Diagnostic Aids

WARNING: This page is about a different variant/trim than selected.

The catalyst may have been temporarily contaminated with a chemical from an aftermarket fuel additive or fuel containing too much sulfur. The sulfur will coat the converter wash coat causing the converter performance to degrade temporarily. Driving the vehicle at highway speeds for 10 minutes will burn off the contamination. Retest the converter afterwards.
Certain conditions may cause a catalytic converter to degrade. These conditions may include the following:
- An engine misfire
- High engine oil or high coolant consumption
- Retarded spark timing
- A weak spark
- A lean fuel mixture
- A rich fuel mixture
- A damaged oxygen sensor wiring harness
Correct any condition that may cause an engine performance concern.
If an intermittent condition cannot be duplicated, the information included in Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was set.

DTC P0420 or P0430

Step	Action	Values	Yes	No
1	Did you perform the Diagnostic System Check - Vehicle?	-	Go to Step 2	Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2	Review the DTC information on the scan tool. Are any other DTCs set?	-	Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	Go to Step 3
3	Allow the engine to reach operating temperature. Ensure Closed Loop is achieved. Increase the engine speed to 2,000 RPM for 2 minutes. Return the engine to a stabilized idle. Observe the catalyst monitor HO2S 2 voltage parameter on the scan tool for the applicable bank. Is the HO2S 2 parameter transitioning below the first specified value and above the second specified value?	300 mV 650 mV	Go to Step 5	Go to Step 4
4	CAUTION: Refer to Road Test Caution in Cautions and Notices. Clear the DTCs with a scan tool. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did DTC P0420 or P0430 set?	-	Go to Step 5	Go to Diagnostic Aids
5	IMPORTANT: Verify that the three-way catalytic converter is a high quality part that meets the OEM specifications. Visually and physically inspect the three-way catalytic convertor for the following conditions: Any dents A severe discoloration caused by excessive temperatures Any internal rattles caused by loose catalyst substrate Did you find and correct the condition?	-	Go to Step 10	Go to Step 6
6	Visually inspect the exhaust system for the following conditions: The exhaust system for leaks-Refer to Exhaust Leakage in Engine Exhaust. The exhaust system for a restriction-Refer to Restricted Exhaust in Engine Exhaust. Any physical damage Any loose or missing hardware The heated oxygen sensor (HO2S) 2 for the applicable bank for proper torque Did you find and correct the condition?	-	Go to Step 10	Go to Step 7
7	Visually inspect the HO2S 2 at the applicable bank for the following conditions: The pigtail and the wiring harness making contact with the exhaust or any ground Any dents Did you find a condition?	-	Go to Step 8	Go to Step 9
8	Replace the applicable HO2S 2 sensor. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 . Did you complete the replacement?	-	Go to Step 10	-
9	NOTE: In order to avoid damaging the replacement three-way catalytic converter, correct the engine misfire or mechanical fault before replacing the three-way catalytic converter. Replace the three-way catalytic converter.Did you complete the replacement?	-	Go to Step 10	-
10	CAUTION: Refer to Road Test Caution in Cautions and Notices. IMPORTANT: A new catalyst may fail this test due to out-gassing of the internal matting. If this occurs, operate the vehicle at highway speeds for approximately one hour and retest. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition?	-	Go to Step 2	Go to Step 11
11	Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed?	-	Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	System OK