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 P2096: Post Catalyst Fuel Trim System Low Limit Bank 1
DTC P2097: Post Catalyst Fuel Trim System High Limit Bank 1

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HO2S Signal | P0131, P0137 | P0134, P0140 | P0132, P0138 | P0133, P0139, P2096, P2097
Low Reference | -- | P0134, P0140 | P0132, P0138 | P0133, P0139, P2096, P2097

### Typical Scan Tool Data

#### HO2S 1 and 2

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.
HO2S 1 and 2 Signal | 0 mV | 400-415 mV | 1000 mV
Low Reference | -- | 400-415 mV | 1000 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.

The HO2S utilizes the following circuits:

• | A signal circuit

• | A low reference circuit

• | An ignition 1 voltage circuit

• | A heater control circuit

### Conditions for Running the DTC

• | The engine is running.

• | The ignition 1 voltage is greater than 10 volts.

• | The barometric pressure is greater than 72 kPa.

• | The intake air temperature (IAT) sensor parameter is less than -40°C (-40°F).

### Conditions for Setting the DTC

Long term fuel trim adjustment has reached its limit while the sensor voltage is still trying to move the adjustment further in the same direction.

### Action Taken when the DTC Sets

DTCs P2096 and P2097 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P2096 and P2097 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. Ignition ON, observe the DTC information with a scan tool. DTC P0131, P0132, P0134, P0137, P0138, or P0140 should not be set

⇒ | If a DTC is set, refer to DTC P0131, P0132, P0134, P0137, P0138, or P0140 for further diagnosis.

2. Allow the engine to reach operating temperature. Operate the vehicle within the parameters specified in Conditions for Running the DTC. The DTC should not set.
3. 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. Verify that none of the following conditions exist:

• | Inspect the HO2S 1 and HO2S 2 for being secure

• | Damaged wiring between either HO2S and the ECM

• | Water intrusion in the HO2S harness connector

• | Lean or rich fuel injectors--Refer to Fuel Injector Solenoid Coil Test.

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

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

• | Contaminated HO2S--For example, silicon

• | Exhaust leaks near the HO2S

• | Engine vacuum leaks

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

2. Ignition OFF, disconnect the harness connector at the HO2S 2.
3. Ignition ON, verify the scan tool HO2S 2 voltage parameter is between 350-550 mV.

⇒ | If less than the specified range, test the HO2S 2 high signal circuit for a short to ground. If the circuit/connections test normal, replace the ECM.

4. Connect the harness connector at the HO2S 2.
5. Engine idling, raise the engine speed above 1,200 RPM for 30 seconds. Verify the scan tool HO2S 2 voltage parameter is greater than 60 mV.

⇒ | If less than the specified range, replace the HO2S 2.

6. Engine idling, move the HO2S 1 and HO2S 2 harnesses between the HO2S harness connector and the ECM. Observe the scan tool HO2S 1 and 2 voltage parameter. Verify neither parameter changes abruptly.

⇒ | If the parameter changes abruptly, repair the harness/connections as necessary.

7. If all circuits/connections test normal, replace the HO2S 1.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor 1 Replacement

• | Heated Oxygen Sensor 2 Replacement

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