U04A2 code meaning
Invalid Data Received From Hybrid/EV Battery Interface Control Module B
Network system Generic code U04xx codes Check engine light
What U04A2 means
U04A2 covers the second interface board of the high-voltage pack, module B: its frames reach the battery controller but carry implausible content. No manufacturer documents this exact code publicly. The closest published logic is GM's 2016 hybrid table 16OBDG02, where the battery systems module talks to eight interface boards, A to H, over a serial UART daisy chain. If no data at all arrive from B for 5 s at more than 10.2 V, GM logs the lost-link sibling U01A1 as Type A, after first trying a loop-back test that bypasses the chain. U04A2 is the opposite case: the link exists, the content fails. CARB lists battery voltage sensors among the hybrid storage inputs that OBD has to check. Software issues fall under U033B.
U04A2 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1 to 8 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U04A2
- Hybrid or EV system warning, MIL on plug-in hybrids
- Electric range or power reduced
Common causes of U04A2
- PossiblePoor contact in the chain connection between interface boards A, B and C
- PossibleInterface control module B internally faulty
- PossibleOutdated calibration in the battery controller
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 b
What each part of U04A2 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| A2 | The exact fault in that area. |
What to do next
- Note U04A2 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 U04A2
What does U04A2 mean?
U04A2 means "Invalid Data Received From Hybrid/EV Battery Interface Control Module B". U04A2 covers the second interface board of the high-voltage pack, module B: its frames reach the battery controller but carry implausible content. It is a generic code, so it means the same on every make.
Is it safe to drive with U04A2?
Drive gently and only to a workshop. With U04A2 the car can go into limp mode (reduced power) to protect itself.
Will U04A2 fail an emissions test?
Yes, it can. U04A2 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 U04A2 to fix?
Difficulty: workshop only. A typical repair takes 1 to 8 hours of work. This is a job for a workshop.
Will U04A2 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.