RepairPal is your advocate for car care advice and guidance

Q: 2001 rx300 cel codes P0171 P0174 P1150 on 2001 Lexus RX300

cleaning the MAF didnt fix. syst too lean bank 1 bank 2, af sensor range performance bank 2 sensor 1. if both banks fuel trim out of range, why is only bank 2 sensor 1 setting a code? is the issue bad MAF meter or only the 1 af sensor?
Get a Repair Estimate
Guaranteed by certified locations nationwide. Learn more
RepairPal estimates are guaranteed at over 1,700 quality certified locations nationwide. Learn more
The worst bank will set the code first. I also find that cleaning the Mass Air Sensor to be ineffective, especially the type that a Lexus uses, which is based on the newer Bosch thin film Air Flow Sensor. About the only area that you can clean is the intake air sensor which does nothing to help you.
Refer to this article below that I wrote about how to inspect for a code P0171 and/or P0174. You must be able top SEE the Long Term Fuel Trim on the scan data, so if you are trying to diagnose this code with out any scan data, you will have a really tough time. The Long Term Fuel Trim is typically above 12 % for the code setting bank and the other bank may be close, but still under the code setting level, like 10% etc.
A code P0171 has NOTHING TO DO WITH a defective air fuel ratio sensor!!!! or a defective oxygen Sensor, they have to be passing their self tests to even set this code, this is a huge misconception most shops and Techs have.
So follow this article -> look for any vacuum leaks and then find find the long term fuel trim, if both banks are high ( like over 10-12% ) and pretty even, then the air flow sensor is suspect, IF you don't have vacuum leaks. Also if the air cleaner is pretty dirty or if the air box for the air cleaner is pretty dusty, that will wipe out the air flow sensor, because the dust sticks to and ruins the thin film sensor. I recommend cleaning the air cleaner box and replacing the air cleaner every 12 mos or 12k miles, minimum. It saves your Mass Air flow Sensor big time.
thanx for ur technical knowledge. out of mental process of elimination and 2 weeks of trying to comprehend obd codes and DIY posts, i replaced the MAF, since cleaning didnt clear codes P0171 P0174 P1150. and was suspect. the air box and filter were clean, like new, and no vaccum leaks. Ive preformed several test runs to recreate the malfunction scenario, with success. codes have not reset, only time will tell. why those codes set and not codes pertaining directly to the MAF itself still puzzles me. i guess id have to work on cars everyday to have a better understanding, and a scanner for spec data would help immensely. right tool for the right job. almost bought a scanner so i could get first code that was set, but wanted to research the best avail for retail without much success. Autozone scanned codes and gave me a small printout of each code with description. im a systems tech by trade and do constant troubleshooting on a daily basis.if u have a recomandation for a decent low price scanner, please post! thanx again, u were very helpful and professional and assisted me in my final diagnosis. A+++++
fix update
i cleared all codes, drove till the cel came back on, went directly to Auto Zone, two codes now. P1130, P1170. those are a/f sensor range malfunctions bank 1 sensor 1, bank 2 sensor 1. i cant read the fuel trim and am not just gonna change parts, so i took it to a local shop. first they changed the MAF, i told them i already had changed it and it wasnt the isssue, so he told me at Toyota training, they said if u get one a/f sensor error and replace the designated sensor, the opposing sensor will go out and your cust will be back, so they advised to replace both sensors. i told him to change both sensors, put in the old MAF, and test drive to see if it needs the new MAF. long story short i didnt need the MAF, to clear cel he said he had to dive it a "global" clear, something u have to do after an engine/trans change and so far so good. damn the stupid sensors are expensive. what are they made out of gold, ha ha. what a pain. glad im not a mechanic, these newer sensor cars suck to diagnoss. i could barely even see bank 1 sensor 1, must have been fun to r&i. thats why i paid $566.00
Didn't find what you were looking for?