CEL P0171 and sensor questions...

[sethsterrr]

Hello. I have a 2003 Toyota Solara, equipped with the 2.4 liter 2az-fe engine, and it is in California so I imagine it is a CA model. I have been getting a CEL for over a year now. It is code P0171 too lean (Bank 1, Sensor 1). I have noticed that the car does have some spark knock at low speeds and uphill every once in awhile too. I have searched extensively on this forum and others, and it seems that most people say that the fix for this code is to either clean the MAF, or replace the 02/Air-Fuel ratio sensor.

As for the code P0171, I have tried the following to solve the problem with no luck:
-Cleaned K & N Drop in Air Filter
-Cleaned MAF Sensor with proper cleaner
-Checked for vacuum leaks by spraying TB cleaner around hoses
-Cleaned Throttle Body
-Replaced PCV
-Pulled out front Air/Fuel or O2 sensor on the radiator side to see if it had carbon buildup and it did not
-Cleaned the fuel injectors
-Changed Spark Plugs (needed them anyway), and all four plugs looked like they were healthy and they all looked the same

Everytime I reset the ECU, and the code comes back at around the 200 mile mark. I am trying to figure out which sensor is (bank 1, sensor 1), and whether it is an air/fuel ratio sensor, or an oxygen sensor. I have called Autozone, the local Toyota dealer, small Autoparts stores, and they all give me different answers.


Here are some pics:

Which sensor is this?


And which sensor is this?


And, is there another sensor after the catalytic converter? If so, which is it?


Does anyone have an answer to my questions or some guidance here? Any help is appreciated, thanks

[Qslim]

Your 4 cyl should have two sensors. The sensor in your last pic (the one with the hole in the heat shield) is bank 1 sensor 1. The following sensor is b1s2.

In my experience, air/fuel ratio sensors are rarely at fault for a 171 by itself. Usually the mass air flow sensor is the culprit. Also, P0171 should read "system lean, bank 1" without making a reference to a sensor #.

[sethsterrr]

Thanks! I just realized that my car has two catalytic converters. That explained it all for my two sensors as opposed to which one was which.

I didnt know what else to do, so I changed the sensor today. I cleaned the MAF 3 times with the MAF Sensor Cleaner spray, and every time the code comes back. I guess if the code comes back again I just forked out 125$, but I could always sell the part on ebay I guess.

I will let you know if the code comes back. Thanks for the help

[sethsterrr]

Just an update. I have driven approximately 1000 miles so far and no CEL anymore. I replaced the B1S1 with a Bosch brand one (not OEM). This must have fixed my problem.

The only other thing I did at the same time was clean and re-oil my K&N Drop in Air Filter, and then I cleaned the MAF after driving 100 miles or so in case any of the oil got on the sensor.

[elraido]

Originally Posted by sethsterrr

Just an update. I have driven approximately 1000 miles so far and no CEL anymore. I replaced the B1S1 with a Bosch brand one (not OEM). This must have fixed my problem.

The only other thing I did at the same time was clean and re-oil my K&N Drop in Air Filter, and then I cleaned the MAF after driving 100 miles or so in case any of the oil got on the sensor.

Odds are you over oiled your K&N the first time and it kept getting the sensor dirty. When you cleaned it, you added the right amount of oil. It is a common mistake.

[sethsterrr]

Originally Posted by elraido

Odds are you over oiled your K&N the first time and it kept getting the sensor dirty. When you cleaned it, you added the right amount of oil. It is a common mistake.

That would be true if that happened, but a K&N Drop-In Filter comes pre-oiled in the package.

And actually, the CEL has since returned with the same code after about 1500 miles driving.

[new echo owner]

The MAF sensor doesn't like the oil from those filters, it gets all screwy when the oil gets on the sensor; do a little experiment, go to the parts store and get a regular air filter, clean the MAF sensor and put some miles on it see if your problem comes back.

N.E.O.