What it means
The BMS detects a circuit fault on voltage sense channel U of the high-voltage battery. Cell-group voltage measurement is unreliable on this channel.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The BMS reads a cell group's voltage through channel U, a separate sense path in the high-voltage battery. This code indicates a general electrical fault on channel U, such as an open or short, so the BMS cannot trust that group's voltage reading.
Common causes
Most likely first.
- Open or short in the voltage-sense wiring
- Loose, corroded, or damaged connection
- Battery monitoring module fault
Symptoms
- EV/hybrid system warning light on
- Reduced power output or limp mode
- Charging may fail or be slowed
- Reduced electric range
How to diagnose it
- Save freeze-frame data and compare channel U's reported voltage with adjacent cell-group readings to identify whether the signal is absent, implausible, or changing.
- With the vehicle powered down under the manufacturer's high-voltage safety procedure, inspect the accessible channel U connector and harness for damage, looseness, or corrosion.
- Check channel U connector pins and seating, since a poor connection can create the same general circuit fault as damaged wiring.
- Have a qualified hybrid technician test channel U wiring for continuity and shorts using the manufacturer's procedure.
- If the wiring passes, test the battery monitoring module's channel U input and related connections to determine whether the module is at fault.
Common fixes
- Reseat a loose channel U connector.
- Clean or repair corroded or damaged channel U connector pins.
- Repair or replace channel U wiring that is open or shorted.
- Replace the battery monitoring module only if its channel U input fails the manufacturer's tests.
Can I keep driving?
Keep trips short and avoid hard acceleration if the vehicle has reduced power; charging may be restricted and electric range may fall. Stop if a battery safety warning appears, and arrange prompt diagnosis by a technician qualified to work on hybrid or EV systems.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.