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.
- Ignition OFF, disconnect the X2 harness connector at the K47 Rear
Differential Clutch Control Module.
- 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
- 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.
- Ignition OFF, disconnect the X2 harness connector at the K47 Rear
Differential Clutch Control Module,
Ignition ON/Vehicle in Service Mode.
- 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
- Ignition OFF, disconnect the X2 harness connector at the K47 Rear
Differential Clutch Control Module.
- 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
- 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.
- Ignition OFF, disconnect the X2 harness connector at the K47 Rear
Differential Clutch Control Module,
Ignition ON/Vehicle in Service Mode.
- 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.
READ NEXT:
Strategy Based Diagnostics
Review the system operations in order to familiarize yourself with the system
functions. Refer to Rear Drive Axle
Description and Operation, and Power Transfer Unit Case De
Removal Procedure
1. Prepare the control module for removal using the SPS programming support
tool.
NOTE: The rear differential clutch control module can now be removed
and replaced.
2. Raise and su
SEE MORE:
Removal Procedure
WARNING: Brake Dust Warning.
WARNING: Brake Fluid Irritant Warning.
CAUTION: Brake Fluid Effects on Paint and Electrical Components Caution
NOTE: Always replace disc brake pads in axle sets.
1. Inspect the fluid level in the brake master cylinder reservoir.
2. If the brake fluid l
Touch and the following may
display:
Auto Memory Recall
Easy Exit Driver Seat
Chime Volume
Hands Free Liftgate Control
Reverse Tilt Mirror
Extended Hill Start Assist
Auto Wipe in Reverse Gear
Auto Memory Recall
This feature automatically recalls
the current driver's previously stored
1 or 2