Network, generic (extended)

U300D Ignition Input On/Start

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U300D concerns the line that should be live in On and Start only, which GM calls Run/Crank Ignition 1; in GM's 2012 truck wiring manual it is active in run and crank and inactive in off and accessory. A module sets the code when this line and the power mode on the bus disagree. GM's PIT5817A for 2020–2021 Envision, CT4, CT5, Escalade, Corvette, Tahoe, Suburban and Yukon shows the typical case: the instrument cluster stores U300D while the ECM, TCM and brake module log P2535, often after remote start, and the customer finds a dead battery and a service engine lamp. The BCM's driver for the ignition main relay stays on after key-off and keeps circuit 5199 powered, so the line remains live with the car off; the fix is a new BCM. The cluster's code itself is the witness, not the cause.

Likely causes

Body control module keeping the run/crank relay energized after key-off
Run/crank relay sticking closed or failing to close
Blown fuse or open wire in the run/crank feed to the module
Backfeed from an aftermarket device tapped into the run/crank circuit

Symptoms

  • Battery repeatedly discharged after the car was parked
  • Service engine lamp at start-up with P2535 in other modules
  • Cluster or other modules staying awake with the ignition off

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 inputignition relaybody control moduleignition wiring

Related codes

P2535P2534U300EU3023U300C

References: static.nhtsa.gov, gmupfitter.com.