P0420
DTC PO42OCATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (CAT)
Description
- The Three-Way Catalyst is an oval shaped honeycomb monolith ceramic. Its porous surface is coated with platinum and rhodium.
- The catalyst is used to reduce HC, CO and NOx in exhaust gases, and permits simultaneous oxidation and reduction.
DTC Detecting Condition
Immediately at fault recognition
Trouble Symptom
- Engine stalls.
- Idle mixture is out of specifications.
1. Check any other DTC, PO13O, PO133, PO135, PO136, PO139 and PO141 on display.
[CHECK]: Check that Subaru Select Monitor or the OBD-II General Scan Tool shows P0130, P0133, P0135, P0136, PO139 and PO141.
[YES]: Inspect the relevant DTC diagnostics chart.
Inspection of PO42O is not necessary after above.
[NO]: Go to step 2.
2. Check exhaust system.
- Check for gas leaks or air suction caused by loose or dislocated nuts and bolts, and open hole at exhaust pipes.
[CHECK]: Check the following positions of exhaust system.
- Between cylinder head and front exhaust pipe.
- Between front exhaust pipe and front catalytic converter.
- Between front catalytic converter and rear catalytic converter.
[YES]: Repair or replace exhaust system.
[NO]: Go to step 3.
3. Check rear catalytic converter.
a. Separate rear catalytic converter from rear exhaust pipe.
[CHECK]: Is there damage at rear face of rear catalyst?
[YES]: Replace front and rear catalytic converters.
[NO]: Go to next step.
b. Remove front catalytic converter.
[CHECK]: Is there damage at rear face or front face of front catalyst?
[YES]: If there is damage in front catalyst, replace front Catalytic Converter.