Network, generic (extended)

U302C Ignition Output Off/On/Start

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U302C covers an ignition output that encodes several states on one wire: Off, On and Start each get their own level, so a single conductor passes the power mode on to other units. It is the sending counterpart of coded inputs like the Off/Run/Crank circuit that GM's wiring manual for its 2012 light-duty trucks shows between ignition switch and body controller, which uses separate levels for key removed, key in at off, running and cranking. A module producing such a coded line stores U302C once the level read back at its own pin differs from the state it means to transmit. No manufacturer documents U302C publicly. Since receivers evaluate voltage bands rather than on or off, a partial short, an extra load or a corroded pin can turn run into start or off without the line going dead, so measure it in each mode with receivers connected.

Likely causes

Corroded or loose pin shifting the coded level
Faulty input in a receiving module pulling the line out of its band
Chafed wire with a partial short to ground or voltage
Faulty output stage in the sending module

Symptoms

  • Other modules acting on a wrong power mode, e.g. shutting down or not waking
  • Sporadic warnings that change with key position or button presses

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€30–600
Time0.5–3 h

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

Parts involved

ignition outputoutput wiring

Related codes

U300CU302BU302DU3031U3011

References: law.cornell.edu, gmupfitter.com.