A blown fuse or poor connection in the power feed to the door control module.; Damaged, chafed, or corroded wiring in the flexible boot between the door and the body.; A faulty door control module itself, often due to water intrusion or internal circuit failure.; Loose or corroded connector pins at the module or at the body control module end of the CAN bus.; A shorted or open CAN bus wire that affects only the branch to that door module.; Low battery voltage or a weak charging system causing modules to drop offline intermittently.

DTC codes / U02xx · Lost communication with a control module / U0203

U0203Lost Communication With 'Door Control Module E'

Q: What does code U0203 mean?

Lost Communication With 'Door Control Module E'. U0203 means the vehicle's main computers have lost the controller area network (CAN) communication signal from a specific door control module designated as 'E'. The module that monitors the network detected that it stopped receiving the periodic status messages that this door module is supposed to broadcast.

U0203 means the vehicle's main computers have lost the controller area network (CAN) communication signal from a specific door control module designated as 'E'. The module that monitors the network detected that it stopped receiving the periodic status messages that this door module is supposed to broadcast.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaLost communication with a control module

Symptoms you may notice

The warning light (often a door ajar or network fault indicator) illuminates on the dashboard.
One or more doors may fail to lock or unlock with the central locking system or key fob.
The power window, mirror, or seat memory functions on the affected door may stop working.
The interior dome light may stay on or not come on when that door is opened.
Often no symptoms besides the warning light, especially if the module only drops communication intermittently.

Common causes, most likely first

A blown fuse or poor connection in the power feed to the door control module.
Damaged, chafed, or corroded wiring in the flexible boot between the door and the body.
A faulty door control module itself, often due to water intrusion or internal circuit failure.
Loose or corroded connector pins at the module or at the body control module end of the CAN bus.
A shorted or open CAN bus wire that affects only the branch to that door module.
Low battery voltage or a weak charging system causing modules to drop offline intermittently.

How to diagnose and fix it

Check all fuses related to the door control module and the body control module, and replace any that are blown.
Inspect the wiring harness in the door jamb boot for broken wires, chafing, or corrosion, and repair as needed.
Disconnect and inspect the electrical connectors at the door module for bent pins, corrosion, or loose fit, then clean and reseat them.
Measure battery voltage and charging system output to rule out low voltage as the cause of intermittent communication loss.
Use a scan tool to check for other codes in the body control module and to perform a network integrity test if available.
If wiring and power are good, substitute a known-good door control module of the same part number to confirm the fault.
After repairs, clear the code and verify that communication is restored and the code does not return after a test drive.

Door module communication faults often misdiagnosed

A door that has been recently repaired or had a window regulator replaced is a prime suspect because the harness in the door boot is easily pinched during reassembly.
Water leaks into the door cavity can corrode the module's circuit board and cause intermittent communication loss long before the module fails completely.
The code can set if the door module's power or ground is interrupted even briefly, so a loose battery terminal or a failing body ground can be the real culprit.
Some vehicles use a separate sub-bus for door modules, and a fault on that sub-bus can set U0203 without affecting the main CAN bus, leading technicians to overlook the sub-bus wiring.
Replacing the door module without checking the harness is a common misdiagnosis; always verify power, ground, and CAN voltage at the module connector before condemning the part.

Can I keep driving with U0203?

You can usually drive the vehicle safely, but the affected door may not lock or unlock properly, which is a security risk, and other functions on that door may be inoperative. Avoid leaving valuables in the car and have the fault diagnosed soon, especially if the door will not latch securely.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.