What it means
The ECM detects a circuit high fault on the hybrid/ev battery temperature sensor b circuit. Reading cannot be used reliably for control.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Battery temperature sensor B monitors temperature at its location in the hybrid/EV battery pack, and the control module uses that data to manage battery operation. P0AC8 sets when the sensor B circuit signal is above the expected range, so the module cannot rely on the temperature reading.
Common causes
Most likely first.
- Signal wire shorted to B+
- Open sensor
- 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
- Save freeze-frame data and scan for related battery-temperature codes, noting whether the high signal appeared at start-up, during charging, or after driving.
- Compare sensor B live data with other battery temperature sensors and the vehicle's operating conditions to confirm whether the reading is implausibly high or fixed.
- With the vehicle safely powered down according to service information, inspect sensor B's connector and harness for an open circuit, loose pins, corrosion, or a signal wire contacting B+.
- Check the signal circuit for a short to B+ and test connector continuity against the manufacturer's wiring information.
- If the circuit is sound, test sensor B and the control module input using the manufacturer's procedure to distinguish an open sensor from a module fault.
Common fixes
- Repair an open or damaged sensor B signal wire and secure its connector.
- Clean or replace corroded or damaged connector terminals.
- Repair a sensor B signal wire shorted to B+.
- Replace battery temperature sensor B if testing confirms it is open or faulty.
Can I keep driving?
Avoid heavy loads and charging if the hybrid system has reduced power or raised a battery warning. A falsely high temperature reading can cause the vehicle to restrict battery charging or assistance; stop if an actual overheating 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.