Chassis, generic

C0727 Trailer Connector Circuit Malfunction

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

C0727 has no public trace in the public J2012 tables, NHTSA bulletins or maker indexes, and trailer faults usually sit in B or U codes. The circuits behind the title are documented. GM trucks with the trailering app have a trailer lighting module that powers the socket with pulse-width signals; in 2019 the park, stop and turn circuits had to draw at least 55 mA before a trailer was recognised, and the module watches for bulb outage and overcurrent. Trailers with their own lighting module can confuse it. Ford traced false trailer connected messages on the 2019-20 Ranger to moisture in the 4-pin and 7-way connectors, and Stellantis advises packing the Ram 2500 bumper socket with dielectric grease against corrosion. Lamps on the trailer then fail or flicker.

Likely causes

Moisture or corrosion in the vehicle trailer socket
Short, LED load too low or own lighting module on the trailer
Damaged vehicle harness or trailer lighting module

Symptoms

  • Trailer lamps inoperative or flickering
  • Trailer connected/disconnected message without reason

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–400
Time0.3–2 h

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

Parts involved

trailer connectortrailer wiringtrailer brake module

Related codes

C0784C0860U0137

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.