Buick Regal: DTC C12A1 or C12A9

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 C12A1

Right Rear Differential Clutch Solenoid Valve Control Circuit.

DTC C12A9

Left Rear Differential Clutch Solenoid Valve Control Circuit.

For symptom byte information, refer to Symptom Byte List.

Diagnostic Fault Information

Circuit/System Description

The right and left rear differential clutch solenoid valves are an electro-hydraulic valve used to relieve pressure in the hydraulic system for safety reasons. When the valves are energized, the valves are closed and hydraulic pressure can be accumulated. When the valves are de-energized, the valves are open and it is not possible to build hydraulic pressure.

Conditions for Running the DTC

• The engine is running.
• The engine speed is above 400 rpm.

Conditions for Setting the DTC

C12A1 00

• The right valve high side voltage monitor signal is significantly greater than 0 V.
• The right valve low side voltage monitor signal is close to 0 V.

C12A9 00

• The left valve high side voltage monitor signal is significantly greater than 0 V.
• The left valve low side voltage monitor signal is close to 0 V.

Action Taken When the DTC Sets

One or more of the following actions may occur:

• The electronic limited slip system is temporary inhibited for the duration of the key cycle.
• Symptom bytes 00 will display the AWD SERVICE message in the driver information center.

Conditions for Clearing the DTC

• The condition for the DTC is no longer present.
• The DTC is not detected in 40 consecutive drive cycles.

Reference Information

Schematic Reference

Rear Axle Wiring Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEW INDEX

Description and Operation

Rear Drive Axle Description and Operation

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the Q49 Rear Differential Clutch Solenoid Valve, Ignition ON/Vehicle in Service Mode.

2. Test for 5.6 - 6.4 V between the control circuit terminal 3 and ground.

• If less than 5.6 V

1. Ignition OFF, disconnect the X2 harness connector at the K47 Rear Differential Clutch Control Module.
2. Test for infinite resistance between the control circuit terminal 3 and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the control circuit terminal 3 end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K47 Rear Differential Clutch Control Module.

• If greater than 6.4 V

1. Ignition OFF, disconnect the X2 harness connector at the K47 Rear Differential Clutch Control Module, Ignition ON/Vehicle in Service Mode.
2. Test for less than 1 V between the control circuit terminal 3 and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K47 Rear Differential Clutch Control Module.

• Go to next step: If between 5.6 - 6.4 V

3. Test for 4.9 - 5.3 V between the control circuit terminals listed below and ground.

• Control Circuit Terminal 2
• Control Circuit Terminal 1
• If less than 4.9 V

1. Ignition OFF, disconnect the X2 harness connector at the K47 Rear Differential Clutch Control Module.
2. Test for infinite resistance between the appropriate control circuit terminal and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the appropriate control circuit terminal end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K47 Rear Differential Clutch Control Module.

• If greater than 5.3 V

1. Ignition OFF, disconnect the X2 harness connector at the K47 Rear Differential Clutch Control Module, Ignition ON/Vehicle in Service Mode.
2. Test for less than 1 V between the appropriate control circuit terminal and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K47 Rear Differential Clutch Control Module.

• Go to next step: If between 4.9 - 5.3 V

4. Test or replace the Q49 Rear Differential Clutch Solenoid Valve.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Differential Carrier Assembly Replacement
• Control Module References for control module replacement, programming, and setup.

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