P0420

P0420-CATALYST EFFICIENCY (BANK 1)







- When Monitored:
After engine warm up to 70°C (158°F), 180 seconds of open throttle operation, at a speed greater than 18 mph and less than 55 mph, with the engine at 1200-1700 rpm and MAP vacuum between 15.0 and 21.0 inches of mercury (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. Three good trips to turn off the MIL.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. ACTIVE DTC

NOTE: A new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set. Review the repair history of the vehicle before continuing.

NOTE: If an O2 Sensor DTC set along with the Catalytic Converter Efficiency DTC diagnose the O2 Sensor DTC(s) before continuing.

NOTE: Check for contaminants that may have damaged the O2 Sensor and Catalytic Converter: contaminated fuel, unapproved silicone, oil and coolant, repair necessary.

1. Ignition on, engine not running.
2. With a scan tool, read DTCs.

Is the DTC active at this time?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. VISUALLY INSPECT CATALYTIC CONVERTER
Inspect the Catalytic Converter for the following damage:

- Damage Catalytic Converter, dents or holes.
- Severe discoloration caused by overheating the Catalytic Converter.
- Catalytic Converter broke internally.
- Inspect both ends of the converter, inlet and outlet.
- Leaking Catalytic Converter.

Were any problems found?

Yes

- Replace the Catalytic Converter. Repair the condition that may have caused the failure.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 3

3. CHECKING THE EXHAUST SYSTEM FOR LEAKS
1. Perform the diagnostic procedure for CHECKING THE EXHAUST SYSTEM FOR LEAKS. Checking the Exhaust System For Leaks

Were any problems found?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go to 4

4. ENGINE MECHANICAL CONDITION
1. Check the exhaust for excessive smoke caused by an internal problem in the engine.

Is an engine mechanical condition present?

Yes

- Repair the engine mechanical condition as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 5

5. AGING O2 SENSOR
1. A new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set.
2. Review the vehicles repair history.

Has the rear O2 Sensor been replaced without replacing the front O2 Sensor?

Yes

- Replace the Front O2 Sensor as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 6

6. CATALYTIC CONVERTER

If there are no possible cause remaining, view repair.

Repair

- Replace the Catalytic Converter.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test