Having problems with your 2001 Chevrolet Monte Carlo ?

PO420 CATALYS INEFFICIENCY BELOW THRESEHOLD BANK 1.REPLACED CAT, 02,?

Posted / edited by AnonymousUser on : 17-09-2018

Answers :

The PCM copares switch rates between the front O2 sensors and the downstream catalyst moniters. The catylist moniters are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called.\012
\012By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust. \012
\012If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, and sets a P0420, or a P0430, depending on which bank it is. \012
\012To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely. \012
\012If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you proabably need a catalytic converter. \012\012\012
\012You can try resetting the ECM by turning your ignition to the on position (engine not running) and pulling the fuse to your ECM for 30 seconds and then placing it back in. Once the fuse has been reinstalled, start the car and let it idle for 1 min and then go for a test drive.\012
\012The engine may stall when you restart it, let is stumble and stall. Just restart it, the ECM is relearning the sensors like it was the first start up the engine ever had then go for a test drive. \012
\012This should reset everything and turn your check engine light off, if the check engine light came back on, have it scanned again at Auto Zone, Parts source where they scan free of charge and address the issues the DTC codes points out. \012
\012The easiest thing to do first is a visual check of things. Visually inspect the exhaust system for leaks, check the catalytic converter for dents, holes, severe discoloration, and check for a rattle inside. If any of those syptoms are there, the converter likely needs replacement. \012
\012Then, visually inspect the downstream O2 sensor (behind the converter). Check for broken wires, obvious faults, etc. If all that checks out, you'll want to check the operation of the O2 sensor. To do that, you'll need access to a scan tool or oscilliscope. Check that the waveform is pretty steady. If the reading fluctuates then the sensor is likely bad and will need to be replaced as mentioned earlier.\012
\012Thank you for using Fixya and be safe.
Repair Help & Product Troubleshooting for 2001 Chevrolet Monte Carlo

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