Circuit Description
A three-way catalytic converter (TWC) controls emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO that are present in the exhaust gas. This process converts these chemicals into water vapor and carbon dioxide (CO2), and will reduce the NOx, converting the NOx into nitrogen.
The catalytic converter stores oxygen. The efficiency of the TWC is determined by the measurement of the oxygen storage capacity (OSC). The engine control module (ECM) measures the catalyst OSC by monitoring the heated oxygen sensor (HO2S) bank 1 sensor 2 and HO2S bank 2 sensor 2, during a steady state cruise. The ECM commands the air-to-fuel ratio lean and then rich for a calibrated number of cycles while monitoring the response time of the HO2S 2. The ECM then establishes an average response time from subsequent air-to-fuel ratio cycles. The difference of the average response time determines the OSC of the catalyst. If the ECM detects low TWC efficiency DTC P0420 for bank 1 or DTC P0430 for bank 2 sets.
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 |
Conditions for Running the DTC
| • | DTCs P0030-P0032, P0031, P0036, P0037, P0038, P0050-P0052, P0051, P0056-P0058, P0057, P0101, P0102, P0103, P0121, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0138, P0140, P0137-P0141, P0150-P0158, P0160, P0161, P0171, P0172, P0174, P0175, P0221, P0222, P0223, P0300-P0306, P0313, P0335, P0336, P0340, P0341, P0440, P0442-P0449, P0451, P0452, P0453, P0455, P0458, P0459, P0496, or P0500 are not set. |
| • | The engine has been running for more than 10 minutes. |
| • | The engine speed is between 1,200-3,000 RPM. |
| • | The calculated catalyst temperature is between 520-720°C (968-1,454°F). |
| • | The engine is in Closed Loop fuel control. |
| • | The vehicle speed sensor (VSS) is between 20-100 km/h (13-62 mph). |
| • | The engine is at a steady cruise, with no load variation. |
| • | The engine load is between 25-45 percent. |
| • | Before the ECM can report DTC P0420 or P0430 failed, the HO2S response test and HO2S heater response test have run and passed. |
| • | A drive cycle is completed once the above conditions are met. |
| • | DTCs P0420 and P0430 run continuously once the above conditions are met. |
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) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the 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
| • | Fuel with a high sulfur content can cause inaccurate converter test results. Verify the fuel quality. |
| • | 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. |
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Vehicle? | -- | Go to Step 2 | |||||||||
2 | Review the DTC information on the scan tool. Are any other DTCs set? | -- | Go to Step 3 | |||||||||
3 |
Is the HO2S 2 parameter transitioning below the first specified value and above the second specified value? | 300 mV 600 mV | 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 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 10 | Go to Step 6 | ||||||||
6 | Visually inspect the exhaust system for the following conditions:
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7 | ||||||||
7 | Visually inspect the heated oxygen sensor (HO2S) 2 at the applicable bank for the following conditions:
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 |
Notice: 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 |
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? | -- | System OK |
