Code P0420 is a common code with many causes. It indicates a problem with the catalyst system. Follow this Real Fix to see how a mouse caused a problem with the cat system.
Vehicle
2000 Volvo S40 1.9L
Title
Code P0420, cleaned air cleaner housing.
Complaint
The customer states the check engine light is on.
Cause
Connected a scan tool and found code P0420 – Catalyst System Efficiency Below Threshold (Bank 1). Performed a road test with the scan tool connected to monitor live data and found the long term fuel trim and the short term fuel trim were out of range. Monitored the specified 2.2 to 3.1 BAR fuel pressure on the scan tool and found the measured fuel pressure was within specifications. Performed a visual inspection of the air intake system and found no apparent faults. Removed the lid for the air filter box, removed the air cleaner and found a rodent nest in the air cleaner housing restricting the air intake. Inspected the air intake, pipes and hoses between the air cleaner housing and the Throttle body for blockage and found no faults. Inspected the throttle body bore and the throttle plate and found no faults.
Correction
Cleaned the air cleaner housing, cleared codes, performed a road test and verified the vehicle operated properly. The check engine light did not illuminate and no fault codes returned.
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