Since it started cooling off some here in No Texas I've had some odd behavior from the O2 sensor(s). When the ambient temperature drops to 53F or below (as read on the MINI temp sensor) I'm getting a P0420 code. I can easily clear the code and as long as the outside temp is 54F or higher I do not get the code. P0420 Catalyst System Efficiency Below Threshold Keep in mind that due to the RMW Race Header I use the leads on the O2 sensors had to be extended. Before I start pulling O2 sensors and swapping them out does anyone have an idea if it may be the front or rear sensor? Or have other ideas on why this is happening. I suspect the pre-heat circuit may be bad and when the temp drops below a certain threshold it kicks out the code. Overall drive-ability is not affected.
I have had odd 02 sensor readings. If I start the car in the morning, then turn it off right away, and restart it, one of the sensors throws a code. Drive-ablity is not affected, and it clears after 5 cycles. My solution is to not turn the car off till it gets to normal operating temps:idea:. Mark