Network, generic (extended)

U3021 Control Module Wake-up Circuit B Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U3021 is the plausibility code for wake-up line B: the wire is neither open nor shorted, but the wake signal arrives at the wrong time or does not match what other inputs say. No manufacturer documents U3021 publicly. The closest published logic is Ford's U301D for line A in the 2019 Fusion Energi battery module, which fails when the charge wake-up is still low although the charger output voltage is already in the window for closing the contactors. Chrysler's powertrain counterpart P06E4, wake-up circuit performance, appears in 2024 Jeep Wrangler 4xe bulletins (e.g. 21-017-24) that cure it with new module software. Both cases point the same way: a performance fault on a wake line is often a timing question between two modules and is more often solved by a software update than by new wiring.

Likely causes

Software in sender or receiver judging the wake timing wrongly
Source on line B raising or dropping its signal late
Contact resistance on line B slowing the level change

Symptoms

  • Warning lamp or message after a wake event, e.g. after charging
  • Function works, but the code returns sporadically

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€0–400
Time0.5–2 h

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

Parts involved

wakeup circuit bwakeup wiring

Related codes

U301DU301EU301FU3020P06E4

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