Circuit Description
The engine controls systems uses a three-way catalytic converter (TWC) to control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). The catalyst within the TWC promotes a chemical reaction, which oxidizes the HC and CO that are present in the exhaust gas. This reaction converts these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces the NOx which converts into nitrogen. The powertrain control module (PCM) monitors this process using heated oxygen sensors (HO2S) bank 1 sensor 2 and HO2S bank 2 sensor 2, which are located in the exhaust stream past the TWC. These sensors are referred to as catalyst monitor sensors (CatMon). The catalyst monitor sensors produce an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to effectively convert the exhaust emissions. If the catalyst is functioning correctly, the catalyst monitor signals will be far less active than that of the signals which are produced by the fuel control HO2S 1 bank 1 and fuel control HO2S 1 bank 2. This indicates that the TWC oxygen storage capacity is at an acceptable threshold. When the response time of the catalyst monitors are close to that of the fuel control sensors, the ability of the catalyst to store oxygen is considered to be below an acceptable threshold. If the PCM detects this condition, DTC P0420 catalyst low efficiency for bank 1 or DTC P0430 catalyst low efficiency for bank 2 sets.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0125, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0171, P0172, P0174, P0175, P0200, P0220, P0300, P0325, P0327, P0332, P0335, P0336, P0341, P0342, P0343, P0351-P0358, P0442, P0443, P0446, P0452, P0453, P0455, P0496, P0502, P0503, P1125, P1133, P1153, P1514, P1516, P1518, P2108, P2135 are not set. |
| • | The intake air temperature (IAT) is between -7°C and +85°C (+19°F and +185°F). |
| • | The barometric pressure (BARO) is more than 74 kPa. |
| • | The vehicle has been driven at more than 900 RPM for 50 seconds. |
| • | The engine coolant temperature (ECT) is more than 70-120°C (158-248°F). |
| • | The engine must be at idle for the one of the following amounts of time: |
| - | 45 seconds in neutral for manual transmissions |
| - | 40 seconds in gear for automatic transmissions |
| • | The Closed Loop fuel control is enabled. |
Conditions for Setting the DTC
The PCM determines that the oxygen storage capability of the TWC has degraded to less than a calibrated threshold.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | The catalyst test may abort due to a change in the engine load. DO NOT change the engine load during the test. During the test, DO NOT touch the following: |
| - | The AC |
| - | The steering wheel |
| - | the heater motor |
| • | Ensure that the coolant fan is not cycling while a catalyst test is in progress. |
| • | Inspect the fuel control oxygen sensor wiring harness for a short to the catalysts monitor wiring harness. |
| • | Driving the vehicle under the conditions outlined in the inspection/maintenance (I/M) section can verify whether the fault is present. |
| • | Certain conditions may cause a catalytic converter to degrade. These conditions may include the following: |
| - | An engine misfire, which can cause catalytic convertor overheating |
| - | High engine oil or high coolant consumption |
| - | Retarded spark timing |
| - | A condition that may cause low secondary ignition voltage, which can cause incomplete combustion |
| - | A lean fuel mixture |
| - | A rich fuel mixture |
| - | A shorted 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 the Freeze Frame/Failure Records can be useful in determining the vehicle operating conditions when the DTC was set. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step inspects for conditions that can cause the three-way catalytic converter efficiency to appear degraded.
-
A catalytic converter which has been discolored may be due to an engine running rich, lean or had a previous severe misfire. Verifying the fuel trim percentages may be of assistance in determining if such a condition exists.
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |||||||||
2 | Review the DTC information on the scan tool. Are any component DTCs set? | Go to Step 3 | |||||||||
3 |
Is the HO2S 2 voltage parameter as active as the HO2S 1 voltage parameter for the applicable bank? | Go to Step 5 | Go to Step 4 | ||||||||
4 |
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 original equipment manufacture (OEM) specifications. Visually and physically inspect the three-way catalytic convertor for the following conditions:
Did you find and correct the condition? | Go to Step 7 | Go to Step 6 | ||||||||
Visually inspect the exhaust system for the following conditions:
Did you find and correct the condition? | Go to Step 9 | Go to Step 7 | |||||||||
7 | Visually inspect the catalyst monitor HO2S 2 for the following conditions:
Did you find and correct the condition? | Go to Step 9 | Go to Step 8 | ||||||||
|
Important: Locate and repair the cause of the three-way catalytic converter failure before installing the replacement convertor. Replace the three-way catalytic converter. Refer to Catalytic Converter Replacement in Engine Exhaust. Did you complete the replacement? | Go to Step 9 | -- | |||||||||
9 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 10 | ||||||||
10 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK |
