Network, generic (extended)

U302E Ignition Output On

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U302E applies to an output intended to carry voltage in On alone, which means it has to switch off while the starter turns. The driving module must blank out that intended gap during cranking and judge the output only in steady power modes, otherwise every start would log the code. How such a check can be built is shown in Yazaki's patent CN106797120A: a controller measures the voltage behind a second ignition relay, treats a reading below a threshold set between nominal voltage and 0 V as a relay that failed open, warns the driver on a display and moves the affected loads over to the first ignition feed. Transferred to U302E, a dead output in On points to a relay stuck open, a blown fuse or a broken wire, while voltage in Off points to a welded contact or a driver stuck on. No manufacturer documents U302E publicly.

Likely causes

Run relay not closing, e.g. burnt contacts or open coil
Blown fuse or broken wire behind the relay
Welded contact or driver stuck on, leaving the output live in Off
Module software judging the intended cut during cranking as a fault

Symptoms

  • Loads on the run-only feed dead with the engine running
  • Power supply warning in the cluster
  • Battery discharged when the output stays on after shut-off

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€20–600
Time0.5–3 h

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

Parts involved

ignition outputignition relayoutput wiring

Related codes

U300EU302DU302FU3030P2530

References: patents.google.com, law.cornell.edu.