'01 4Runner air/fuel ratio sensor keeps going bad?

[merlin417]

Air/Fuel ratio sensor was replaced at 15k, 21k and 26k miles anybody have any info on this? Also with 27K miles getting new main bearings.

[ToyotaTech]

At the dealer? I have never heard of this. why main bearings? sounds wierd.

[Brian R.]

Sounds like possibly someone messed up an oil change...

[merlin417]

All work is from dealer. I don't hear the knocking.The dealer heard it the last A/F sensor replacement. Anybody have any info on the A/F sensor?

[westca707]

How do you change the air/fuel sensor? I have an engine check light on. I changed the O2 sensor, reset the fuse. And still show a check light. Any suggestions?

[Brian R.]

A/F sensor is a modified O2 sensor - more sensitive, but fulfills the same function. You change them in the same way you do an O2 sensor. Some cars have O2 sensors, some have A/F sensors. Make sure you know which you have before you replace it. They are not interchangable.

[westca707]

How would someone know the difference?

[Brian R.]

You wouldn't. You have to ask a Toyota parts department to be sure. You don't have to buy one, just ask for the type of sensor, price and part number. You may need your VIN number to be sure. I have heard vehicles meeting California emission standards have A/F ratio sensors. Non-CA vehicles have O2 sensors. Best to check.

Price is for comparative purposes. If the Toyota price is close to aftermarket, I would go with a Toyota sensor. If you save alot by going aftermarket, then you have a difficult desision.

[ToyotaTech]

what codes are u guys getting?

[westca707]

Originally Posted by ToyotaTech

what codes are u guys getting?

Code #25

[Brian R.]

Air-Fuel Ratio Lean

Sounds like a bad O2 or A/F ratio sensor. westca, maybe you need to change sensor #2 behind the cat converter. If you have a CA emissions truck, you probably have an A/F ratio sensor.

[westca707]

Didn't know I had one other sensor behind the coverter. Thanks!

[Brian R.]

You're welcome

[bulletbarry]

Can anyone answer westca707's 5/19/2004 question?

"How do you change the air/fuel sensor? I have an engine check light on. I changed the O2 sensor, reset the fuse. And still show a check light. Any suggestions?"