What it means
The HV battery pack cooling fan 1 sense circuit reports a sense circuit low fault. Fan speed feedback is unreliable.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The hybrid battery cooling fan circulates air through the high-voltage battery pack, and its sense circuit reports fan 1 speed to the control module. P0BC9 sets when the fan 1 feedback signal is lower than expected, which can result from a signal wire shorted to ground, an internally shorted tachometer, or a poor connector contact.
Common causes
Most likely first.
- Sense wire shorted to ground
- Tachometer internal short
- Connector pins corroded - high contact resistance
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
- Record freeze-frame data and compare commanded fan 1 operation with live speed feedback, if available, to see whether the signal stays low when the fan is commanded.
- With the vehicle powered down as specified by service information, inspect the fan 1 connector and harness for corrosion, damaged insulation, or a signal wire contacting ground.
- Check that the connector terminals are clean, seated, and secure, since poor contact can pull down the feedback signal.
- Use the manufacturer's wiring information to test the fan 1 sense wire for a short to ground and verify circuit continuity.
- If the wiring and connector pass, test the fan tachometer output against the manufacturer's specification for an internal short or failure.
Common fixes
- Clean and properly seat corroded or loose fan 1 sense terminals.
- Repair the fan 1 sense wire where it is shorted to ground.
- Replace the fan assembly if its tachometer fails the specified test.
- Clear the code and confirm fan 1 feedback changes appropriately when commanded.
Can I keep driving?
Avoid heavy driving and charging, which add heat to the battery, and stop if power is limited or an urgent hybrid warning appears. Low or unreliable fan feedback can prompt protective limits and may leave the pack with less cooling.
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.