Question about Chevrolet Monte Carlo
1st off, P0420 is not an O2 sensor code, it is a catalyst efficiency monitor code, this means when the measured limits allowed exceed a certain limit for the clean up of the exhaust gas stream the Powertrain control module (main computer control) will turn on the check engine light and store code P0420 to signal the Catalyst is worn out, this sensor looks like an O2 and is located after the main catalytic converter in the exhaust system, many factors can trigger the light to come back on, a defective sensor is possible and replacing the one sensor after the cat may cure the problem other factors that affect the cat performance are using an aftermarket catalytic converter and any type of exhaust leaks ahead of the cat converter, loose head pipes or leaking exhaust manifolds or rusted out pipes, anything that leaks ahead of the catalytic converter, so do this, replace the cat efficiency sensor aft of main cat and check for any type of exhaust leak before the main cat converter, if the code comes back an u did use a universal replacement that didn't come from GM that is the problem, and that is the common issue, aftermarket cats in many cases just don't clean up the exhaust enough to satisfy the parameters of the powertrain control module that constandly monitors the output of the cat converter, you can also read more about the rather confusing subject at the web link below, it is solely dedicated to the subject of OBD2 code P0420. the info i have just given u was learned at GM factory schools while i was a GM dealer tech, my speciality is electronic engine control .
Posted on Oct 18, 2010
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Posted on Jan 02, 2017
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