What it means
The negative contactor B of the battery charging system reports a stuck closed condition. HV charging path cannot be commanded reliably.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Negative contactor B is a high-voltage switch in the battery charging path. The hybrid control module checks whether the contactor opens when it is commanded to do so; this code sets when feedback indicates that B remains closed.
Common causes
Most likely first.
- Contactor contacts welded closed
- Output driver stuck on
- Carbon or debris buildup preventing free movement
Symptoms
- Hybrid-system warning light or message
- Vehicle may not enter READY mode
- Charging may be unavailable
How to diagnose it
- Record freeze-frame data and check hybrid-system live data for the command and reported state of negative contactor B, since this confirms when the mismatch occurs.
- Check the vehicle's service information for the specified safe diagnostic procedure, and inspect the accessible low-voltage connectors and wiring to contactor B for damage or contamination.
- Use the scan tool's supported output test to command contactor B open and compare the command with its reported state.
- With the high-voltage system made safe according to the manufacturer's procedure, have the contactor and its feedback circuit checked for welded contacts or a stuck output driver.
- Repair the identified fault, then clear the code and verify that contactor B changes state as commanded and the vehicle enters READY normally.
Common fixes
- Repair damaged or contaminated low-voltage wiring or connector terminals for contactor B.
- Clean or restore a connector with contamination that prevents contactor B from moving freely.
- Replace negative contactor B if its contacts are welded or its mechanism is jammed.
- Repair or replace the contactor output driver if it is confirmed to remain energised.
Can I keep driving?
Avoid relying on the vehicle for normal driving or charging; it may refuse READY or have an unreliable high-voltage charging path. Have the hybrid system checked promptly, and do not handle high-voltage components.
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.