, and that apparently the cam timing is fine. The new error is something with the secondary air injection, which is apparently hard to track down but noncritical.

My understanding is that it mainly has to do with improving the emissions performance of the car. He's trying to track down what the cause is, but we've agreed that it's not worth going nuts over. If he finds a hose that needs replacing or something, great; if not, I'm not going to worry about it for now.

 

Well, turns out the SAI fault was caused by a cracked vacuum hose, which he replaced. Hooray for my car now saying "OK," rather than "SERVICE!" when I turn it on! Happy to have it back; hopefully it'll now be problem-free for a while. Total cost with labor + an oil change was pretty reasonable IMO at just under $150. (I had just recently purchased the car, and the service records I got with it didn't indicate an oil change having been done anything remotely like recently, so I got that done just to be safe.) I'm sure the dealer would have charged me a lot more.