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Obd Readiness Monitor


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Would appreciate help in trying to understand some workings of the computer controlled processes on my 2000 RX300 to aid in current self diagnosis. I know there is a lot of expertise on this forum.

What conditions or how many cycles does it take to reset a "not ready" to a "ready" code on an OBDII monitor?

I had a trouble engine light activate. Borrowed an OBDII scanner from Auto Zone and read a P0171 code.(System too lean). Not willing to invest in an O2 sensor untill positive that is the problem, I cleaned the MAF sensor and reset the trouble code. My thought was that if a dirty MAF sensor is reading low, it is sending a low feedforward signal to the computer thus not calling for enough fuel. The O2 sensor, seeing a lean mixture, then cranks up a feedback signal to increase fuel, and the OBD interprets this as an out of range signal. This is strictly an inexperienced guess, so could one of you let me know if this is a possibility?

I reset the trouble code and then switced the meter to read the I/M monitor readiness codes. It stated the O2 sensor not ready. Does this normally happen after a trouble code reset? I took the car through about five short cycles and the not ready condition continued. Should it have reset to ready by then? I had to take the meter back so I do not know if it is still "not ready" Could this be keeping the trouble light from coming on, therefore giving me a false hope that I fixed the problem? The trouble code has not activated as of now (approximately 12 cycles) I am due for a smog test next month and want to make sure there are no surprises then.

Thanks for any information and education anyone can provide.


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The o2 sensors must be hot before they will register any value with the ECU . Until then it just runs in open loop and bypass the sensor.

There a a few threads witht eh similar problems which should help you quite a bit on fixing it faster and cheaper.

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