2000 Mazda Protege P0420 TROUBLE CODE

WEBER1954

MEMBER
2000 MAZDA PROTEGE

2000 Mazda Protege 4 cyl Front Wheel Drive 160000 miles

I live in Tennessee and all cars must pass emissions before they can be tagged. Well on the first trip we failed due to a a code 1141 which said O2 Sensor Bank 1 Sensor 2. So I replaced the sensor and when the test was done the second time it said Misfire at cylinder 1. So I replaced pluggs and wires and got rid of that code. Now it gives me a code of P0420 "Catalyst efficiency monitor malfunction- Bank 1" now all other codes are gone but I am confused as to why when the car is running great I get all these additional codes that were not a problem before. Any help would be greatly appreciated. I don't want to end up spending an arm and a leg just to tag my car. Thank you in advance. Oh and what is the drive cycle as far as miles to complete through the test period?

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

DTC P0420 could mean that one or more of the following has happened:

Leaded fuel was used where unleaded was called for
An oxygen sensor is not reading (functioning) properly
The engine coolant temperature sensor is not working properly
Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
Retarded spark timing
The oxygen sensors in front and behind the converter are reporting too similar of reading

Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
Inspect the downstream heated oxygen sensor (HO2), replace if necessary
Replace the catalytic converter