C1991 on Ford: How to Diagnose & Fix
Lane Departure Warning System Fault
1 Ford model · 1 documented issue · $300-$1,500 repair
C1991 on Ford by model: symptoms, diagnosis and fix
The 2003-2017 Ford Expedition with optional air suspension (standard on Eddie Bauer, King Ranch, Platinum, and EL/MAX trims) suffers from air suspension compressor failure, air spring leaks, and ride height sensor malfunctions. The compressor, located under the vehicle, is exposed to road debris, salt, and moisture which degrades the motor and valves. When air springs develop leaks, the compressor runs continuously trying to maintain ride height, leading to premature burnout. RepairPal estimates compressor replacement between $666 and $724, though dealer pricing can reach $1,200. NHTSA has received hundreds of complaints regarding air suspension failures. Strutmasters.com notes that 2007-2011 Expedition and Navigator share the same air suspension system and failure patterns. Many owners opt for air-to-coil spring conversion kits as a permanent, lower-cost solution.
Common Symptoms
- Rear of vehicle sagging or sitting noticeably lower
- Air suspension warning light or message on dash
- Compressor runs excessively or continuously
- Loud compressor noise from under the vehicle
- Harsh ride over bumps
- Vehicle leans to one side
- Hissing sound from air springs or compressor
- Vehicle bottoming out on speed bumps or driveway transitions
How to Fix
Most cost-effective permanent fix is an air-to-coil spring conversion kit from Strutmasters or Arnott ($300-500 for kit plus installation). If keeping air suspension: replace the compressor (Arnott P-2936 or Dorman 949-200, $200-400 part), both rear air springs ($150-250 each), and inspect all air lines for cracks. Always replace air springs in pairs. Compressor relay should also be checked - a corroded relay causes intermittent compressor operation. RepairPal estimates $666-724 for compressor replacement at a shop.
Sources for this issue (1)
C1991 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does C1991 mean on a Ford?
C1991 stands for "Lane Departure Warning System Fault." This is a manufacturer-specific chassis/safety code indicating a fault in the Lane Departure Warning (LDW) system. Lane departure warning uses a forward-facing camera (and on some vehicles related modules) to detect lane markings and alert the driver if the vehicle drifts out of its lane. C1991 sets when the system's module detects an internal failure, a sensor/camera problem, or a condition that prevents reliable operation. The lane-departure feature may be disabled and a warning indicator may appear, while basic driving is unaffected. On Ford it is documented across 1 model: Expedition.
What are the most common causes of C1991?
The most common causes of C1991 are: Blocked, misaligned, or dirty forward camera/sensor, Faulty lane departure warning camera or module, Windshield replacement requiring camera recalibration, Wiring or connector fault to the camera/module, Low system voltage or power/ground issue, Software/calibration fault needing an update or relearn, Communication (network) fault with the camera module. The specific cause varies by vehicle.
How much does it cost to fix C1991 on a Ford?
Published repair estimates on Ford range from $300 to $1,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for C1991 on a different make?
View C1991 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.