2005 Cadillac STS saga

cadillac
sts

#1

About 10 months ago, my STS (with N* 4.6L engine) started throwing Cam Position sensor codes and was running terribly. Had to order a sensor and before it came in… broke a timing chain. This proved to be costly as it took out sprockets, bent valves, ruined a head, etc. After repair, it ran well for about 6 months. Would throw an occasional catalyst messages, then started throwing cam position sensor codes again. After the engine gets warm will start running extremely rough like it’s way out of time. When it starts running rough, I can shut it off and restart and it will run smooth again until 2000 RPM is hit then begins to run rough again.

I did find out that GM extended the catalytic converter for a VIN range that my car is in from 8yr/80,000 mi to 12yr/200,000 mi. Took it into the dealer, unfortunately it wasn’t throwing the catalytic converter codes at the time. Dealer says that they want to tear into the engine to look at a check valve between the block and the head (for $4000). Before it starts running rough, it runs incredibly. I’m at a total loss on what the problem could be. I’ve replaced cam position sensors. Don’t feel like spending $4000 so the dealer can tear into the engine when they say they don’t know if they’ll find anything. Waiting for the car to throw the catalytic converter code so they will replace them for free ($2500 if it wasn’t under warranty.) Normally will throw that code when tank is around 1/4 full… I know, that sounds ridiculous.

In the meantime, has anyone run into something like this? Could a problem like this be caused by the catalytic converters? Any other suggestions?


#2

I had the same problem except for ruining the timing chain. I had received a letter from Cadillac saying they extended the cat warranty to 12 yrs for 2005 Cadillac STS 4.6 liter. I took my car to Cadillac with the letter after I got the cam code and they replaced both cats. Runs great now. The service manager said to hang on to the letter in case it happens again.


#3

aproman, thanks for the comment. So you had the same problem in that the engine was running terribly after warm-up and replacing the cats corrected it? If so, that is FANTASTIC news to me, I just have to drive short durations until it throws the cat code so they will replace it.

You have given me great hope… I love my car, the funnest car to drive that I’ve ever owned. But I don’t want to spend 1000’s of $ chasing a problem.

Thanks again


#4

The code should still be in the computer, it will stay there until they erase it. I also used OnStar to get the code and forward it to my dealer.


#5

I had cleared the code while trying to diagnose the position sensor problem :frowning: So when I took it to the dealer it didn’t have the cat code so they could replace the catalytic converters… so I’m in the process of waiting for it to throw the code again. Your earlier comment that you had the same problem and it was solved by replacing the catalytic converter gives me great hope that it’s the source of my problem.

My belief is that the O2 sensor is seeing the mixture of being too lean because of the bad cat, the computer then richens the mixture to compensate causing it to run too rich, as a result the knock sensor then detects a knock then advances the timing making it run terribly (loss of power, knocking, smells terrible, etc), the computer then throws the position sensor failure. Basically, just a domino effect where the cat is the root cause… just a theory.