P0420

P0420-CATALYST EFFICIENCY (BANK 1)

Special Tools:

For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

The State of Change (SOC) catalyst monitor uses the signals from both the upstream and downstream O2 sensors to detect aging of the catalyst. Based on the fact that when a catalyst ages, it loses some of its Oxygen Storage Capacity (OSC). As a result, part of the untreated exhaust gases can breakthrough the catalyst and causes the downstream O2 sensor to deviate from its neutral (Stoichiometric) position. By observing the activities in the downstream O2 signal, the degradation level of catalyst can be detected. In general, the higher the downstream O2 sensor SOC value, the more exhaust gas breakthrough and the lower the OSC of the catalytic converter.

- When Monitored:
Engine Coolant Temperature (ECT) above 70° C (158° F), engine RPM between 1400 and 2300, vehicle speed between 64 and 96 kph (40 and 60 mph) and engine run time greater than three minutes.

- Set Condition:
If the final State of Change index is within the calibrated fail threshold. Two trip fault. 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 DTCs 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. Start the engine.
2. Allow the engine to reach normal operating temperature.
3. With the scan tool, select View DTCs.

NOTE: It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.

Is the DTC Active or Pending at this time?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition 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. (K902) O2 RETURN UPSTREAM CIRCUIT VOLTAGE CHECK

1. Turn the ignition off.
2. Disconnect the 1/1 O2 Sensor harness connector.
3. Turn the ignition on.
4. Measure the voltage on the (K902) O2 Return Upstream circuit in the O2 Sensor harness connector.

Is the voltage at 2.5 Volts?

Yes

- Go To 4

No

- Go To 5

4. (K904) O2 RETURN DOWNSTREAM CIRCUIT VOLTAGE CHECK

1. Turn the ignition off.
2. Disconnect the 1/2 O2 Sensor harness connector.
3. Turn the ignition on.
4. Measure the voltage on the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.

Is the voltage at 2.5 Volts?

Yes

- Go To 10

No

- Go To 7

5. (K902) O2 RETURN UPSTREAM CIRCUIT SHORTED TO GROUND

1. Turn the ignition off.
2. Disconnect the C1 and C2 PCM harness connectors.
3. Measure the resistance between ground and the (K902) O2 Return Upstream circuit in the 1/1 O2 Sensor harness connector.

Is the resistance below 100 Ohms?

Yes

- Repair the short to ground in the (K902) O2 Return Upstream circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 6

6. (K902) O2 RETURN UPSTREAM CIRCUIT OPEN

1. Turn the ignition off.
2. Disconnect the 1/2 O2 harness connector.
3. Measure the resistance between ground and the (K904) O2 Return Downstream circuit in the 1/2 O2 Sensor harness connector.

Is the resistance below 100 Ohms?

Yes

- Repair the short to ground in the (K904) O2 Return Downstream circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 8

8. (K904) O2 RETURN DOWNSTREAM CIRCUIT OPEN

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install the PCM Pinout Box (8815A) to perform diagnosis.

1. Measure the resistance of the (K904) O2 Return Downstream circuit from the 1/2 O2 Sensor harness connector to the appropriate terminal of PCM Pinout Box.

Is the resistance below 5.0 Ohms?

Yes

- Go To 9

No

- Repair the open in the (K904) O2 Return Downstream circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

9. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Sensor and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the Sensor and the Powertrain Control Module connectors.
4. Perform any Technical Service Bulletins that may apply.

Were there any problems found?

Yes

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

No

- Replace and program the Powertrain Control Module.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

10. CHECKING THE EXHAUST SYSTEM FOR LEAKS
1. Turn the ignition off.
2. Raise the vehicle.

WARNING: The normal operating temperature of the exhaust system is very high. Never work around or attempt to service any part of the exhaust system until it has cooled. Special care should be taken when working near the catalytic converter. The temperature of the converter rises to a high level after a short period of engine operating time.

3. Connect Exhaust Cone or to Air Pressure Regulator (with hose) W-18-MIL-1146AS.

CAUTION: The air pressure must not exceed 27.6 kPa (4 psi), otherwise engine damage can occur.

4. Attach shop air to the air pressure regulator.
5. Adjust the Air Pressure Regulator to 27.6 kPa (4 psi).
6. Insert the exhaust cone into the vehicle tail pipe.
7. If the vehicle is equipped with dual exhaust. Use the with equipped attached plug, plug one side of the dual exhaust pipe. Pressurize the other as described above.
8. Apply Mopar(R) Air Leak Detector PN# 05191804AA (or an equivalent leak finder liquid) to the following areas:
- All welded joints from the exhaust manifold to 152.4 mm (6 inches) behind the downstream O2 sensor
- O2 sensor seal points
- O2 sensor boss welds
- Flange/joint connection(s)
- Exhaust manifold to cylinder head connection(s)
- EGR solenoid gasket base and tube seal points (if equipped)

9. Watch for the liquid/soapy water to bubble.
10. Use the following definitions to help determine if system or component repair/replacement is necessary:
Type 1 Leak is defined as a leak where very small foam like bubbles 1 mm (0.04 of an inch) or less appear.

Any Type 1 or greater leaks found in welded joints, O2 sensor seal points or O2 sensor boss welds must be repaired or the component must be replaced.

Type 2 Leak is defined as a leak where larger bubbles pea size, 8 mm (0.3 of an inch) or greater appear.

Any Type 2 or greater leaks found in flange or joint connections, exhaust manifold to cylinder head connections or EGR gasket and tube seal points must be repaired or the components must be replaced.

11. If a leak is found that matches the above definition, repair or replace the component as necessary.
12. Once the repair is complete, repeat the procedure to verify that all leaks have been repaired.

Were any exhaust leaks found?

Yes

- Repair or replace the leaking exhaust parts as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 11

11. 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 12

12. 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 13

13. CATALYTIC CONVERTER

If there are no possible cause remaining, view repair.

Repair

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