What it means
The battery pack cooling fan enable circuit signal is above the expected range. The code does not identify a particular wiring-damage pattern or test procedure.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The battery pack cooling fan enable circuit carries the signal used by the control module to enable battery cooling fan operation. P0D66 sets when that signal is above its expected range, so the module may see the fan as enabled when it should not be.
Common causes
Most likely first.
- Wire shorted to B+
- Pull-down resistor open
- 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 related fan codes to identify the conditions when the high enable signal was detected.
- Check live enable command and fan status, if available, for a signal that remains high when the system is not requesting cooling.
- Inspect enable-circuit wiring for contact with battery positive and check connector terminals for corrosion or damage.
- Test the circuit for a short to power and check the pull-down path and connector resistance using the manufacturer's procedure.
- If wiring is intact, test the enable switch and control-module input using vehicle-specific service information.
Common fixes
- Clean or secure corroded or loose enable-circuit terminals.
- Repair a wire shorted to battery positive or other damaged enable wiring.
- Repair or replace a confirmed open pull-down path.
- Repair the control-module input circuit only if testing confirms a fault.
Can I keep driving?
Keep driving limited and avoid high loads or hot conditions, since incorrect fan-enable reporting can interfere with battery cooling and lead to power or charging limits. Stop safely if a battery warning or reduced-power mode 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.