2007 Cadillac SRX - P2099

Hello, I have been chasing a P2099 (Bank2) issue for quite some time now. The vehicle is a 2007 Cadillac SRX 3.6L Base. All the basic things related to fuel, air, sensors have either been checked out or replaced (I did find the lower intake manifold rear bolt completely backed out which I thought was the issue but did not make a difference). I have replaced O2 sensors, exhaust gaskets, injectors, gaskets, emissions control lines tuning valve. I have even replaced bank2 Catalyst with an Eastern Catalytic brand. What I am seeing right now is that the LTFT #1 is running (minus) - 4% and the LTFT #2 is running around 6.7% and is fairly constant over the speed range. There is some attempt to increase bank1 and lower bank2 over some extended driving, but very minor changes. The code comes up randomly between 70 miles and 200 miles. I do get black soot on the rear of the vehicle and must be cleaned which is telling me it's overfueling. Given that the right and left banks are opposite values, it might be pointing me towards the downstream exhaust. But, if the center resonator is a crossover (in otherwords the exhaust banks mix), then that might negate any downstream effects as both banks would be seeing the same backpressures. I wanted your thoughts on this and any advice on where to look and if something was missed in the process. O2 voltages are reporting similar values on bank1 and bank 2 post catalyst. As I said, please keep in mind all the standard checks have been completed but please feel free to ask.

What is a rough average for each Bank of ST1+LT1. and ST2+LT2 at idle and also at 2000 rpm ?

Another question had any major work been done the top end of the engine or inlet or injectors or engine harness before the fault appeared ?

Hi Andy,

The rough average of the ST1 is hovering around +/- 3% and LT1 is -4%. For ST2 the same and LT2 is +6%. These values remain stable thorughout the RPM range for the most part - very little variation. I do see some LT1/2 minor corrections that tend toward zero but not more than .25-.75%

No major work on the top end. I did replace the injectors and the upper/lower intake gaskets. Interestingly enough, while doing this I did find the lower intake rear bolt backed out completely. As you might guess, I thought I found the smoking gun....but to no avail.

I would be looking specifically for exhaust leaks, audible or not, between the upstream and downstream O2 sensors. Being a 2007, it probably has a few.

Hooking up the smoke machine is an option. Using light air pressure is another. You can also have a helper plug the exhaust with rags while you listen/feel around.