nbaptist

On my 2000 Camry I get an intermintent check engine light! It will stay on for 2 to 4 days and off for up to 2 weeks so it was diffacult to catch it when it was on!

I get the P0420 Catalytic system efficiency below threshold. It this a serious problem? I am confused due to the fact that the light will turn off for around 2 weeks before comming back on! Could it be the O2 sensors as I have just 100K on the vehicle and do alot of distance driving and not many short trips!

Thanks

Neil

Swamp Donkey

if you have no codes for the o2 sensors then they are fine. try using a higher grade of fuel for a while.if that doesnt fix your problen then you will need new converters

Brian R.

Yes, it could be the HO2 sensors. The ECM determines that you have a problem with the catalytic converter by comparing the signals of the two HO2 sensors, before and after the CC. If one or both the HO2 sensors are bad, you will get a P0420. Replace these before you replace the CC. Much cheaper. 100k is a reasonable life span for the HO2 sensors.

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nbaptist

Brian,

Thanks I will find out about the parts. One question, if th O2 sensors are bad wouldn't the CEL stay on all the time, for that matter if it were the converter wouldn't the CEL stay on all the time for the same reason?

Thanks

Neil

Brian R.

Take your VIN to the dealer to make sure you get the right sensors. There are at least two possibilities.

As far as the CEL staying on, anything is possible. Both the CC and the HO2 sensors are judged by the same signal. If the CC is bad and the HO2 sensors are both good, you would expect the light to stay on (but this is not a law of nature).

Depending on what is wrong with the sensors (if anything), you may be able to test them on the car before you replace them. If you have an intermittent problem, you are screwed unless you happen to catch them malfunctioning.

See: http://www.autoshop101.com/forms/h37.pdf and http://www.autoshop101.com/forms/h64.pdf

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Toysrme

Replace the post cat sensor, then replace the cat.

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