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I was told it means to replace the cat. Now my car shuts off without notice. And is very difficult to get started, I mean I have to start it 4 to 5 times to get it started and give it a little gas to keep it idle. I have changed the ICM 1 coil both vent solenoids MAF sensor down stream 02 sensor. What are the symptoms of a plugged cat? Because I dont want to change it and it doesnt resolve the problem

How many miles on your car?

Code 420??

lol...

Sounds like some sort of smoking problem.



Craig

PO420 lol

Three-Way Catalyst (TWC) system is used to control emission.
PCM uses signal from Heated Oxygen Sensors (HO2S) to read efficiency
of TWC. PCM will set DTC P0420 if TWC oxygen storage capacity is less
than a predetermined threshold.
That what the code means so. IT could be cat, but it also could be a 02 sensors. it also could be leak in exhaust .
It should actual be safe to drive the car like that, but if was bad 02 you would get poor fuel milage

150,000 miles..... the code is P0420 I just figured everyone would know that... I also meant to ask would a plugged cat cause a car to just shut off without notice... Does anyone know how to change an UIM? If so please send pics

http://www.pontiacbonnevilleclub.com/fo ... c1061.html

http://www.pontiacbonnevilleclub.com/fo ... c3591.html

a bad rear O2 sensor will not make a car fail to idle. my guess is the cat is plugged. you can start by unbolting it and inspecting it to see if it is obviously melted inside. try unboltin the flange just before the cat and see if the car will idle/run with the downpipe unhooked from the cat. will be loud but should idle fine. if you have a lazer temp gun you should be able to see a 100-150* increase in temp from the front of the cat to the back, if it doesnt then again i would say the cat is the issue.

If it is then i would suggest a 2.5" ZZP downpipe, might as well upgrade while fixing it.

Z