U3021 code meaning
Control Module Wake-up Circuit B Performance
What U3021 means
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.
U3021 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U3021
- Warning lamp or message after a wake event, e.g. after charging
- Function works, but the code returns sporadically
Common causes of U3021
- Most likelySoftware in sender or receiver judging the wake timing wrongly
- PossibleSource on line B raising or dropping its signal late
- Less likelyContact resistance on line B slowing the level change
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Wakeup circuit bWakeup wiring
What each part of U3021 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 21 | The exact fault in that area. |
What to do next
- Note U3021 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U3021
What does U3021 mean?
U3021 means "Control Module Wake-up Circuit B Performance". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with U3021?
U3021 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U3021 fail an emissions test?
U3021 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U3021 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 2 hours of work. This is a job for a workshop.
Will U3021 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.