U0199 Code: Lost Communication With Door Control Module "A"
The door module (usually the driver's door) went silent; windows, mirrors and locks on that door may quit.
At a glance
Severity: Low
- Meaning
- Lost Communication With Door Control Module "A"
- System
- Module Communication · Network
- Safe to drive?
- Yes, short term
- Typical repair cost
- $5–$700
- DIY difficulty
- Moderate
U0199 is set by the body module or other door modules when door control module "A" stops sending messages. On most vehicles "A" is the driver's door module, mounted inside the door panel, often attached to the window regulator motor, and it controls that door's window, lock, mirror adjustment and folding, puddle lamp and the master window switch for the other doors. The wires to it run through a rubber boot between the door and the body pillar, and after tens of thousands of openings the copper strands can break right at that bend. Water getting past a torn door vapor barrier onto the module and a blown door module fuse are the other common causes.
Can I keep driving? Safe to drive. The main annoyances are a window you can't close, a door that won't lock and a mirror you can't adjust; if the window is stuck open, secure the car and cover the opening before parking outside.
How to read U0199
- U Network
- 0 Generic (SAE)
- 1 Module Communication
- 99 Specific fault
Symptoms
- Driver's window won't go up or down
- Master switch can't control the other windows
- Driver's door doesn't lock or unlock with the fob or switch
- Mirror adjustment, folding or mirror heating dead
- Everything works only when the door is held at a certain angle
- Door lights or warning lamp in the door not working
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Broken wires in the rubber boot between door and pillar from repeated opening and closing
- Water in the door reaching the module after the vapor barrier tore or door drains clogged
- Internal door module failure (often combined with the window motor)
- Blown door module fuse or poor power/ground
- Low battery voltage or a recent battery disconnect
Diagnosis step by step
Confirm which door is module "A"
Check the scan tool's module list; on most vehicles "A" is the driver's door. See whether other door modules also report the fault, which would point to a shared network or supply issue.
Tools: OBD-II scanner
Wiggle-test the door hinge boot
Open the door fully and slowly swing it while a helper operates the window or watches the module status in the scan tool. If functions come and go with the door angle, the harness in the boot is broken.
Tools: OBD-II scanner
Inspect the wires inside the boot
Unclip the boot from the pillar and door and slide it back. Look for cracked insulation, kinked or broken wires and green corrosion; broken strands often hide inside insulation that looks intact, so flex each wire gently.
Tools: Screwdriver, Flashlight
Check the fuse and power at the module
Test the door module fuse, then remove the door panel and measure battery voltage, ground and network signals at the module connector. Some door modules use a low-speed CAN that keeps limping along on one wire, so check both lines.
Tools: Multimeter, Screwdriver
Look for water in the door
With the panel off, check the plastic vapor barrier for tears and the door bottom drains for blockages. Water tracks on the module or its connector call for resealing the barrier as well as repairing the part.
Tools: Flashlight
Repair the harness or replace the module
Repair broken wires with soldered, heat-shrunk splices staggered along the bundle, or fit a repair harness section. If the wiring is sound, replace the module and run any window initialization so auto-up and pinch protection work.
Tools: Pliers, OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace door module fuse | Yes | $5–$60 |
| Repair wires in door hinge boot | Yes | $120–$350 |
| Reseal vapor barrier and clear door drains | Yes | $80–$200 |
| Replace door control module (incl. setup) | No | $250–$700 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Volkswagen
Broken wires in the driver's door boot are a well-known issue on older Volkswagen models such as the Jetta and Golf fourth generation and the Passat of that era, causing dead windows, locks and door module communication faults.
Emissions / smog test impact
Usually passes
U0199 doesn't affect emissions testing. It only matters in a safety inspection if it leaves a required feature, such as the driver's mirror, unusable.
Frequently asked questions
Why does my window only work when the door is half open?
That is the classic sign of broken wires in the rubber boot between door and body. The copper breaks at the bend, and contact is only made at certain door angles.
Can I fix the door wiring myself?
Many owners can with patience. Remove the boot, cut out the damaged section and solder in new wire with heat shrink, staggering the joints so they don't all flex in one place.
Which door is door control module "A"?
On most vehicles it is the driver's door, but the assignment is up to the manufacturer. The scan tool's module list will show the name used for your car.
Why did U0199 show up after a battery change?
Door modules can lose contact during a voltage dip and store a history code. If the code clears and everything works, no repair is needed, though the windows may need their one-touch function reset.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy