U0137

Code

Generic U — Network/User

Lost Communication With Trailer Brake Control Module

Brand: Generic

Type: U — Network/User

Views: UK: 28 EN: 49 RU: 44

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Trailer brake control module has lost power or ground
Damaged, corroded, or disconnected connector at the TBCM
Faulty wiring or open/short in the communication bus (CAN/LIN) to the TBCM
Missing or bad bus termination or wrong bus baud rate
Blown fuse or faulty relay supplying the TBCM
Faulty TBCM (internal failure)

Symptoms

Trailer brake function disabled or inoperative
Trailer-related warning light or message on dash
Loss of other trailer-related features (e.g., trailer tow stability)
Intermittent or permanent fault codes stored in vehicle network
No response from TBCM when interrogated with a scan tool

What to check

Verify the exact DTC and freeze frame data with a capable scan tool
Check if the trailer is connected — inspect trailer connector for corrosion or bent pins
Inspect fuses and relays that supply the trailer brake module
Visually inspect TBCM connector and harness for damage, corrosion, or moisture
Check battery voltage and key-on power at module power pins
Verify good ground(s) at the module chassis ground point

Signal parameters

CAN bus idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (common-mode)
CAN bus dominant: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V)
Typical CAN bus termination resistance (two 120 Ω resistors in parallel) ≈ 60 Ω across CAN_H and CAN_L
Expected wake/standby state: module may be asleep until key on or trailer connected — verify expected behavior per vehicle
Typical bus baud rates: 250 kbps or 500 kbps (verify vehicle spec)

Diagnostic algorithm

Record the DTC(s) and freeze frame. Note operating conditions (key on, engine on, trailer connected).
Visually inspect the trailer connector and harness at the hitch for corrosion, broken wires, or water intrusion. Repair as needed.
Verify fuses and relays feeding the trailer brake module. Replace any blown fuses and re-test.
With key on, measure power and ground at the TBCM connector. Confirm proper battery voltage (approx. 12 V) on power pins and low resistance to chassis on ground pins.
Check for presence of CAN_H and CAN_L signals at the module with an oscilloscope or high-speed multimeter. Verify recessive voltages ~2.5 V and proper differential when active.
Measure termination resistance across CAN_H and CAN_L with power off; expect ~60 Ω. If open or very low, trace and repair wiring/terminators.
Use a scan tool to send requests to the TBCM. If no response, wiggle test harness to look for intermittent connection. Inspect for damaged pins.
Inspect for other modules reporting bus-off or communication faults (e.g., U0100, U0121). Diagnose upstream bus faults first.
If wiring, power, and termination are good but module is still unresponsive, attempt re-initialization or reprogram/reflash per manufacturer procedures if available.
If module remains non-communicative after software attempts and wiring verified, consider replacing the TBCM. Follow vehicle-specific setup, pairing, and coding procedures after replacement.
Clear codes and road test with and without trailer connected to confirm repair. Monitor for recurrence.

Likely causes

Corroded connector or pin at the trailer brake module
Open or shorted CAN bus segment near the trailer connector or module
No key-switched power to the TBCM (fuse/relay issue)
Module software fault or module has entered a bus-off state
Damaged harness near hitch or trailer connector

Fault status

⚠️ Status

Lost Communication With Trailer Brake Control Module — module not responding on vehicle communication bus (CAN/LIN), trailer brake functions may be unavailable.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours

Repair manuals