Hey all, I have an 09 Lexus GS460 in with a P0171 and P1170. Mostly focusing on the P0171 as of right now, I have a strong feeling it's causing the 1170. Might be wrong. I'm not sure, that's why I'm here. Started out by driving the car, car drives really good, has a slight stumble at idle, but nothing major. Pulled up fuel trims on my Modis and found Bank 1 STFT to be +20 and long terms to be about +15. Revving the engine, and driving the car under load didn't do much to change those numbers, but they did fluctuate back down to normal and then sometimes to around -10. Didn't seem to be anything super consistent with it. Bank 2 that's not setting a code has LTFT at a -2% (ish) but the STFT hangs around -10. I started off by watching my MAF g/s and calculated load, and on a snap throttle, the MAF goes up to 170 g/s and the calculated load goes to 97%. Not worried about either MAF at this time. What I did notice is that this car uses wideband O2s on the upstream. After consulting service information, and gathering the needed description and operation, I found that these sensors when running properly typically hang around 3.3 volts, and that they switch opposite to conventional O2's with 3.4+ being lean, and 3.2- being rich. So I added those PIDs to by data list, and found that the B1 sensor reads a steady 3.5, and B2 reads about 3.2. During driving, I noticed that when I gave her the beans so to speak, both sensors dropped down below 3 volts indicating that they were reading the enrichment, but the B1 didn't drop anywhere near as low as B2. Infact, it was quite rare for B1 to go below 3 volts at all. I also noticed that on decel, both sensors peg at 5v, I assume because the computer is cutting injector pulse, and that would indicate a normal condition in my opinion. Again, maybe I'm wrong. I'm not sure. I did find the A/F sensor to be oil contaminated (not severely but still) from a leaking valve cover. So at this point, I had decided that it would be best to start by replacing the B1 A/F sensor. However when I went into Mitchells estimate guide, it said that the job pays 17.7 hours because the engine and transmission have to be removed. This made me nervous, so I decided to take some things apart and perform some visual inspections on the motor. I removed the B1 air filter and intake boot, and inspected for cracks. None found, however there was a small amount of oil in the boot and throttle body. I also pulled the MAF to check for any contamination on the resistors and found none. I reassembled, and decided I wanted to drive the car again, so I pulled up my data stream and alas.. The STFT on B1 is now in the negatives correcting as if a problem has been solved. This was the end of my initial hour of diag, as well as the end of my day, so I decided to let the vehicle cool down, and I want to see what the trims look like in the morning. I still would appreciate any guidance that anyone has as this is my first time ever dealing with A/F sensors. My fear is obviously misdiagnosing the vehicle with such an expensive problem, and wasting my clients money. I do know that Identifix has a few hits for these sensors causing the P0171, but I'm always weary of anything I see on there.
Thank you for taking your time to help! It is always appreciated.
Topic Author
