For 1990-2009 cars

### 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 provides an overview of each diagnostic category.

### DTC Descriptors

DTC P0134: HO2S Circuit Insufficient Activity Bank 1 Sensor 1
DTC P0154: HO2S Circuit Insufficient Activity 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

#### Bank 1 or 2 HO2S 1

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 DTCs

• | DTC P0201, P0202, P0203, P0204, P0205, P0206, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P2146, P2149, P2152, P2155, P216A, or P216D is not set.

• | The ignition voltage is greater than 10 volts.

• | The engine is operating.

• | The HO2S 1 heater duty cycle is greater than 90 percent for more than 5 seconds.

| OR

• | The HO2S 1 heater duty cycle is greater than 68 percent and the calculated exhaust temperature is warmer than 600°C (1112°F) for more than 30 seconds.

• | DTCs P0134 and P0154 run continuously once the conditions above exist for greater than 10 seconds.

### Conditions for Setting the DTCs

• | An HO2S 1 signal voltage is between 400-520 mV, or 400-550 mV when the calculated exhaust temperature is warmer than 800°C (1,472°F)

• | The calculated internal resistance of an HO2S 1 is greater than 40,000 ohms when the calculated exhaust temperature is warmer than 600°C (1,112°F).

• | A corresponding HO2S 1 and HO2S 2 are greater than 200 mV during a decel fuel cut-off greater 3 seconds.

• | DTC P0134 or P0154 set if any of the conditions above exist

### Action Taken when the DTC Sets

DTCs P0134 and P0154 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0134 and P0154 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Engine idling, observe the appropriate scan tool HO2S voltage parameter. The voltage should fluctuate above and below the range of 350-550 mV.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate HO2S.
2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal C and ground.

⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all the components connected to the ignition circuit and replace as necessary.

3. Ignition OFF, connect a test lamp between the heater control circuit terminal D and B+.
4. Idle the engine, and verify the test lamp illuminates or flashes.

⇒ | If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.

5. Ignition ON, verify that the appropriate scan tool HO2S voltage parameter is between 350-500 mV.

⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit/connections test normal, replace the ECM.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.

6. Connect a 3A fused jumper wire between the signal circuit terminal B and ground. Verify the scan tool HO2S voltage parameter is less than 60 mV.

⇒ | If greater than the specified range, test the signal circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.

7. Connect a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool HO2S voltage parameter is less than 60 mV.

⇒ | If greater than the specified range, 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.

8. Verify that none of the following conditions exist:

• | The HO2S is loose

• | Lean or rich condition.

• | Water intrusion in the HO2S harness connector

• | Low or high fuel system pressure--Refer to Fuel System Diagnosis.

• | Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis.

• | Fuel saturation of the evaporative emission (EVAP) canister

• | Exhaust leaks near the HO2S

• | Engine vacuum leaks

⇒ | If you find any of the above conditions, repair as necessary.

9. If all circuits/connections test normal, replace the appropriate HO2S.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

• | Control Module References for engine control module replacement, setup, and programming