P0AC8: Hybrid/EV Battery Temperature Sensor B Circuit High

P0AC8 reports that battery temperature sensor B delivers a voltage above its valid range, which for an NTC thermistor reads as extreme cold. An open wire, a disconnected sensing board plug or a broken sensor are typical. GM's 2016 and 2019 tables set it below -69 °C in 8 of 10 samples, the two-mode hybrid tables of 2011 and 2013 below -45 °C in 30 of 40, and GM's 2013 table 13OBDG05C above 4.63 V, about -45 °C, in 7 of 10; all Type B, two trips. In the Chevrolet Volt, bulletin 18-NA-342 links such codes to a Battery Too Cold message above -25 °C ambient and prescribes reprogramming. A pack believed to be frozen gets strict charge and power limits.

High severity. Can I keep driving?If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

Symptoms

Check engine or hybrid warning light
Battery too cold message although it is not cold
Strongly reduced charging and electric power

Most likely causes

Open signal or return wire of sensor B
Thermistor open internally
Controller software issue on the Volt (bulletin 18-NA-342)
Signal shorted to the reference voltage

What to check, in order

Start with the simplest. You can tick off each step.

Read the codes with a hybrid-compatible scanner and write down the freeze frame data
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Make sure the battery cooling air intake is clean
Check the 12 V auxiliary battery, which can also trigger warnings
Leave any high-voltage measurements to a specialized repair shop

Good to know

It can trigger limp mode.
It affects emissions.

What each character of P0AC8 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
A: Hybrid or air and fuel
C8: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0AC8?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0AC8?

The most common causes are: open signal or return wire of sensor B; thermistor open internally; controller software issue on the Volt (bulletin 18-NA-342).

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.