There are 2 owner-reported powertrain & transmission complaints for the 2008 Mercury Grand Marquisin NHTSA's database. These are unverified consumer reports and may not reflect confirmed defects.
THE CAR WILL SUDDENLY AND WITHOUT WARNING ACCELERATE TO 5000 RPM'S. HAD THROTTLE BODY AND MAS REPLACED WHICH SEEMED TO HELP. HOWEVER, IT STILL HAPPENS ONCE IN A WHILE (ONCE EVERY 3 WEEKS AVERAGE). USUALLY HAPPENS AFTER SHIFTING FROM PARK TO DRIVE AND DRIVING FORWARD AT LOW SPEEDS (AROUND 5-10 MPH). HASN'T HAPPENED AT HIGHER SPEEDS. WAS TOLD BY ONE MECHANIC THAT THE COMPUTER IS DEFECTIVE???.
TL* THE CONTACT OWNS A 2008 MERCURY GRAND MARQUIS. WHILE DRIVING 25 MPH AND ENTERING A DRIVE-THRU LANE AT A BANK, THE CONTACT ATTEMPTED TO SHIFT THE VEHICLE INTO PARK; HOWEVER, THE GEAR FAILED TO SHIFT. THE CONTACT ENGAGED THE EMERGENCY BRAKE TO STOP THE VEHICLE. THE CONTACT STATED THAT THE GEAR SHIFTER FAILURE WAS ALSO EXPERIENCED IN APPROXIMATELY 2016. THE VEHICLE WAS TOWED TO MALLOY FORD (1911 VALLEY AVENUE, WINCHESTER, VA 22601, (540)-667-4434) AND REPAIRED, BUT THE FAILURE RECURRED. THE VEHICLE WAS THEN TOWED TO A REPAIR SHOP WHERE IT WAS DIAGNOSED THAT THE GEAR SHIFTER CABLE FAILED. THE GEAR SHIFTER CABLE WAS REPLACED AND THE VEHICLE WAS REPAIRED. THE MANUFACTURER WAS NOT CONTACTED. THE FAILURE MILEAGE WAS 128,000. **TR CONSUMER STATED THE SHIFT CABLE FAILURE PREVENTS THE DRIVER FROM SHUTTING OFF THE CAR AND KEEPS IT IN GEAR AND MOVING OF THE CAR UNLESS THE BRAKE IS DEPRESSED! TRANSMISSION SHIFT CABLE WAS REPLACED 2 TIMES. UPDATED 11/8/18*JB
Complaints are unverified consumer reports submitted to NHTSA. A high complaint count may reflect vehicle popularity, not defect severity. Data sourced from NHTSA public records.
Data synced from NHTSA on Apr 26, 2026