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 provide an overview of each diagnostic category.

### DTC Descriptors

DTC P2231: HO2S Signal Circuit Shorted to Heater Circuit Bank 1 Sensor 1
DTC P2234: HO2S Signal Circuit Shorted to Heater Circuit Bank 2 Sensor 1

### Circuit Description

The engine control module (ECM) supplies a voltage near 450 mV between the heated oxygen sensor (HO2S) signal circuit and the low reference circuit. The HO2S varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean. The ECM monitors and stores the HO2S voltage information. The ECM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. Or, to detect if the HO2S signal voltage switches at the same rate at which the ECM is commanding the heater ON and OFF.

### Conditions for Running the DTC

• | Before the ECM can report that DTC P2231 or P2234 failed, DTCs P0030, P0031, P0032, P0050, P0051, P0052, P0133, P0135, P0153, and P0155 must run and pass.

• | DTCs P0030, P0031, P0032, P0050, P0051, P0052, P0116, P0117, P0118, P0119, P0125, P0133, P0135, P0153, P0155, P0201, P0202, P0203, P0204, P0205, P0206, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, and P0277 are not set.

• | The engine is operating.

• | The ignition voltage is greater than 10 volts.

• | The calculated exhaust gas temperature is between 600-800°C (1,112-1,472°F).

• | The engine coolant temperature (ECT) during the previous ignition cycle was greater than 60°C (140°F).

• | The ECT at engine start is less than 40°C (104°F).

• | The HO2S heater control is enabled for greater than 5 seconds.

• | DTC P2231 and P2234 run continuously once the conditions above exist for greater than 90 seconds.

### Conditions for Setting the DTC

DTC P2231 or P2234 will set when any of the following conditions exist.

• | The ECM detects that the HO2S signal voltage increases more than 2 volts in 4 out of 6 HO2S heater switch OFF samples.

• | The primary HO2S voltage is between 600-1,008 mV and the corresponding secondary HO2S voltage is less than 100 mV for greater than 4 seconds or for a cumulative of 50 seconds.

• | The primary HO2S voltage is between 60-400 mV and the corresponding secondary HO2S voltage is less than 500 mV for greater than 4 seconds or for a cumulative of 50 seconds.

### Action Taken when the DTC Sets

DTCs P2231 and P2234 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P2231 and P2234 are Type B DTCs.

### Diagnostic Aids

• | The HO2S voltage should be between 350-550 mV with the ignition ON. If the voltage is more than the specified value, there is a condition with the HO2S circuits. If the voltage does not change after disconnecting the HO2S, the condition is between the sensor and the ECM. If the voltage is between 350-550 mV after disconnecting the sensor, the condition is with the HO2S.

• | Inspect the HO2S harness connector for water intrusion. Moisture in a connector may cause voltage to bleed to other circuits within the connector.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

1. Ignition ON, observe the appropriate scan tool HO2S voltage parameter. The reading should be less than 1,025 mV.
2. 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

1. Ignition OFF, disconnect the harness connector of the appropriate HO2S.
2. Ignition ON, verify the HO2S parameter is between 350-500 mV.

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

3. If all circuits/connections test normal, replace the applicable HO2S.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

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