P0420

Description
TWC SYSTEM LOW EFFICIENCY

Three-Way Catalyst (TWC) system is used to control emission.
PCM uses signal from Heated Oxygen Sensors (HO2S) to read efficiency
of TWC. PCM will set DTC P0420 if TWC oxygen storage capacity is less
than a predetermined threshold.
Symptoms
You will likely not notice any drivability problems.

Causes

• An oxygen sensor is not working properly
• The engine coolant temperature sensor is not working properly
• Damaged or leaking exhaust manifold system
• Retarded spark timing

Possible Solutions

• Check for leaks in the exhaust system, manifold, pipes, catalytic converter. Repair as required.
• Use a scanner to test the O2 sensor for proper wave form.
• Inspect the oxygen sensor, replace if necessary
• Replace the catalytic converter