2005 Pontiac Grand Prix

Grand Prix models equipped with the supercharged 3.8L Series III V6 (L32/L67) develop supercharger coupler wear, where the rubber isolator between the supercharger snout and the drive pulley strips and fails. This eliminates boost pressure and results in a significant power loss. The supercharger nose cone bearing also fails, producing a grinding or whining noise under boost.

Replace the supercharger coupler with an updated design. Aftermarket hardened couplers are available that last significantly longer than the OEM rubber coupler. If the nose cone bearing has failed, rebuild or replace the supercharger unit. The Eaton M90 supercharger can be rebuilt with new bearings, rotors, and seals by specialty shops.

The electric power steering system on the Grand Prix fails intermittently or permanently, with the 'Power Steering' warning appearing on the instrument cluster. The steering becomes extremely heavy and difficult to turn, particularly at low speeds. This was a persistent problem across multiple GM W-body and Epsilon platform vehicles during this era.

Replace the electric power steering motor and/or control module located on the steering column. GM issued TSBs addressing EPS motor and torque sensor failures. The torque sensor inside the steering column can also fail, providing incorrect input to the EPS control module. Flash the replacement module with the latest calibration.

The 3.8L V6 (both naturally aspirated and supercharged versions) is notorious for lower intake manifold gasket failure that allows coolant to leak externally or internally into the engine oil. The original Dex-Cool coolant is particularly aggressive on the factory gaskets. Symptoms include coolant loss, sweet smell, milky oil, overheating, and white exhaust smoke.

Replace the lower intake manifold gaskets with updated Felpro gaskets that are more resistant to Dex-Cool. Flush the cooling system and refill with fresh coolant. If coolant has contaminated the engine oil, perform multiple oil changes to flush the system. Inspect the upper intake manifold plenum for warping on supercharged models.

The power window regulators and motors fail, causing the windows to fall into the door, operate slowly, or stop working entirely. Owners often hear a clicking or grinding noise from inside the door panel when the window switch is pressed. The plastic guide clips on the regulator break, disconnecting the window glass from the lift mechanism. This is extremely common on W-body GM vehicles.

Replace the window regulator and motor assembly as a unit. The door panel must be removed to access the regulator. Secure the window glass with tape before removing the old regulator to prevent it from falling and shattering. Lubricate the new regulator tracks with white lithium grease. Both front regulators commonly fail within a short period of each other.

The ABS wheel speed sensors corrode and fail, triggering the ABS and traction control warning lights. In some cases, the Electronic Brake Control Module (EBCM) itself fails internally, disabling the ABS, traction control, and StabiliTrak systems. Owners report the ABS engaging unnecessarily during normal braking on dry pavement, causing a pulsating brake pedal and extended stopping distances.

Diagnose the ABS system to determine if the fault is a wheel speed sensor or the EBCM. Replace failed wheel speed sensors individually — they are located at each wheel hub. If the EBCM has failed, it can be sent to a specialized rebuilding service for repair at a lower cost than OEM replacement. Clean and inspect the tone rings on each wheel hub for damage or debris.