Chassis, generic

C0784 Trailer Brake Force Sensor Circuit Malfunction

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Searches for C0784 came up empty: the public code lists, the NHTSA bulletin index, GM's keyword table and the Saab and Mitsubishi indexes all miss it. The title points to the signal an integrated trailer brake controller uses to gauge how hard the driver is braking. Patents show the usual choices: a pressure transducer on the master cylinder, a pedal travel sensor or an accelerometer, whose proportional output sets the current to the trailer's electric brakes. Continental adds a gain optimiser that compares master cylinder pressure with measured deceleration, for example 0.5 g expected at 80 bar, and raises the trailer gain when the rig stops too weakly. Without a valid signal the controller can no longer scale trailer braking to the driver's demand.

Likely causes

Open, shorted or corroded wiring or connector of the brake force or pressure signal
Brake pressure transducer or deceleration sensor defective
Trailer brake controller module faulty or wrongly configured

Symptoms

  • Trailer brakes weak, delayed or not applied when the vehicle brakes
  • Trailer brake warning message in the instrument cluster

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–600
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

trailer brake controllerbrake force sensorsensor wiring

Related codes

C0727C0860

References: patents.google.com, patents.google.com.