Mechanics

ENGINE CODE P0420

2000 SAAB 9-5

Engine Performance problem
2000 Saab 9-5 6 cyl Two Wheel Drive Automatic 109000 miles

The engine light comes on and I get a fault code P0420. It seems to happen more often in the warmer weatherand in Sport mode. The engine has a dieseling type sound when the fault occures.
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Tcmatteson
June 23, 2008.



A code P0420 may 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 readings

Possible solutions suggested steps for troubleshooting a P0420 code include: 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

Rasmataz
Jun 23, 2008.