Chevrolet Trax: DTC P0420

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0420

Catalyst System Low Efficiency

Circuit/System Description

A 3-way catalytic converter controls emissions of hydrocarbons, carbon monoxide (CO) and nitrogen oxide (NOx). The catalyst within the converter promotes a chemical reaction, which oxidizes the hydrocarbons and the CO that are present in the exhaust gas. This process converts the hydrocarbons and the CO into water vapor and carbon dioxide (CO2), and reduces the NOx, converting the NOx into nitrogen. The catalytic converter also stores oxygen. The engine control module (ECM) monitors this process by using a heated oxygen sensor (HO2S) that is in the exhaust stream after the 3-way catalytic converter. The HO2S 2 produces an output signal that the ECM uses to calculate the oxygen storage capacity of the catalyst. This indicates the ability of the catalyst to convert the exhaust emissions efficiently. The ECM monitors the efficiency of the catalyst by allowing the catalyst to heat, then wait for a stabilization period while the engine is idling. The ECM then adds and removes fuel while monitoring the HO2S 2. When the catalyst is functioning properly, the HO2S 2 response to the extra fuel is slow compared to the response of the HO2S 1, which is located before the 3-way catalytic converter. When the HO2S 2 response is near that of the HO2S 1, the oxygen storage capability and efficiency of the catalyst may be degraded below an acceptable threshold.

Conditions for Running the DTC

• DTC P0016, P0017, P0030, P0036, P0053, P0054, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0114, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P013A, P013B, P013E, P013F, P0140, P0141, P015A, P015B, P16F3, P0171, P0172, P0222, P0223, P0300, P0301, P0302, P0303, P0304, P0335, P0336, P0340, P0341, P0365, P0366, P0443, P0502, P0503, P0506, P0507, P0606, P0697, P06A3, P2101, P2122, P2123, P2127, P2128, P2135, P2138, P2270 or P2271 is not set.
• Before the ECM performs the idle test, the vehicle must be driven under the following conditions:

• Engine speed is greater than 1,100 RPM for a minimum of 5 s.
• Vehicle speed is less than 2 km/h (1.24 mph).
• Engine runtime is greater than 120 s.

• Run/crank voltage is greater than 11 V.
• Intake air temperature (IAT) is between -20 to +250ºC (-4 to +482ºF).
• Engine coolant temperature (ECT) is between 40-140ºC (104-284ºF).
• Engine has been idling less than 50 s.
• Short term fuel trim is between -20 to +30.
• Barometric pressure (BARO) is greater than 70 kPa.
• Intake mass air flow (MAF) is between 1.50-7.00 g/s.
• Engine is operating in closed loop.
• Calculated catalyst temperature is between 550-950ºC (1,022-1,742ºF).
• Automatic transmission is in drive range.
• This diagnostic attempts one test during each valid idle period once the above conditions have been met.
• This diagnostic attempts up to 8 tests during each drive cycle.

Conditions for Setting the DTC

The ECM determines that the efficiency of the catalyst has degraded below a calibrated threshold.

Action Taken When the DTC Sets

DTC P0420 is a Type A DTC.

Conditions for Clearing the DTC

DTC P0420 is a Type A DTC.

Diagnostic Aids

Inspect for the conditions listed below, which may cause a catalytic converter to degrade:

• Engine misfire.
• High engine oil or high coolant consumption.
• Retarded spark timing.
• Weak or poor spark.
• Lean fuel mixture.
• Rich fuel mixture.
• Damaged oxygen sensor or wiring harness.

Reference Information

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (LUV) , Powertrain Diagnostic Trouble Code (DTC) Type Definitions (2H0)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Ignition On.
2. Verify there are no other DTCs set.

• If other DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

• If no other DTCs are set

3. Operate the vehicle within the Conditions for Running the DTC.
4. Verify the scan tool Catalyst Monitor Not At Idle Test Conditions Met parameter changes to Yes.

• If Yes is not displayed

Refer to step 3.

• If Yes is displayed

5. When the conditions are safe, stop and idle the vehicle in gear if equipped with automatic transmission or neutral if equipped with manual transmission.
6. Verify the Catalyst Monitor Test Result parameter displays Passed when performing the steps listed below:

1. Apply the service brake.
2. Monitor the scan tool Catalyst Monitor Test State parameter. When the parameter indicates Active, the Catalyst Monitor Test is running.

NOTE: When the test has completed, the Catalyst Monitor Test Counter parameter will increment by one and the Catalyst Monitor Test Result parameter will indicate Passed, Failed or No Result.

3. Continue to monitor the parameter. When the parameter indicates Inactive, the Catalyst Monitor Test has completed.

• If No Result is displayed

Repeat steps 3-6 until the Test Result parameter indicates Passed or Failed

• If Failed is displayed

Refer to Circuit /System Testing

• If Passed is displayed

7. All OK.

Circuit/System Testing

1. Verify the conditions listed below do not exist with the catalytic converter(s):

• Dents
• Severe discoloration caused by excessive temperatures
• Road damage
• Internal rattles caused by damaged catalyst substrate
• Restrictions
• If a condition is found

Replace the catalytic converter.

• If no condition is found

2. Verify the conditions listed below do not exist with the exhaust system:

• Leaks
• Physical damage
• Loose or missing hardware
• If a condition is found

Repair or replace the component as necessary.

• If no condition is found

3. Verify the conditions listed below do not exist with the B52B Heated Oxygen Sensor 2:

• Incorrect torque
• Damage
• If a condition is found

Replace the B52B Heated Oxygen Sensor 2 or repair the condition as necessary.

• If no condition is found

4. Replace the exhaust front pipe and the warm up three-way catalytic converter.

Repair Instructions

NOTE: A new converter with less than 160 km (100 mi) on it may set DTC P0420 due to outgassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 h may correct the condition.

• Exhaust Front Pipe Replacement (LUV) , Exhaust Front Pipe Replacement
• Heated Oxygen Sensor Replacement - Sensor 2
• Perform the HO2S Heater Learn procedure with a scan tool after replacing a heated oxygen sensor.
• Warm Up Three-Way Catalytic Converter Replacement (2H0, LUV)

Repair Verification

1. Install any components that have been removed or replaced during diagnosis.
2. Perform any adjustments, programming or setup procedures that are required when a component is removed or replaced.
3. Clear the DTCs with a scan tool.
4. Turn Off the ignition for 60 s
5. Operate the vehicle within the Conditions for Running the DTC.
6. Verify the scan tool Catalyst Monitor Not At Idle Test Conditions Met parameter changes to Yes.

• If Yes is not displayed

Refer to step 5.

• If Yes is displayed

7. When the conditions are safe, stop and idle the vehicle in gear if equipped with automatic transmission or neutral if equipped with manual transmission.
8. Verify the Catalyst Monitor Test Result parameter displays Passed when performing the steps listed below:

1. Apply the service brake.
2. Monitor the scan tool Catalyst Monitor Test State parameter. When the parameter indicates Active, the Catalyst Monitor Test is running.

NOTE: When the test has completed, the Catalyst Monitor Test Counter parameter will increment by one and the Catalyst Monitor Test Result parameter will indicate Passed, Failed or No Result.

3. Continue to monitor the parameter. When the parameter indicates Inactive, the Catalyst Monitor Test has completed.

• If No Result is displayed

Repeat steps 5-8 until the Test Result parameter indicates Passed or Failed

• If Failed is displayed

Refer to Circuit /System Testing

• If Passed is displayed

9. All OK.

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