Hi, I got a check engine light the other day that turned out to be a P420. It ended up being that the converters are not working up to peak performance based on research and having the code checked.

I talked to my mechanic and we put it on the lift. It is a aXJ6, dual exhaust. It comes down off the manifold, into the two converters, then past the sensors and out past the secondaries.

My mechanic swears the problem is with the converters before the sensors just under the engine. I've started pricing them and they are not cheap. I had the code cleared and it takes about 2 weeks of driving, for me that is about a tank and a half, for the check engine light to come back on.

A couple of things about this causes me pause.

1 - I don't normally see check engine lights that take this long to re-trigger once there is a a problem.

2 - Is there any possibility that a fixing the front converters will not correct the code?

does any of this sound fishy to you guys? I would love your input.

thanks,

 

I had a 95XJ6 and had both codes and they cleared but this feedback could help you. See if this post helps P0420 & P0430 Codes - Jaguar Forums - Jaguar Enthusiasts Forum

 

This information should help you with troubleshooting your O2 issues Link O2Sensor OBDII PID Sensor I hope it helps.

 

The p0420 code is normally caused by degraded converters.Assuming that the rear o2 sensor (catalyst monitor sensor) is switching properly, then replacing the catalytic converter on the bank indicated should take care of the problem.Yes, this is a very expensive repair.

 

I had a 96 and when this happened, I replaced the first O2 sensor, this fixed the problem. Everyone said to replac eth esecond one but I took a chance and turned out right. I just couldn't resolve in my mind how the mixture could be controlled by a sensor working after the cats.

 

The rear 02 sensor is not used to control the air/fuel mixture.This sensor is used by the computer to monitor the effectiveness of the catalytic converter for emissions reasons.If the 02 sensor does not switch in a specified manor, then the computer sets a code p0430/p0420 (depending on the bank that is in error) to tell us that it sees a problem.This code can be caused by a few different factors.

 

Gus, that first thread was specific to the X-300, I believe, which uses the front and rear sensors differently.