Which parts fail
Components named in complaints (accelerator pedal, throttle, sudden acceleration, cruise control).
Mileage when the problem started
Owner reports
Selected complaints filed with NHTSA by 2003 Mercury Grand Marquis owners, lightly cleaned up (personal details are redacted by NHTSA).
I started Mercury with foot on break like normal. Shifted into reverse. Car accelerated backwards at full speed. Brakes did not stop car. Attempted to shift into neutral but went into drive instead. Car accelerated forward at full speed with my foot still on break. Car hit metal post and tree knocking them down and dragging the tree 50 to 60 feet before stopping with my foot still on the break. Car had stopped accelerating. I turned off the ignition. This unintended acceleration had happened before. Two different dealers attempted to fix the problem. Both of them thought they had been successful but it happened again. Previously, applying the brakes stopped the car, but not this time. Someone could have been injured severely or killed.
Sudden acceleration in a 2003 Mercury Grand Marquis. This happened after putting the vehicle in drive, it took off at an excessive rate of speed crossed a street and jumped two curbs about 15 inches high within 5 or 6 seconds. My thoughts were "what is happening?" & "brake or you are going to die" thank god this vehicle drown in hurricane katrina. I called your ofc in 2004 after this happened and was sent a form to fill out and return to you which I never did. However, with the Toyota recall it disturbs me that my Ford did the same thing. An investigation needs to be made as to why these things are happening because in my case it was not a floor mat and neither was it driver's error. It is important to myself that this incident is reported and hopefully someone will take it serious and find out what the real problem is before more lives are lost. …
Dt*: the contact stated while parked with the ignition on; the vehicle suddenly lurched forward without warning. The brakes were depressed and the ignition was turned off, which stopped the vehicle after it traveled 60 ft. This had occurred on numerous occasions. Also, while traveling 60 MPH with the cruise control engaged, the vehicle sped uncontrollably to 80 MPH. The brakes were depressed, but did not disengage the cruise control. Also, while traveling 40 MPH, the vehicle accelerated suddenly, causing the contact to drive the vehicle into a ditch to avoid an accident. The contact sustained a bruise to the shoulder. The manufacturer was contacted, and provided no assistance since the vehicle was out of warranty. The vehicle was taken to a service dealer twice, where the cruise control was replaced, but the problem persisted.
Tl* the contact owns a 2003 Mercury Grand Marquis. While traveling at 4 MPH, the contact applied the brakes and the vehicle independently accelerated. The contact crashed into another vehicle as a result. There were no injuries. On a later date, while parking in a residential garage, the contact depressed the brakes and the vehicle abnormally accelerated. The vehicle crashed into the garage wall and through the master bathroom of the home. The contact sustained injuries to her pelvis from attempting to apply extreme force to the brake. A police report was available. The vehicle was not diagnosed for the unintended acceleration failure. The failure mileage was 50,000 and the current mileage was 90,000.
Tl* the contact owns a 2003 Mercury Grand Marquis. The contact started the ignition with the brake pedal depressed and suddenly the vehicle unintendedly accelerated when the gear lever was shifted into drive. The brake pedal was engaged numerous times and the vehicle failed to slow down and crashed into the nearby garage and also crashed into a parked vehicle. A police report was filed of the incident. The driver sustained injury to the left knee. The vehicle was completely destroyed and towed to an authorized dealer. The manufacturer was not notified of the unintended acceleration malfunction. The approximate failure mileage was 100,000. The VIN was unavailable.
Tl* the contact owns a 2003 Mercury Grand Marquis. The contact stated that while stopped, the engine rpms increased excessively as the vehicle violently accelerated without warning. The contact crashed into another vehicle. There were no injuries and a police report was filed of the incident. The vehicle was taken to a dealer where the failure was unable to be duplicated or diagnosed. The manufacturer was notified of the failure. The vehicle was not repaired. The approximate failure and current mileage was 147,696.
Tl* the contact owns a 2003 Mercury Grand Marquis. The contact stated was attempting to park the vehicle while driving 5 MPH in a residential driveway when the vehicle abnormally accelerated. The contact crashed into the garage of his home. The brakes were applied during the failure but did not respond. The contact was uninjured yet there was extensive damage to the vehicle. The vehicle had not yet been inspected or repaired. The manufacturer was not notified of the failure. The failure mileage was 50,400.
Tl contact owns a 2003 Mercury Grand Marquis. While waiting to turn at a stop sign the engine increased in rpms and accelerated forward. The failure caused the contact's vehicle to crash into the vehicle in front of him. Both vehicles were damaged , and a police report was taken. The vehicle was at the dealer awaiting a diagnostic to determine the cause of failure. The contact was waiting for an insurance estimate and report. The current and failure mileages were 58,000.
The engine revved in full throttle when the gear shifter was shifted into drive from park; resulting in a rear end collision. This occurred while in stop and go traffic in the car wash line. The repair shop failed to determined what caused the failure, but the consumer feels due through their own research that it was caused by the electrical system/cruise control.
Consumer complained about sudden acceleration. Consumer was in a parking lot and put the vehicle in drive. Did not press the accelerator, and vehicle jumped the curb and flattened two tires.consumer had the vehicle towed to a body shop.
Acceleration complaints in other Grand Marquis years
Frequently asked questions
How common are acceleration problems on the 2003 Mercury Grand Marquis?
NHTSA has 27 complaints about the speed control & acceleration of the 2003 Mercury Grand Marquis, 7% of the model year's 362 complaints. The component named most often is accelerator pedal (6 mentions).
Is there a recall for 2003 Mercury Grand Marquis acceleration problems?
No. NHTSA lists no speed control & acceleration recall for the 2003 Mercury Grand Marquis, though it has 1 recall for other components. If the problem is widespread, a repair may still be covered by an extended warranty or a manufacturer service bulletin — ask a dealer.
At what mileage do 2003 Mercury Grand Marquis acceleration problems start?
Half of the complaints with a recorded mileage happened before about 25,000 miles, and 47% before 25,000 miles.
Is it dangerous?
Owners linked 13 crashes, 0 fires and 7 injuries to speed control & acceleration problems on this model year. If you notice symptoms, have the car checked before driving further.
Source: U.S. National Highway Traffic Safety Administration (NHTSA) — owner complaints through October 20, 2026, recalls and defect investigations; fuel economy from the EPA. Complaints are unverified reports and are not proof of a defect. How we rate model years.