U0D90
Lost Communication With Trailer Brake Control ModuleU0D90 is a generic OBD-II network diagnostic trouble code: Lost Communication With Trailer Brake Control Module. It is logged by the engine control unit when the network monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What U0D90 means
U0D90 is set when the towing or chassis control module loses network communication with the trailer brake control module. The trailer brake control module governs integrated trailer brake output signals and monitors trailer brake status during towing operations. When communication is lost, the towing system cannot coordinate trailer brake application with the vehicle braking system, which is a safety concern when towing.
This code is most often triggered when the trailer brake module loses power or ground, when the CAN network branch serving the trailer brake module is damaged, or when the module itself has failed. On vehicles where the trailer brake module is located in an exposed area near the rear hitch, connector corrosion from road moisture is a frequent cause. The code may also set when the module is not installed on a vehicle equipped with the wiring harness but no module fitted.
Diagnosis should confirm whether a trailer brake module is installed and is expected to communicate on this network. If it is present, power supply and connector integrity should be verified first. If the module is not installed (optional equipment), the code may reflect a network configuration mismatch that can be resolved through module programming or feature deactivation.
Common causes
Most-frequently reported root causes when U0D90 is logged.
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1
Loss of battery power or ground to the trailer brake control module.
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2
Open or shorted CAN bus wiring to the trailer brake module, often at the rear of the vehicle.
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3
Corroded or water-damaged connector at the trailer brake module or hitch wiring.
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4
Failed trailer brake control module no longer transmitting on the bus.
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5
Trailer brake module not installed but expected by the vehicle network configuration.
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6
CAN bus wiring damage from hitch work, receiver installation, or trailer coupling impacts.
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7
Loose or poorly seated module due to vibration from towing cycles.
Symptoms drivers notice
How to diagnose U0D90
A typical diagnostic flow when this code is present.
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1
Retrieve all DTCs from all modules; note whether the trailer brake module is listed in the network device scan.
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2
Confirm whether a trailer brake module is physically installed; if not, check whether the vehicle network configuration expects one.
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3
Verify power supply voltage and ground continuity at the trailer brake module connector.
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4
Inspect the module connector and wiring for corrosion, moisture intrusion, or physical damage near the hitch area.
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5
Measure CAN bus differential voltage at the module connector with the ignition on to verify bus signal integrity.
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6
Attempt direct module communication via scan tool; failure to communicate after confirming power and bus signal points to a failed module.
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7
Replace or install the module as appropriate and retest; reprogram if required by the manufacturer.
Related network codes
- U0D88 — Lost Communication With Battery Energy Control Module 'D'
- U0D8B — Lost Communication With Battery Energy Control Module 'G'
- U0D8C — Lost Communication With Battery Energy Control Module 'H'
- U0D8D — Lost Communication With Battery Energy Control Module 'I'
- U0D8E — Lost Communication With Suspension Control Module
- U0D92 — Lost Communication With Auxiliary Heater Control Module
Frequently asked questions
Can U0D90 set even when not towing a trailer?
Yes. The trailer brake control module is a permanently installed ECU on vehicles equipped with integrated trailer brake control and must communicate on the network regardless of whether a trailer is attached.
Is this code serious if I never tow?
If the vehicle is not used for towing it does not create an immediate safety risk, but the MIL will remain on and the network fault should be investigated to prevent other modules from misinterpreting the missing data.
Could aftermarket trailer wiring cause U0D90?
Aftermarket 4-pin or 7-pin trailer adapters that tap into the chassis harness can introduce shorts or corrosion that affect the module or its wiring. Inspect the hitch wiring area if aftermarket trailer electrics have been fitted.
Do all vehicles with a tow hitch have a trailer brake module?
No. Basic tow packages often include only a wiring harness for trailer lights. Integrated trailer brake control modules are typically found on trucks and SUVs with a factory trailer brake prep package.
Disabling U0D90 in software
RaceTune can permanently disable U0D90 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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