P0420

P0420-CATALYST EFFICIENCY BELOW THRESHOLD
For a complete wiring diagram, refer to the Wiring Information.
Theory of Operation

The After treatment Diesel Oxidation Catalyst is designed to react with hydrocarbons in the exhaust stream, this chemical reaction reduces hydrocarbon emission levels and also produces heat. Periodically, the Powertrain Control Module (PCM) will utilize the heat generated by this reaction in the After treatment Diesel Oxidation Catalyst to actively regenerate and clean the After treatment Diesel Particulate Filter. This diagnostic checks that the After treatment Diesel Oxidation Catalyst is present and functioning correctly. The PCM monitors the efficiency of the After treatment Diesel Oxidation Catalyst for DD and DP models through interpretation of data received from the After treatment Diesel Oxidation Catalyst inlet and After treatment Diesel Particulate Filter inlet temperature sensor. For DJ and D2 models the DOC inlet temperature is calculated by the PCM, the monitor checks for a temperature rise across the After treatment Diesel Oxidation Catalyst. The PCM will set the fault if it detects that the After treatment Diesel Oxidation Catalyst is not present in the after treatment/exhaust system. The PCM will illuminate the MIL lamp when the monitor runs and fails in two consecutive trips. The PCM will turn off the MIL lamp immediately after the diagnostic runs and passes.

- When Monitored:
This diagnostic runs when the engine is running, and performing an active regeneration of the After treatment Diesel Particulate Filter.

- Set Condition:
The Powertrain Control Module (PCM) will set the fault if it detects that the After treatment Diesel Oxidation Catalyst is not present in the after treatment/exhaust system.





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

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

Are any other DTCs Active?

Yes

- Repair other DTCs before proceeding.

No

- Go To 2

2. CHECK FOR THE AFTERTREATMENT DIESEL OXIDATION CATALYST MISSING
1. Check the exhaust system to see if the Diesel Oxidation Catalyst has been removed.

Is the Diesel Oxidation Catalyst present in the system?

Yes

- Go To 3

No

- Replace the Diesel Oxidation Catalyst
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

3. CHECK FOR AN EXHAUST LEAK
1. Perform the CHECKING THE EXHAUST SYSTEM FOR LEAKS diagnostic procedure. Checking The Exhaust System For Leaks

Are leaks found?

Yes

- Repair or replace as necessary.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 4

4. EXHAUST TEMPERATURE
1. With the scan tool, read the Exhaust Temperature Sensors to determine the exhaust temperature.

Is the temperature reading above 225°F?

Yes

- Go To 5

No

- Go To 6

5. EXHAUST TEMPERATURE SENSORS
1. Start the engine.
2. Raise the engine speed to 2500 RPM's for two minutes.

Does the temperature readings of all three Exhaust Temperature Sensors change in value at least 5°F?

Yes

- Go To 7

No

- Replace the Exhaust Temperature Sensor that did not change in value by at least 5°F or is not updating.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

6. EXHAUST TEMPERATURE SENSORS
1. Start the engine and allow it to idle for 10 minutes.
2. With the scan tool, read the values of all three Exhaust Temperature Sensors.

Do all three temperature sensors read above 150°F and are the values of the temperature sensors updating?

Yes

- Go To 7

No

- Replace the Exhaust Temperature Sensor that is not above 150°F or is not updating on the scan tool.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

7. CHECK THE CHARGE AIR COOLING SYSTEM FOR CONTAMINATION DAMAGING THE AFTERTREATMENT DIESEL OXIDATION CATALYST
1. Separate the exhaust plumbing from the Turbocharger outlet.
2. Inspect for signs of oil, coolant or fuel being introduced into the after treatment system from the engine or signs of moisture in the Turbocharger exhaust outlet.

Is contamination found in the turbocharger exhaust outlet?

Yes

- Identify and repair the source of the contamination within the engine and replace the After treatment Diesel Oxidation Catalyst after the engine failure has been repaired.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 8

8. AFTERTREATMENT DIESEL OXIDATION CATALYST INLET AND/OR OUTLET TEMPERATURE SENSORS
1. Remove the After treatment Diesel Oxidation Catalyst and temperature sensors and inspect for damage and presence of face plugging.

Are the components found to be missing, plugged or damaged during the inspection of the After treatment Diesel Oxidation Catalyst and temperature sensors?

Yes

- Replace or repair damaged component(s).
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 9

9. AFTERTREATMENT DIESEL PARTICULATE FILTER
1. Remove the exhaust pipe and inspect the After treatment Diesel Particulate Filter.

Does After treatment Diesel Particulate Filter show evidence of failure?

Yes

- Replace the After treatment Diesel Particulate Filter, clean the EGR Valve, and reset the regenerative timers with the scan tool.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test