For 1990-2009 cars

### 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 Descriptors

DTC P0420: Catalyst System Low Efficiency Bank 1
DTC P0430: Catalyst System Low Efficiency Bank 2

### Circuit/System Description

Note: A new converter with less than 100 miles on it may set P0420 or P0430 due to out-bubbles of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

A 3-way catalytic converter (TWC) controls emissions by converting hydrocarbons (HC) and carbon monoxide (CO) into carbon dioxide (CO2), and oxides of nitrogen (NOx) into nitrogen. The 3-way catalytic converter also stores oxygen. When the listed idle conditions follow the listed driving conditions, the Catalyst System Efficiency test will run. The engine control module (ECM) monitors this oxygen storage capacity by comparing the pre and post-catalyst oxygen sensor signals while adding and subtracting fuel during specific idle conditions. The ECM compares the pre-catalyst and post-catalyst oxygen sensor signals to determine if the oxygen storage capacity of the catalyst is degraded.

### Conditions for Running the DTC

1. Driving Condition

DTCs P0010, P0011, P0013, P0014, P0016, P0017, P0018, P0019, P0030, P0036, P0053, P0054, P0059, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0151- P0155, P0171, P0172, P0174, P0175, P0201-P0208, P0220, P0222, P0223, P0315, P0300, P0301-P0308, P0335, P0336, P0340, P0341, P0345, P0346, P0351-P0358, P0401, P0403, P0404, P0405, P0406, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P0506, P0507, P060D, P1101, P1133, P1153, P1174, P1175, P1258, P1400, P1404, P1516, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, P2176,P2A00, P2A01, P2A03 or U0107 are not set.

2. Idle Condition

• | The Throttle Position (TP) is less than 2.0 percent

• | The vehicle speed is less than the specified value.

• | The vehicle is driven at more than 1,000 RPM for more than 20 seconds since the last idling.

• | The engine run time is greater than specified time.

• | This diagnostic attempts one test during each valid idle period when the above conditions have been met. This test attempts up to 17 times during each drive cycle.

• | The diagnoses for three way catalyst on the current cycle has not finished.

3. While the vehicle meets the two conditions listed above, the normal running for the three-way catalyst under idle conditions should meet the following conditions;

• | The intake air temperature (IAT) is between -20 to +250° C (-4 to 482° F).

• | Other tests are not set

• | The battery voltage is above 11 volts.

• | Without the evaluation of alcohol content

• | The Engine Coolant Temperature (ECT) is within the allowable range.

• | The Barometric Pressure (BARO) is greater than 70 kPa

• | The idle time is less than the specified time before the intrusive test, and the idle time will increase when the speed and the throttle position (TP) angle reduce.

• | The short term fuel trim (FT) is between -10 and 10 percent;

• | The expected three-way catalytic temperature exceeds the specified value or the air flow of the engine is more than 12 g/s for at least 30 seconds with the throttle closed for 180 seconds.

| OR

• | Fuel is in Closed Loop

• | The current gear is Forward

4. After the vehicle speed is stable at idle, the normal running for three-way catalyst should meet the following conditions:

• | The mass air flow (MAF) is between 3-18 g/s;

• | The expected catalytic temperature is less than 640° C (1184° F)

5. Three Way Catalytic Converter runs for 8 seconds while the conditions are met, check whether the following conditions related to engine fuel meet the requirements:

• | The pre-conversion times of oxygen sensor is at least once;

• | The Short Term FT Avg is between -4 and +4 percent;

### Conditions for Setting the DTC

• | The ECM has determined that the catalyst efficiency has degraded below a calibrated threshold.

• | This diagnostic may conclude as one test attempt. However, this diagnostic may require as many as 18 test attempts, which would require at least 3 drive cycles.

### Action Taken When the DTC Sets

DTCs P0420 and P0430 are Type A DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0420 and P0430 are Type A DTCs.

### Reference Information

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Engine Control Module Scan Tool Information

### Circuit/System Verification

Caution: Refer to Heated Oxygen Sensor Resistance Learn Reset Caution in the Preface section.

Caution: Refer to Three-Way Catalytic Converter Damage Caution in the Preface section.

Note: A new converter with less than 100 miles on it may set DTC P0420 or P0430 due to out-bubbles of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

1. If any other DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
2. Inspect for the following conditions, which may cause a catalytic converter to degrade:

• | An engine misfire

• | High engine oil or high coolant consumption

• | Retarded spark timing

• | A weak or poor spark

• | A lean fuel mixture

• | A rich fuel mixture

• | A damaged oxygen sensor or wiring harness

• | The catalyst test may abort if the vehicle falls outside the conditions for running the DTC.

• | A catalyst may be temporarily degraded if a fuel with high sulfur content has been used. Drive the vehicle at highway speeds for 10 minutes and retest the converter.

3. Operate the vehicle within the Conditions for Running the DTC.

⇒ | If the DTC fails this key cycle, continue with this procedure.

4. Inspect the catalytic converter for the following conditions:

• | Any dents

• | A severe discoloration caused by excessive temperatures

• | Road damage

• | An internal rattle caused by damaged catalyst substrate

• | Restrictions

⇒ | If a condition is found, replace the catalytic converter.

5. Inspect the exhaust system for the following conditions:

• | Leaking

• | Physical damage

• | Loose or missing hardware

• | Properly torqued HO2S

• | Restrictions

⇒ | If a condition is found, repair the exhaust system.

6. Inspect the rear catalytic HO2S for the following conditions:

• | Harness Short to Ground

• | Damage

⇒ | If a condition is found, replace the post catalytic HO2S.

⇒ | If no physical condition is detected, replace the catalytic converter.

### Repair Instructions

Note: A new converter with less than 100 miles on it may set DTC P0420 or P0430 due to out-bubbles of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

• | Catalytic Converter Replacement - Left Side

• | Catalytic Converter Replacement - Right Side

• | Restricted Exhaust

### Repair Verification

1. Clear all DTCs.
2. Engine Coolant Temperature reaches to 70°C (156°F).

• | Put the shift lever in Park, Neutral.

• | Apply the parking brake.

3. Apply and hold brake pedal.
4. Run the engine for 6 minutes at 2,500 RPM.
5. Allow engine speed to return to idle speed, then place shift lever into Forward, or press the clutch pedal for the manual transmission.
6. After 2 minutes, verify that DTC P0420 or P0430 have passed or failed this ignition cycle.

⇒ | The above test may need to be repeated up to 5 times during this drive cycle. The first test should be run after the initial warm up period of 6 minutes. During the subsequent tests, maintain 2,500 RPM for 2 minutes.

7. If 6 tests have been attempted and the DTC has not run or passed during this key cycle, turn the ignition OFF for 30 seconds, then run the procedure a second time.