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 C1209: Left Rear Wheel Speed Sensor Circuit High
DTC C1223: Left Rear Wheel Speed Sensor Circuit
DTC C1227: Left Rear Wheel Speed Sensor Circuit Range/Performance
DTC C1234: Left Rear Wheel Speed Sensor Circuit Low

### Circuit/System Description

The wheel speed sensor receives a 12-volt power supply voltage from the electronic brake control module (EBCM) and provides an output signal to the EBCM. As the wheel spins, the wheel speed sensor sends the EBCM a DC square wave signal. The EBCM uses the frequency of the square wave signal to calculate the wheel speed. If the EBCM identifies an error, it sets a code and communicates via GMLAN to the engine control module (ECM).

### Conditions for Running the DTC

Ignition voltage is between 9 and 16 volts.

### Conditions for Setting the DTC

• | The engine must be ON.

• | The vehicle speed is greater than 16 km/h (10 mph).

### Action Taken when the DTC Sets

DTCs C1209, C1223, C1227 and C1234 are type C DTCs.

### Conditions for Clearing the MIL/DTC

DTCs C1209, C1223, C1227 and C1234 are type C DTCs.

### Reference Information

#### Schematic Reference

• | Engine Controls Schematics .

• | Antilock Brake System Schematics .

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing .

• | Testing for Intermittent Conditions and Poor Connections .

• | Wiring Repairs .

#### Scan Tool Reference

Control Module References

### Circuit/System Verification

The ECM sets DTCs C1209, C1223, C1227 and C1234 in conjunction with the EBCM, any EBCM wheel speed sensor DTCs should be diagnosed ahead of performing the test below.

### Circuit/System Testing

1. Verify that no other DTCs are set.

⇒ | If any other DTCs are set, refer to Diagnostic Trouble Code (DTC) Type Definitions .

2. Ignition ON, using a scan tool view the current DTC's.

⇒ | If any of the following DTCs C1209, C1223, C1227 or C1234, are set to current replace ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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