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Check Engine Light On

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I was driving my car and the check engine light turned on. I reset it and after 15 miles it came on again. So I went to Autozone (they check it for free) and the OBD code was P0172. Car is a 98 GS400 60k Miles, with K&N Filter. I just bought the car a week ago.

Their computer readout said "The fuel system for Bank 1 was too Rich. (bank one identifies the location of Cylinder #1, While Bank 2 Identifies the cylinders on the opposite bank."

The guy at autozone said the O2 sensors might be bad. O2 sensor ran $180 each.

I've checked and Chilton does not make a manual. So I went to ebay and bought a Lexus CD service manual. (waiting for it to arrive)

Has anyone else had this problem? I would like to fix it myself because I've done it in all my cars. I had no drop in fuel mileage, and the car accelerates just fine and no hessitation. Idles at 500RPM> Is that normal?

I've done a google search for P0172

Code P0172 can be caused by several problems:

1) Fuel line pressure

2) Injector Blockage

3) O2 sensor malfunction

4) Manifold absolute pressure sensor

5) Engine coolant temp. sensor

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From your list, the O2 sensor is the most likely source. They go due to the high heat / cooling cycles.

In a distant second in line would be the coolant temp sensor followed by possible clogged gas filter (rare).

My GS400 has about 80k but nothing has gone wrong yet.

I'm no expert, just been around this for a while.

If it was my car, I would not do anything for a few tanks of gas and see if the problem goes away. Then replace the O2 sensors.

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