U0199 Lost Communication With Door Control Module "A"

U0199 sets when the reporting module stops receiving expected messages from a door control module. The module may be dead, unpowered, or simply unable to reach the network — the code cannot tell those apart on its own.

Code details

Generic OBD-II · U0

System: Computer
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not order a door control module on the strength of this code. Lost communication is a symptom of power, ground, wiring or network trouble far more often than it is a failed controller, and a replacement will be just as silent on a broken circuit.

Symptoms of U0199

Check-engine light, sometimes with several unrelated codes at once.
Warning lights, a no-start, or intermittent electrical faults.
Communication or module-reset problems on a scan tool.

Common causes of U0199

Low battery voltage, poor grounds, corroded connectors, or blown fuses.
Wiring or network (CAN bus) faults between modules.
A module software/programming issue, or rarely a failed controller.

Useful checks before replacing parts

Check power and ground at a door control module first, including its fuses and any relay that feeds it, because an unpowered module is silent in exactly the same way as a failed one.
Establish whether one module is missing from the network or several are, since a whole missing segment points at bus wiring or a gateway rather than at the named controller.
Load-test the battery and check charging voltage before anything else, because low system voltage drops modules offline and sets communication codes across unrelated systems.

Related OBD-II codes

These nearby computer entries can help compare wording and pin down the fault area.