U01AB code meaning
Lost Communication With Hybrid/EV Battery Interface Control Module L
Network system Generic code U01xx codes Check engine light
What U01AB means
U01AB points at battery interface control module L, the twelfth position. The link to such a board has to bridge a large voltage offset, because the lowest and highest boards of a stack sit hundreds of volts apart. NXP's MC33771C, as one example, talks over a two-wire twisted pair coupled through transformers or capacitors at up to 2 Mbit/s, and Wikipedia's battery management article mentions optical isolation and radio as the alternatives. A broken coupling element or a damaged twisted pair at L can therefore cut the board off while it still measures correctly. No vehicle maker documents U01AB with a threshold of its own; GM lists it only in the 2018 fault bundle BICM Loss of Comm, so how the MIL behaves depends on the individual system.
U01AB at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1.5 to 10 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U01AB
- Battery or hybrid warning
- Power limited, charging may be blocked
Common causes of U01AB
- Most likelyTwisted-pair chain line to module L chafed, pinched or unplugged
- PossibleIsolating transformer or capacitor on the link to L failed
- Less likelyBattery interface control module L defective
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 lCommunication bus
What each part of U01AB means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| AB | The exact fault in that area. |
What to do next
- Note U01AB 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 U01AB
What does U01AB mean?
U01AB means "Lost Communication With Hybrid/EV Battery Interface Control Module L". U01AB points at battery interface control module L, the twelfth position. It is a generic code, so it means the same on every make.
Is it safe to drive with U01AB?
Drive gently and only to a workshop. With U01AB the car can go into limp mode (reduced power) to protect itself.
Will U01AB fail an emissions test?
Yes, it can. U01AB 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 U01AB to fix?
Difficulty: workshop only. A typical repair takes 1.5 to 10 hours of work. This is a job for a workshop.
Will U01AB clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.