For 1990-2009 cars

### Description

The DTC P0420 Catalyst System Low Efficiency Bank 1 diagnostic monitors the operation the bank 1 warm-up catalytic converter. The DTC P0430 Catalyst System Low Efficiency Bank 2 diagnostic checks the operation of the bank 2 warm-up catalytic converter. In order to control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), a three-way catalytic (TWC) converter is used. The catalyst within the converter promotes a chemical reaction that oxidizes the HC and the CO that is present in the exhaust gases. The oxidation process converts the HC and CO into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting NOx to nitrogen. The powertrain control module (PCM) has the ability to monitor this process using the fuel control heated oxygen sensors (HO2S) and catalyst monitoring HO2S. The fuel control HO2S produces an output signal which indicates the amount of oxygen present in the exhaust gases entering the TWC converter. The catalyst monitor HO2S produces an output signal that indicates the oxygen storage capacity of the catalyst in the TWC converter. The oxygen storage capacity of the catalyst is an indicator of the converter ability to convert exhaust gases efficiently. The fuel control HO2S output signal will be far more active than the catalyst monitor HO2S output signal when the converter catalyst is operating efficiently. A DTC P0420 or DTC P0430 will set if the PCM detects a level of catalyst monitor HO2S activity that indicates the catalyst is no longer operating effectively.

### Condition for Running the DTC

• | The barometric pressure (BARO) is more than 75 kPa.

• | The engine coolant temperature is between -8°C and +110°C (18°F-230°F).

• | The intake air temperature is more than -8°C (+18°F).

• | The engine is operating in Closed Loop.

### Conditions for Setting the DTC

• | The high and low voltage swing of the catalyst monitor HO2S is similar to the high and low voltage swing of the fuel control HO2S.

• | The above conditions are present for 96 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

### Conditions for Clearing the MIL/DTC

• | The MIL turns OFF after 3 consecutively passing trips without a fault present.

• | A history DTC clears after 40 consecutive warm-up cycles without a fault.

• | Perform the scan tool Clear DTC Information function in order to clear the DTC.

### Diagnostic Aids

Check for any of the following conditions:

• | Exhaust gas leaks can affect the accuracy HO2S. Refer to Exhaust Leakage in Engine Exhaust.

• | A damaged oxygen sensor wiring harness--Inspect the HO2S 1 and HO2S 2 wiring harnesses for damage and repair as necessary.

A TWC converter failure may be caused by any of the following conditions:

• | Engine misfire can cause catalytic converter overheating. Refer to Symptoms - Engine Controls .

• | Inadequate secondary ignition voltage can cause incomplete combustion and catalytic converter overheating. Refer to Electronic Ignition (EI) System Diagnosis .

• | Retarded ignition timing can cause performance concerns. Refer to Ignition System Timing Adjustment .

| Excessive engine oil or engine coolant consumption can damage the catalytic converter. Refer to Base Engine Misfire with Excessive Oil Consumption or Base Engine Misfire with Coolant Consumption in Engine Mechanical-2.5L (LE8).

• | Rich engine fueling can cause catalytic converter overheating. Refer to DTC P0172 or DTC P0175 .

If a DTC P0420 or a DTC P0430 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance (I/M) Catalyst System Set Procedure .

If a DTC P0420 or DTC P0430 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and to store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step verifies whether the malfunction is presently occurring.

3. This step checks whether the malfunction that caused the DTC P0420 or P0430 is still present. Driving the vehicle under these conditions will verify whether the fault is present. After performing the scan tool Clear DTC Information function, the DTC P0420 or P0430 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If DTC P0420 or P0430 appears in the Not Ran Since Code Cleared list, the P0420 or P0430 diagnostic has not yet run. When DTC P0420 or P0430 does not appear in the Not Ran Since Code Cleared list, the P0420 or P0430 diagnostic has run. If the MIL is NOT illuminated and there is no Pending DTC Status in DTC Information, the P0420 or P0430 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.

4. In order to avoid repeated replacement of the catalytic converter, inspect for the cause of the converter failure and repair as necessary. Refer to Diagnostic Aids.

5. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0420 or P0430 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0420 or P0430 appears in the Not Ran Since Code Cleared list, the DTC P0420 or P0430 diagnostic has not yet run. When the DTC P0420 or P0430 does not appear in the Not Ran Since Code Cleared list, the DTC P0420 or P0430 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0420 or P0430 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.

Step |  | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Check any for any heated oxygen sensor DTCs and diagnose those DTCs first. Are there any heated oxygen sensor DTCs set? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Step 3
3 |

1. Install a scan tool.
2. Start the engine.
3. Run the engine until the normal operating temperature is reached.
4. Verify that the engine is operating in Closed Loop.
5. Run the engine at the specified value for 3 minutes.
6. Monitor the fuel control HO2S and the catalyst monitor HO2S signals of the suspect converter on the scan tool.

Is the catalyst monitoring HO2S signal as active as the fuel control HO2S signal?

2,500-3,000 RPM

Go to Step 5

Go to Step 4

4 |

1. Perform the scan tool Clear DTC Information function.
2. Operate the vehicle within the Freeze Frame conditions as specified or until the P0420/P0430 diagnostic test has run. Refer to the Test Description.

Did DTC P0420 or DTC P0430 set?

--

Go to Step 5

Go to Diagnostic Aids

5 |

1. Visually and physically inspect the suspect 3-way catalytic converter for the following concerns:

• | Dents or physical damage

• | Severe discoloration caused by excessive temperatures

• | Holes or punctures

• | Internal rattles caused by a damaged catalyst element

2. Verify that the 3-way catalytic converter is a high quality part that meets the OEM specifications.

Did you find a problem?

--

Go to Step 8

Go to Step 6

6 |

1. Visually and physically inspect the exhaust system for any of the following conditions:

• | Leaks

• | Refer to Exhaust Leakage in Engine Exhaust.

• | Physical damage

• | Loose or missing hardware

2. Repair as necessary.

Was a repair necessary?

--

Go to Step 9

Go to Step 7

7 |

1. Visually and physically inspect the catalyst monitor HO2S of the suspect converter for the following conditions:

• | The pigtail and wiring harness making contact with exhaust pipe

• | A loose HO2S

• | Any road damage

2. Repair as necessary.

Was a repair necessary?

--

Go to Step 9

Go to Step 8

8 | Important: Locate and repair the cause of the TWC converter failure before installing the replacement converter. Replace the right side or the left side 3-way catalytic converter as necessary. Refer to Exhaust Manifold Replacement in Engine Exhaust.

Is the action complete?

--

Go to Step 10

--

9 |

1. Start the engine.
2. Run the engine until the normal operating temperature is reached.
3. Verify that the engine is operating in Closed Loop.
4. Run the engine at the specified value for 3 minutes.
5. Monitor the fuel control HO2S and the catalyst monitor HO2S signals of the suspect converter on the scan tool.

Is the catalyst monitoring HO2S signal as active as the fuel control HO2S signal?

2,500-3,000 RPM

Go to Diagnostic Aids

Go to Step 10

10 |

1. Turn OFF the ignition.
2. Remove the DOME fuse for 30 seconds.
3. Install the DOME fuse.
4. Reset the radio clock time. Refer to Radio/Audio System Description and Operation in Entertainment.
5. Start the engine.
6. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or until the DTC P0420 or P0430 diagnostic test has run.

Does the DTC run and pass?

--

Go to Step 11

Go to Step 2

11 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK