The Powertrain Control/Emissions Diagnosis (PC/ED) manual has been revised for diagnosing electronic throttle bodies (ETBs). The ETC_ACT and ETC_DSD PIDs should not used to diagnose possible ETB concerns. The IDS has a limited refresh rate when reading these PIDs and cannot display quickly enough to validate a concern. The PCM automatically monitors these inputs more accurately and will set diagnostic trouble codes (DTCs) when appropriate. Using these PIDs for diagnostics will lead to inaccurate results and improper ETB replacements. If a concern is intermittent and no DTCs are present, refer to historical DTCs and the PC/ED, Section 3 No DTCs Present Index chart for further information.
full bulletin at NHTSA ↗2005 Mercury Grand Marquis engine problems
severe 8 complaints filed with NHTSA · avg repair $3,100 · see engine across all vehicles →
Complaints
8
Recalls
0
Avg fix
$3,100
2crashes
When does it fail?
Of the 8 engine complaints filed for the 2005 Mercury Grand Marquis, here's the actual mileage breakdown — failures cluster heaviest at 0-25,000 mi.
0-25k
25-50k
50-75k
75-100k
100-125k
125-150k
150k+
Each bar shows the share of total complaints filed at that mileage range. Peak failure window highlighted. Some owners report problems earlier; some make it well past 150,000 miles symptom-free. Maintenance habits and driving conditions shift the curve as much as mileage alone.
What stands out
Of the 4 model years of Mercury Grand Marquis we track for engine problems, this one carries the most owner complaints on file — 8.
No new NHTSA engine complaint has been filed on this vehicle in over 20 years — the issue may be aging out of the active population.
Is there a fix? Manufacturer service bulletins
The manufacturer has issued service bulletins covering engine on this vehicle — documented repair instructions, service campaigns, or warranty extensions sent to dealers. A TSB isn't a recall (it's not a free safety remedy), but it's the manufacturer acknowledging the issue and how to fix it.
FORD/LINCOLN/MERCURY: IF BATTERY WAS DISCONNECTED OR DEAD, VEHICLES/TRUCKS MAY EXPERIENCE HARD STARTS AND ENGINE IDLE RPM FLUCTUATION AND EXHIBIT DIAGNOSTIC TROUBLE CODES (DTCS) P0505, P0506, P2111 AND P2112.
full bulletin at NHTSA ↗FORD/MERCURY/LINCOLN: VEHICLES MAY EXHIBIT ONE OR MORE OF THE FOLLOWING SYMPTOMS: DRIVE AWAY HESITATION, LOSS OF RPM ON DECELERATION, DIFFICULTY STARTING, AND/OR IDLE RPM LESS THAN DESIRED. THE F53 MOTORHOME CHASSIS IS INCLUDED.
full bulletin at NHTSA ↗SOME 1997-2008 VEHICLES EQUIPPED WITH A 4.6L 2V, 5.4L 2V, OR 6.8L 2V ENGINE--SPARK PLUG THREAD REPAIR PROCEDURE--NOT COVERED UNDER NEW VEHICLE LIMITED WARRANTY. THIS INCLUDES F-53 MOTORHOME CHASSIS. UPDATED 2/23/10.
full bulletin at NHTSA ↗WDS COP KIT DIAGNOSTIC TIP - COIL ON PLUG (COP) IGNITION SYSTEMS - ENGINE MISFIRE OR ROUGH RUNNING.
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
What owners are reporting 3 most recent
On three occasions when shifting from park to reverse the engine sped up (accelerated drastically) causing the wheels to spin and only by quick application of the brake was an incident avoided. I drove into a parking space, put the car in park, then not satisfied with the position I attempted to back up, that's when the car accelerated. *jb
Rough engine idle, dealer reps say "all the new ones do it", "it's normal". I have asked them about it on several occasions since purchasing the car. My 2005 marquis does not get nearly the good gas mileage the 2001 marquis did with the same engine. The dealer told me "you can't compare cars". *nm
Rough engine idle, dealer reps say 'all the new ones do it', 'it's normal'. I've asked them about it on several occasions since purchasing the car. Not nearly as good gas mileage as our 2001 grand marquis got, was told by the dealer, "you can't compare cars'. *nm
Had engine trouble with your 2005 Mercury Grand Marquis?
File a complaint with NHTSA → It's free, official, and how every report above got here — owner filings are the federal safety record this page is built on.
Common questions
How serious is the engine problem on the 2005 Mercury Grand Marquis?
It's a meaningful issue. 8 complaints have been filed and the failure mode causes operational problems for owners. Repairs average $3,100.
At what mileage does the engine typically fail?
Based on the 8 complaints filed, engine issues most often appear around 47,765 miles. Some report problems earlier; some make it well past 150,000 with no symptoms. Maintenance habits matter — vehicles that received timely fluid services and were not regularly overworked tend to last longer.
What does it cost to fix?
Independent shops typically charge around $3,100 for engine repairs on this vehicle. Dealer pricing tends to run 20-40% higher. The exact figure depends on the specific failure mode, parts availability, and your local labor rates. If you're outside factory warranty, an extended service contract often covers this category.
Are there any recalls related to engine?
No active recalls currently cover engine issues on this vehicle. The complaints filed represent owner-reported failures that haven't risen to the level of a manufacturer-issued recall — but they're still worth knowing about before you buy or budget for repairs.
Related
Complaint and recall data sourced from the National Highway Traffic Safety Administration (NHTSA)
public records database. Verify the raw federal record at
nhtsa.gov/vehicle/2005/Mercury/Grand Marquis.
Severity ratings are derived from reported crashes, fires, injuries, and fatalities. Repair cost estimates are
independent-shop national averages and may differ in your area. Some links on this page are affiliate links.