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Catalyst System Efficiency Below Threshold On 02 Corolla

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I have an 02 corolla (new shape) and recently my engine management light turned on and when i connected my laptop to the OBDII, i got a the following error code: PO420 Catalyst Efficiency Below threshold (Bank 1).

I changed the o2 sensor at the front and cleared the code from the ECU. I then drove it for weeks and the light never came back. Last week the light came back on with the same error code.

I noticed that both of the times when the error came up was when i had been driving with my AirConditioning on for a long time.

I've cleared the fault code once again on the ECU and am now driving without turning on the A/C and it hasnt come back yet.

Has anybody had this sort of problem? how could the A/C be effecting this?

Is there any way that i can test my CAT to see if its ok? my OBDII software lets me monitor the o2 sensors. I read somewhere that the 2 sensors can be monitored and if they give certain results, then it means CAT needs replacing.

Any suggestions would be appreciated.


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