U0340 code meaning
Software Incompatibility With Hybrid/EV Battery Interface Control Module G
What U0340 means
G is the seventh board, a position GM's 2016–2019 plug-in hybrids really have: table 16OBDG02 describes eight interface modules on a UART daisy chain to the battery system module. That table publishes lost-contact and processor tests for every board, yet it holds no counterpart to the P1EB1 version check of the older VITM design and no U0340. For G, GM thus documents silence (U01A6), not a software conflict. The older four-board design is stricter: P1F06 to P1F09 make each slave return a key value computed by a seed-and-key algorithm and fail it when wrong values persist for 1 s within a 1.4 s window, Type B in the 2015 table. U04A7 is the invalid-data code for G.
U0340 at a glance
- Check engine lightUsually not
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0340
- Hybrid warning, MIL possible depending on the maker
- Electric mode limited or unavailable
- Other battery diagnostics paused while the code is active
Common causes of U0340
- Most likelySeventh board replaced by a unit with another software level
- PossibleBattery system module reflashed without the boards being brought along
- Less likelyDisturbed daisy-chain link garbles the version data of board G
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 g
What each part of U0340 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 40 | The exact fault in that area. |
What to do next
- Note U0340 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 U0340
What does U0340 mean?
U0340 means "Software Incompatibility With Hybrid/EV Battery Interface Control Module G". G is the seventh board, a position GM's 2016–2019 plug-in hybrids really have: table 16OBDG02 describes eight interface modules on a UART daisy chain to the battery system module. It is a generic code, so it means the same on every make.
Is it safe to drive with U0340?
Drive gently and only to a workshop. With U0340 the car can go into limp mode (reduced power) to protect itself.
Will U0340 fail an emissions test?
Yes, it can. U0340 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 U0340 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U0340 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.