Actually, the fault code did not say the sensor was the problem. Fault codes never say a part is bad or it needs to be replaced. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a fault code, it is actually the cause of that code only about half of the time. First you have to check the wiring, connectors, and in some cases, mechanical problems that prevent a part from doing its job.
Without looking to check for sure, it is most likely your engine has four oxygen sensors. "V-type" engines have two "banks", meaning sides, and each bank has two sensors. Starting with all '96 models, the sensors just in front of the catalytic converters monitor the exhaust gas for its rich or lean conditions which switch about two times per second, just like they've done since the late '70s, but we've added another sensor at the back of each converter to monitor their efficiency. Those typically switch between rich and lean perhaps once every minute or two.
P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
This code suggests the oxygen sensor is working just fine and is reporting a bad condition. You need a scanner to view live data so you can see what that sensor is doing, but the most likely cause is a defective catalytic converter.
Sunday, July 5th, 2015 AT 10:15 PM