What it means
The control circuit of the belt-integrated starter/generator (BISG) belt tensioner reports a control circuit/open condition. Belt tension cannot be modulated for assist/regen modes.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The belt-integrated starter-generator (BISG) uses a controlled tensioner to manage belt tension during engine starting, electric assist, and regenerative charging. The module monitors the tensioner control circuit and sets this code when it detects an open circuit, so it may be unable to command belt tension for those functions.
Common causes
Most likely first.
- Open in tensioner control wire
- Open tensioner actuator
- Pin pushed back out of connector body
Symptoms
- Check-engine light or hybrid-system warning
- Reduced or unavailable start-stop, assist, or regenerative charging
How to diagnose it
- Record freeze-frame data and scan for related hybrid or charging-system codes to establish when BISG functions were disabled.
- Inspect the tensioner connector for a loose plug, damage, corrosion, or a pin pushed back into the connector body.
- Trace the tensioner control wire for breaks, pulled sections, or damaged insulation between the actuator and its controller.
- Check circuit continuity and connector pin fit with the circuit isolated as directed by the manufacturer's procedure.
- Test the tensioner actuator for an internal open circuit using the manufacturer's specification.
Common fixes
- Reseat the tensioner connector and secure any backed-out pin.
- Repair a broken or disconnected section of tensioner control wiring.
- Clean or repair damaged connector terminals to restore contact.
- Replace the BISG belt tensioner actuator if it tests open.
Can I keep driving?
The vehicle may lose start-stop, electric assist, or regenerative charging, and a hybrid-system warning may appear. Limit demanding driving if power is reduced, and stop if the belt becomes noisy or a charging warning appears.
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.