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 Descriptor

DTC P0040: O2 Sensor Signals not Plausible (Bank 1 Sensor 1 & Bank 2 Sensor 1)
DTC P0041: O2 Sensor Signals not Plausible (Bank 1 Sensor 2 & Bank 2 Sensor 2)

### Circuit Description

The heated oxygen sensor (HO2S) heater reduces the time required for the oxygen sensor to reach operating temperature and maintains the operating temperature during extended idle periods. When the ignition is turned to the ON position, ignition voltage is supplied directly to the sensor heater. The engine control module (ECM) controls the heater operation by first modulating the control circuit to ground when the sensors are cold. This prevents the possibility of thermal shock to the sensor from condensation build-up on the sensor, by controlling the sensors rate of heating. After a predetermined amount of time the ECM commands the heaters ON continuously. Once the sensor reaches operating temperature the ECM may modulate the heater control circuit to ground, to maintain a desired temperature.

The ECM controls the heater by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit that is pulled-up to voltage. The ECM can determine if the control circuit is open, shorted to ground or shorted to a voltage by monitoring the feedback voltage.

An HO2S Signal Swapped DTC set if the ECM detects the HO2S signal voltages are heading in the opposite direction of the commanded state.

### Conditions for Running the DTC

#### P0040 or P0041

• | The ignition voltage is between 10-18 volts.

• | The engine speed is greater than 80 RPM.

• | The HO2S heater is commanded ON and OFF at least once during the ignition cycle.

• | The DTCs run continuously once the above conditions are met for 1 second.

### Conditions for Setting the DTC

#### P0040 or P0041

An HO2S Signal Swapped DTC set if the ECM detects the HO2S signal voltages are heading in the opposite direction of the commanded state.

### Action Taken When the DTC Sets

DTCs P0040 and P0041 are type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0040 and P0041 are type B DTCs.

### Diagnostic Aids

• | If the condition is intermittent, move the related harnesses and connectors with the engine operating, while monitoring the circuit status for the component with a scan tool. If the circuit status parameter changes from OK or Indeterminate to Fault there is a condition with the circuit or a connection.

• | An open fuse in the HO2S heater circuit may be caused by the heater element in one of the sensors. The condition may not be present until the sensor operates for a period of time. If no fault is present in the heater circuit, monitor the amperage of each heater using the DMM to determine if one of the heater elements is the cause of the open fuse. Inspect the sensor pigtail or the harness for contacting the exhaust system.

### 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 at operating temperature for at least 30 seconds. Increase the engine speed to 2000 RPM. Observe the DTC information with a scan. DTCs P0040 or P0041 should not set.

⇒ | If a DTC sets, inspect the appropriate HO2S harnesses for being connected to the correct sensor.

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.

### 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 1 Sensor 2 .

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 .

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 .

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