What it means
A control module has stopped receiving expected messages from the trailer brake control module. Trailer brake control or related trailer functions may be limited or unavailable.
How it works
The trailer brake control module communicates with vehicle modules to coordinate trailer braking functions. U0137 sets when expected messages from that module are missing, so trailer brake control or related trailer features may not work.
Common causes
Most likely first.
- Trailer brake control module power or ground fault
- Damaged network wiring or connector
- Trailer brake control module failure
- Low system voltage
Symptoms
- Trailer brake warning or message
- Trailer brake control may be unavailable
- Other communication codes
How to diagnose it
- Scan all modules and review freeze-frame data for U0137 and any low-voltage or network faults.
- Check battery and charging-system condition, then confirm whether the fault occurs with a trailer connected, if applicable.
- Inspect the trailer brake control module connector and harness for corrosion, water, loose pins, or damage, including trailer-side connections if the fault is connection-dependent.
- Check the module's power and ground circuits under load against the manufacturer's specification.
- Test network wiring to the trailer brake control module for opens, shorts, or poor connections using the manufacturer's procedure.
- If power, ground, and network wiring are sound, check module communication with a scan tool before considering replacement or configuration.
Common fixes
- Restore battery or charging-system performance if voltage is low.
- Clean and secure the trailer brake module or trailer connector if corrosion or a loose connection is found.
- Repair damaged trailer brake module wiring or network connections.
- Restore the module's power or ground supply.
- Replace and configure the trailer brake control module if it remains unresponsive with sound circuits.
Can I keep driving?
Do not tow a trailer until you confirm its brakes work correctly; use the vehicle without a trailer only if it drives and brakes normally. Trailer braking may be reduced or unavailable, increasing stopping distance and risk of trailer sway.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.