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I got a code P0420 on my car yesterday (scanned at Autozone). I guess it has something to do with the cat. BUT, I have an RT cat, bought it used, but it looked really good before the install. Could it be the O2 sensors just going bad?

The car drives fine, no hesitation or what not. I disconnected the battery to undo the code, to see if the code will come back. So far, it hasn't (knocking on wood).

Help guys! I don't like CELs.

marc
 

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P0402 - EGR Flow Excessive Detected The EGR system is monitored for undesired EGR flow during idle. The EGR monitor looks at the DPF EGR signal at idle and compares it to the stored signal measured during key ON and engine OFF. The test fails when the signal at idle is greater than at key ON engine OFF by a calibrated amount. EGR valve stuck open
Plugged EGR vacuum regulator solenoid vent
Plugged EGR tube
Slow responding D.P.F. EGR sensor
Damaged DPF EGR sensor
Improper vacuum hose connection
Plugged vacuum hoses
EGRVR circuit shorted to ground
Damaged EGR vacuum regulator solenoid
Damaged PCM
A DPFEGR PID reading that is greater at idle than during key ON and engine OFF by 0.5 volt or a rough engine idle, may indicate a hard fault.
 
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