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Help W/ Trouble Codes 12&21 '93 Es300


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Just came back from Lexus service. Check engine light came on yesterday. Technician read codes 12 & 21, report says RPM signal and Main O2 sensor signal left bank detected out of parameters. He recommended replacing the cap and rotor to start, and states "possible other issues, unsure at this time."

Of course I'm not happy that the solution is not clear, I paid $52 for 30 minutes of the tech's time for the diagnosis. But hey I got a free car wash. Not sure when the cap and rotor were done, but a tune-up with plugs and wires were done at 120k, I have 163k now. I assume the cap and rotor were done then, but could be wrong. The car idles and runs smooth, and my gas mileage is still very good. I know the cap and rotor change is cheap, I just thought I'd ask if anyone knows the codes or the potential culprit before going further. The adviser made no mention of the MAF or cleaning the throttle body or injector service or motorvac or anything else I can think of.

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Here is the answer to your problem.

Code 12 is RPM Circuit Signal 1. The distributor in the Engine Control system contains three pick-up coils (G1, G2 and NE), The G1 and G2 signal informs the ECM of the standard crank angle, The NE signals informs the ECM the crank angle and the engine speed.

Trouble area

-Open or short in GE and GE circuit


-Open or short in STA circuit


Diagnostic Chart

-Check the resistance of each pickup coils in the distributor. If it's NO GOOD replace distributor

-Check wires for open in harness between distributor and ECm -If it's NO GOOD replace or repair harness

-Check for air gap. If it's NO GOOD replace distributor

Code 21 is your main 02 circuit or main 02 sensor.

I would suggest to have lexus check out this problem.

JP Importz

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