Description
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. if the PCM detects a level of catalyst monitor HO2S activity that indicates the catalyst is no longer operating effectively, this DTC will set.
DTC Descriptors
This diagnostic procedure supports the following DTCs.
| • | DTC P0420 Catalyst System Low Efficiency Bank 1 |
| • | DTC P0430 Catalyst System Low Efficiency Bank 2 |
Condition for Running the DTC
| • | Before the PCM can report DTC P0420 or DTC P0430 failed, DTC P0442 must run and pass. |
| • | DTCs P0030, P0036, P0050, P0056, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0133, P0135, P0137, P0138, P0139, P0141, P0153, P0155, P0157, P0158, P0159, P0161, P0171, P0172, P0174, P0175, P0201-P0206, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0335, P0336, P0341, P0401, P0403, P0404, P0443, P0496, P0501, P0641, P0651, P0720, P1128, P1129, P2227, P2228, P2229, P2297, P2298, P2413, P2414, P2415, or P2646 are not set. |
| • | The engine coolant temperature is more than 69°C (156° F). |
| • | The intake air temperature is more than -21°C ( 6° F). |
| • | The estimated TWC temperature is more than 500° C (932°F). |
| • | The engine speed is between 1,150 RPM and 2,000 RPM. |
| • | The manifold absolute pressure (MAP) is between 22 kPa and 74 kPa. |
| • | The vehicle speed is 7 km/h (4 mph) or more. |
| • | The engine is in closed loop. |
| • | DTC P0420 and DTC P0430 run once per drive cycle when the above conditions are met. |
Conditions for Setting the DTC
The PCM determined the catalyst efficiency has degraded below a calibrated threshold.
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
| • | Inspect for the following conditions: |
| - | An exhaust leak can affect the HO2S accuracy. |
| - | Inspect for a damaged front or rear oxygen sensor wiring harness. |
| • | A TWC converter failure may be caused by any of the following conditions: |
| - | Engine misfire can cause catalytic converter overheating. |
| - | Inadequate secondary ignition voltage can cause incomplete combustion and catalytic converter overheating. |
| - | Retarded ignition timing can cause performance concerns. |
| - | Excessive engine oil or engine coolant consumption can damage the catalytic converter. |
| - | Rich engine fueling can cause catalytic converter overheating. |
| • | 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. |
| • | 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.
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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.
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This step verifies whether the malfunction is presently occurring.
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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.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||||
2 | Check any for any heated oxygen sensor DTCs and diagnose those DTCs first. Are there any heated oxygen sensor DTCs set? | -- | Go to Step 3 | |||||||||
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 |
Did DTC P0420 or DTC P0430 set? | -- | Go to Step 5 | Go to Diagnostic Aids | ||||||||
5 |
Did you find a problem? | -- | Go to Step 8 | Go to Step 6 | ||||||||
6 |
Was a repair necessary? | -- | Go to Step 9 | Go to Step 7 | ||||||||
7 |
Was a repair necessary? | -- | Go to Step 9 | Go to Step 8 | ||||||||
|
Important: Locate and repair the cause of the TWC converter failure before installing the replacement converter. Replace the 3-way catalytic converter. Is the action complete? | -- | Go to Step 10 | -- | |||||||||
9 |
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 |
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? | -- | System OK |
