I'm getting a code 25 - 'air/fuel ratio fault' for my '95 sc400.

I've replaced the exterior fuel filter and removed, cleaned and replaced all injectors to no avail.

Any suggestions as to the cause. The car runs crappy with very low power and really rough around 40mph.

Thanks for any input.
sch.

 

Hm check the maf sensor yet?

 

No haven't checked maf sensor yet.

Was actually thinking o2 sensors first.

The poor performance begin a month ago about 30minutes after filling up at an Arco gas station.

 

Yea good idea. Probably the main o2 sensors.

 

Any ideas on where the O2 sensors are and how to test them?

I recently acquired this car, haven't picked up any manuals as yet.

sch.

 

I would say fuel.........being how coincidental that it started after fueling up....

 

Hey Kramer, thanks for your input.
I've emptied the tank on several occasions since, used fuel additives and different fuel types (shell, texaco, etc.) and grades, but noticed no difference.

This list suggests O2 sensor fault at https://www.clublexus.com/forums/sho....php?p=3727890

Any ideas on locating and testing the O2 sensors? I can probably find them, I just don't know how many and where exactly they are located in the exhaust system.

sch.

 

I belive your 95 obd1 sc400 has 4 o2 sensors. 2 main and 2 sub. I know it has been discussed before, so try a topic title only search in the sc forum for "oxygen sensor".

 

I had a 25 and replaced the two main sensors, the code never came back.

I tested them looking at the waveforms using a Toyota scan tool, both sensors seemed to read ok but very sluggish.

The sensors are located in the exhaust manifolds. If you take the front wheels off and look through the wheel well, you'll see the sensor, one on each side of course. The best way I've found to revome them is with a 22mm box end wrench going through the wheel well. The sensors are very long and most o2 sensor sockets won't fit over them.

KC