U01AC code meaning
Lost Communication With Hybrid/EV Battery Interface Control Module M
Network system Generic code U01xx codes Check engine light
What U01AC means
U01AC belongs to battery interface control module M and is the last one GM mentions: its 2018 hybrid table ends the fault bundle BICM Loss of Comm at U01AC, i.e. thirteen boards, whereas GM's model-specific tables from 2016 to 2019 only monitor A to H. For diagnosis the order of events matters more than the letter. GM first sets the summary code U179C for one or more silent boards and only afterwards names the first board it cannot reach, so a workshop should record all stored module codes, U179C and the invalid-data and software codes of the same letter (U04AD, U0346) before clearing, then compare the count with the boards actually fitted. No manufacturer publishes a threshold or MIL type for M.
U01AC at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1 to 10 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U01AC
- Summary code for missing boards stored together with U01AC
- Battery warning and reduced output
Common causes of U01AC
- Most likelyChain connection between module L and module M interrupted
- PossibleBattery interface control module M defective
- Less likelyController calibration expects more boards than the pack contains
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hv battery interface module mCommunication bus
What each part of U01AC means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| AC | The exact fault in that area. |
What to do next
- Note U01AC 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 U01AC
What does U01AC mean?
U01AC means "Lost Communication With Hybrid/EV Battery Interface Control Module M". U01AC belongs to battery interface control module M and is the last one GM mentions: its 2018 hybrid table ends the fault bundle BICM Loss of Comm at U01AC, i.e. It is a generic code, so it means the same on every make.
Is it safe to drive with U01AC?
Drive gently and only to a workshop. With U01AC the car can go into limp mode (reduced power) to protect itself.
Will U01AC fail an emissions test?
Yes, it can. U01AC is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U01AC to fix?
Difficulty: workshop only. A typical repair takes 1 to 10 hours of work. This is a job for a workshop.
Will U01AC clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.