What it means
The control circuit of the belt-integrated starter/generator (BISG) belt tensioner reports a control circuit low 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 BISG belt tensioner adjusts belt tension so the starter-generator can support starting, assist, and regenerative charging. The module monitors the tensioner control signal and sets this code when that circuit is lower than expected, consistent with a short to ground, a shorted actuator, or poor connector contact.
Common causes
Most likely first.
- Control wire shorted to ground
- Internal short in actuator
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light or hybrid-system warning
- Reduced or unavailable start-stop, assist, or regenerative charging
How to diagnose it
- Review freeze-frame data and related hybrid-system codes to see when assist or regenerative charging was affected.
- Inspect the tensioner connector and terminals for corrosion, looseness, or moisture that could raise contact resistance.
- Check the tensioner control wire for chafing or a short to ground along its route.
- Measure the control circuit for a low signal and check continuity with the actuator disconnected, following the manufacturer's procedure.
- Test the tensioner actuator for an internal short using the manufacturer's specification.
Common fixes
- Clean and secure corroded or loose tensioner connector terminals.
- Repair control wiring shorted to ground.
- Replace the BISG tensioner actuator if testing confirms an internal short.
- Repair damaged connector pins or wiring that is causing high contact resistance.
Can I keep driving?
Start-stop, assist, or regenerative charging may be reduced or unavailable. Avoid relying on electric assist for demanding driving, and stop if the belt slips, 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.