Network, generic (extended)

U302F Ignition Output Accessory

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U302F is logged by the module that switches the accessory feed for audio, sockets or windows when that feed is out of step with its own command. Two normal behaviours have to be ruled out first. Keyless systems cut accessory power during cranking: in Tokai Rika's patent US7254466B2 the power supply unit releases the accessory relay when start is requested and re-energizes it only once the engine controller reports that combustion has begun. GM's 2012 pickups, on the other hand, keep accessory voltage on after key-off through a relay inside the BCM for roughly 10 minutes, unless a door is opened. Outside those windows, a live feed in a locked car suggests a welded relay or a driver stuck on, and a dead feed in accessory an open relay, fuse or wire. No manufacturer documents U302F publicly.

Likely causes

Accessory relay welded or its driver stuck on
Accessory relay not pulling in
Blown accessory fuse or open feed wire
Retrofitted equipment overloading or backfeeding the accessory feed

Symptoms

  • Radio, sockets or windows dead in accessory mode
  • Accessories still on long after locking, battery drained

Repair estimate

DifficultyEasyDIY possible
Parts and labour€10–500
Time0.3–2.5 h

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

Parts involved

ignition outputignition relayoutput wiring

Related codes

U300FU3032U302BU302EU3030

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