In the Chevy Tahoe, P0420 is often caused by a bad oxygen sensor, but there can be other causes as well. The code technically stands for: CatalySTSystem Efficiency Below Threshold.Your Tahoe has at least two oxygen sensors, one before and after the catalytic converter. Among the many jobs that oxygen sensors have is they have to measure the emissions levels coming in and out of the converter. When the readings from the upstream and downstream oxygen sensors show similar readings, the vehicle will throw the service engine soon light (P0420). Typically, the code will be triggered by the upstream oxygen sensor (before the converter).There arent usually any drivability issues associated with P0420. For most people, the firSTSign that anything is wrong at all is the service engine soon light coming on.
I replaced the oxygen denotes and bought a new air filter and cleans the sensor near it and it’s still showing 2 codes which is ap0420
Roger E.
April 9, 2020
A p0420 code on your chevy tahoe means there is a damaged or failed oxygen / o2 sensor. Or a downstream oxygen sensor (ho2s) has been damaged or connected improperly.
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