P0420

Tests 354 - 358:

SYMPTOM
P0420 - 1/1 CATALYTIC CONVERTER EFFICIENCY

WHEN MONITORED
After engine warm up to 170 °F, 180 seconds of open throttle operation, at a speed greater than 20 mph, with the engine at 1200 - 1600 rpm and MAP vacuum between 15.0 - 18.0 in.Hg.

SET CONDITION
As catalyst efficiency deteriorates, the switch rate of the downstream O2 sensor approaches that of the upstream O2 sensor. If at any point during the test the switch ratio reaches a predetermined value a counter is incremented by one.

POSSIBLE CAUSES
- Engine mechanical problem
- Exhaust leak
- Catalytic converter 1/1 defective
- Upstream O2 sensor older than downstream O2 sensor
- Catalyst efficiency failure does not reoccur