Buick Regal Owners & Service Manuals

Buick Regal: Symptoms - Rear Differential Carrier

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 Description and Operation. All diagnosis on a vehicle should follow a logical process. Strategy based diagnostics is a uniform approach for repairing all systems. The diagnostic flow may always be used in order to resolve a system condition. The diagnostic flow is the place to start when repairs are necessary. For a detailed explanation, refer to Strategy Based Diagnosis.

Visual/Physical Inspection

  • Inspect for aftermarket devices, which could affect the operation of the vehicle. Checking Aftermarket Accessories
  • Inspect the easily accessible or visible system components for obvious damage or conditions, which could cause the symptom.
  • Check for the correct lubricant level and the proper viscosity.
  • Verify the exact operating conditions under which the concern exists. Note factors such as vehicle speed, road conditions, ambient temperature, and other specifics.
  • Compare the driving characteristics or sounds, if applicable, to a known good vehicle and make sure you are not trying to correct a normal condition.
  • Inspect for all-wheel drive activation and operation.
  • Factors that may contribute to an inoperative rear differential include:
    • Low gear oil levels
    • Differential inoperative due to antilock brake system (ABS) function
    • Inoperative powertrain control module (PCM) and/or wiring system
    • A mini-spare or different size tire installed
    • A fluid over-temperature condition
    • An inoperative or "stuck" clutch pump check valve
    • A defective rear differential assembly
    • An inoperative transfer case assembly


Test the vehicle under the same conditions that the customer reported in order to verify the system is operating properly.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom:

  • Symptoms - Vehicle
  • Noisy in Drive
  • Noisy When Coasting
  • Intermittent Noise
  • Constant Noise
  • Noisy on Turns
  • Rear Differential Carrier Leak Diagnosis


Functional Test

Rear axle activation and operation may be checked by positioning the four wheels off the ground, starting the vehicle, fully applying the parking brake, and selecting the drive position.

CAUTION: Avoid rear differential damage. Do not exceed 20 percent accelerator pedal application or apply throttle for more than 5 seconds while the parking brake is applied.

Lightly depress the accelerator pedal while watching the rear wheels. They will rotate slightly as the drive line winds-up. This indicates the all wheel drive (AWD) is functioning.


Rear Drive Axle

Rear Drive Axle


Rear Drive Axle


Rear Drive Axle


Rear Drive Axle

Rear Drive Axle


Rear Drive Axle


Definition: A visible indication of an external fluid leak from the rear diffrerential carrier assembly.

Review the Symptoms - Rear Differential Carrier and perform the necessary inspections. See below for suggested diagnostic method (s).

Special Tools

  • GE-28431-6 Fluorescent Oil Dye
  • GE-42220 Leak Detection Lamp 12V

Equivalent regional tools:Special Tools


1. Thorougly clean the suspected leak area using a rag and approved cleaner.

2. Detect the source of the leak:

Fluorescent Dye Method

  1. Add GE-28431-6 Fluorescent Oil Dye to the rear differential clutch or differential lubricant to determine the source of the leak.

NOTE: Do not drive the vehicle on the freeway as this will splatter oil, inhibiting leak diagnosis.

  1. Operate the vehicle for 15 - 20 minutes under city driving conditions until normal operating temperatures are reached.
  2. Shut OFF the engine.
  3. Inspect for the presence of dye within the oil leak using the GE-42220 Leak Detection Lamp 12V or equivalent. A presence or non

Powder Method

  1. Apply an aerosol type leak tracing powder to the suspected leak area.

NOTE: Do not drive the vehicle on the freeway as this will splatter oil, inhibiting leak diagnosis.

  1. Operate the vehicle for 15 - 20 minutes under city driving conditions until normal operating temperatures are reached.
  2. Shut OFF the engine.
  3. Trace the leak path through the powder in order to find the source of the leak.

3. Use the cause and correction below to determine the repair.

Rear Drive Axle

Rear Drive Axle

Rear Drive Axle


     Repair Instructions

     Rear Differential Clutch Control Module Replacement

    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

     Differential Clutch Oil Inspection

    1. Raise and support the vehicle. 2. Clean the area around the rear axle fill plug. 3. Place a drain pan under the vehicle. 4. Differential Clutch Cover Plug(1) - Remove. 5. Rear Axle Housing Fi


     Repair Instructions

    Outside Rearview Mirror Replacement Preliminary Procedures Front Side Door Window Garnish Molding Replacement. Outside Rearview Mirror Bolt [3x] CAUTION: Fastener Caution. Tighten 9 N.m (80 lb in) Outside Rearview Mirror Procedure Disconnect the electrical connector. Unlock the retainin

     DTC B25F8 or B25F9

    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 Descriptors D

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