Circuit Description
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the post-catalyst HO2S. This HO2S produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalysts ability to convert exhaust gases efficiently. If the post HO2S signal voltage remains excessively low for an extended period of time, this DTC will set.
Conditions for Running the DTC
| • | No Misfire, Transmission, Fuel injector, MAF, TP, EVAP, IAT, MAP, Fuel trim, EGR or ECT DTCs are present. |
| • | Closed loop commanded air/fuel ratio is between 14.5 - 14.8. |
| • | Throttle angle is between 5 percent and 40 percent. |
| • | The engine coolant temperature is more than 75°C (165°F). |
Conditions for Setting the DTC
Post HO2S signal voltage remains less than 60 mV during normal closed loop operation.
OR
Post HO2S signal voltage remains less than 600 mV during power enrichment mode.
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect for the following:
| • | Fuel pressure low - A condition which causes a lean exhaust can cause this DTC to set. The system will go lean if pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure is too low, this DTC may set. Refer to Fuel System Pressure Test . |
| • | Fuel injectors faulty - Refer to Fuel Injector Balance Test . |
| • | Vacuum leaks - Inspect for a disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, throttle body, EGR system, and crankcase ventilation system. |
| • | Exhaust leaks - An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing this DTC to set. Inspect for exhaust leaks near the oxygen sensors. |
| • | MAF sensor faulty - Disconnect the MAF sensor and see if the condition is corrected. If so, replace MAF sensor. |
| • | Fuel contamination - Water, even in small amounts, can be delivered to the fuel injectors. The water can cause a lean exhaust to be indicated. Excessive alcohol in the fuel can also cause this condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
This DTC setting during power enrichment mode conditions may indicate a condition described in the Diagnostic Aids above. If this DTC test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.
-
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Important: During this step, observe the pre-catalyst HO2S voltage parameters. If the pre-catalyst parameters remain below 400mV, refer to Diagnostic Aids.
Does the HO2S voltage remain less than the specified value? | 75 mV | ||
Operate vehicle within Fail Records conditions. Does the scan tool indicate this DTC failed this ignition? | -- | Go to Diagnostic Aids | ||
4 | Disconnect HO2S and jumper the low circuit (PCM side) to a good ground. Does scan tool indicate HO2S voltage near the specified value? | 450 mV | Go to Diagnostic Aids | |
5 | Test the HO2S signal circuit for a short to ground or a short to the sensor ground circuit. Refer to Circuit Testing in Wiring Systems. Did you find a problem? | -- | ||
6 | Repair the HO2S signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
|
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||
8 |
Does the DTC reset? | -- | System OK |
