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 provide an overview of each diagnostic category. |
DTC Descriptors
DTC P0131: HO2S Circuit Low Voltage Bank 1 Sensor 1DTC P0151: HO2S Circuit Low Voltage Bank 2 Sensor 1
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
HO2S Bank 1 Sensor 1 Signal | P0131 | P0134, P0135 | P0132 | P0133, P2096, P2097 |
HO2S Bank 1 Sensor 2 Signal | P0137 | P0140 | P0138 | P0140 |
HO2S Bank 2 Sensor 1 Signal | P0151 | P0154, P0155 | P0152 | P0153, P2098, P2099 |
HO2S Bank 2 Sensor 2 Signal | P0157 | P0160 | P0158 | P0160 |
Low Reference | -- | P0134, P0135, P0154, P0155 | -- | -- |
Typical Scan Tool Data
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: Engine operating in Closed Loop Parameter Normal Range: Fluctuates above and below 350-500 mV | |||
Sensor Signal | 0-60 mV | 445-450 mV | 1275 mV |
Low Reference | -- | 445-480 mV | 1275 mV |
Circuit Description
The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of about 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.
The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
Conditions for Running the DTC
| • | DTCs P0116, P0117, P0118, P0119, P0201, P0202, P0203, P0204, P0205, P0206 P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, and P0277 are not set. |
| • | The ignition voltage is greater than 10.5 volts. |
| • | The engine is operating for more than 1 second. |
| • | The engine coolant temperature (ECT) during the previous ignition cycle was more than 60°C (140°F). |
| • | The ECT at startup is less than 40°C (104°F). |
| • | The HO2S heater is active for more than 5 seconds. |
| • | The calculated exhaust temperature is less than 800°C (1,472°F). |
| • | DTC P0131 and P0151 run continuously once the conditions above exist. |
Conditions for Setting the DTC
| • | The ECM detects that a primary HO2S voltage is less than 60 mV while the corresponding secondary HO2S voltage is greater than 500 mV. |
| • | The ECM detects that a primary HO2S voltage is less than 60 mV after a cold start with the engine coolant temperature (ECT) less than 40°C (104°F). |
| • | Either condition exists for more than 4 seconds, or a cumulative of 50 seconds. |
Action Taken when the DTC Sets
DTCs P0131 and P0151 are Type B DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0131 and P0151 are Type B DTCs.
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Circuit/System Verification
- Engine idling, observe the HO2S voltage parameter. The voltage should fluctuate above and below the range of 350-550 mV.
- If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the appropriate HO2S sensor.
- Ignition ON, verify that the HO2S voltage parameter is between 350-500 mV.
- Install a 3A fused jumper wire between the signal circuit terminal B and ground. Verify the HO2S voltage parameter is less than 60 mV.
- Connect a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the HO2S voltage parameter is less than 60 mV.
- Verify that the following conditions do not exist:
- If all circuits/connections test normal, replace the HO2S sensor.
| ⇒ | If less than the specified value, test the signal circuit for a short to ground. If the circuit/connections test normal, replace the ECM. |
| ⇒ | If greater than the specified value, test the signal circuit for a short to voltage. If the circuit/connections test normal, replace the ECM. |
| ⇒ | If greater than the specified value, test the signal circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM. |
| ⇒ | If greater than the specified value, test the low reference circuit for an open/high resistance or for a short to voltage. If the circuit/connections test normal, replace the ECM. |
| • | Lean fuel injectors--Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 . |
| • | Low fuel system pressure--Refer to Fuel System Diagnosis . |
| • | Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | Exhaust leaks near the HO2S |
| • | Engine vacuum leaks |
| ⇒ | If you find any of the above conditions, repair as necessary. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for engine control module replacement, setup, and programming |
