Network, generic (extended)

U302D Ignition Output On/Start

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U302D concerns the output that powers the On/Start circuits, i.e. everything that has to work with the engine running and through cranking but not in Off or Accessory. On GM's 2012 pickups the body control module handles this by switching the coil of the run/crank relay over circuit 5199. GM bulletin PIT5817A, covering 2020–2021 models such as Escalade, Tahoe, Corvette and CT5, shows what goes wrong on that side: the BCM keeps driving ignition main relay KR73 after shut-off, circuit 5199 stays live and the battery runs down, while engine, transmission and brake controllers store P2535 and the cluster stores U300D; the repair is a new BCM. GM records that case through input codes in the receivers, not as U302D. A module that checks its own on/start output would catch the same fault at the source. No manufacturer documents U302D publicly.

Likely causes

Relay driver in the body control module staying on after shut-off
Ignition main relay contact welded or relay not pulling in
Relay coil control wire open or shorted to voltage
Retrofitted device feeding voltage back into the run/crank circuit

Symptoms

  • Battery repeatedly flat, often after a remote start
  • Engine lamp at start-up with P2535 stored in engine and transmission modules
  • No start or modules without power if the output fails open

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€20–900
Time0.5–3 h

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

Parts involved

ignition outputignition relaybody control moduleoutput wiring

Related codes

U300DP2535U302EU3030U3023

References: static.nhtsa.gov, gmupfitter.com, law.cornell.edu.