What it means
The HV battery temperature sensor M reports a circuit low fault. Cell-group temperature monitoring impaired on this channel.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Sensor M measures temperature at its assigned area of the high-voltage battery, and the hybrid or EV control module uses that reading to manage battery protection, power, and charging. This code sets when the M sensor signal is lower than the module expects, which can happen if the signal is shorted to ground or the sensor is internally shorted.
Common causes
Most likely first.
- Signal wire shorted to ground
- Internal sensor 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
- Use a scan tool to save freeze-frame data and compare Sensor M's reported temperature with other battery temperature readings; an implausibly low or fixed value helps confirm the affected channel.
- With the vehicle powered down according to the manufacturer's procedure, inspect Sensor M's connector and accessible wiring for corrosion, damage, or a signal wire contacting ground.
- Check whether the Sensor M connector pins are corroded or damaged, since poor contact can distort the low signal.
- Test the Sensor M signal circuit for a short to ground and check the sensor itself using the manufacturer's procedure.
- If the wiring and sensor pass, verify the module's Sensor M input and related connections using the manufacturer's diagnostic procedure.
Common fixes
- Clean or repair corroded Sensor M connector pins and ensure the connector is fully seated.
- Repair damaged wiring or insulation that lets the Sensor M signal short to ground.
- Replace the Sensor M temperature sensor if it fails testing.
- Repair the module connection or replace the control module only if diagnosis confirms its input is faulty.
Can I keep driving?
Avoid relying on electric power or charging performance while the battery temperature reading is unreliable; the vehicle may limit output or charging to protect the high-voltage pack. If power is substantially reduced or a hybrid/EV warning calls for stopping, follow the vehicle's instructions and arrange service.
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.