P0CAA: Hybrid/EV Battery Temperature Sensor M Circuit Low

P0CAA means the voltage at sensor M has dropped below its valid band. Sensor M is an NTC element supplied via a bias resistor on the board, so a grounded lead or a shorted element drags the voltage down and reads as an extremely hot spot. GM's 2018 HPC2 table 18OBDG02 fails the test once the converted temperature exceeds 160 °C in 8 of 10 readings taken every 100 ms, Type B, with more than 10.2 V supply. The 2011 Volt table set it above 87.5 °C, a raw count below 680, held for 1.4 s within 2 s over two trips. Mitsubishi's Outlander PHEV calls it a short of sensor [12]: below 0.12 V, roughly above 125 °C, for 2 s; the remedy there is a new battery module or cell monitoring unit. A real overheating shows as P0A7E instead.

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

Warning lamp with strongly reduced battery power
Battery cooling running without reason

Most likely causes

Sensor M signal shorted to ground inside the pack
Thermistor M internally shorted
Measuring input of the cell monitoring unit defective

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
With the connector unplugged, check whether the signal wire is making contact with ground.
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 P0CAA means

P: Powertrain: engine and transmission
0: Generic code: same on every make
C: Subsystem depends on the code range
AA: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0CAA?

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 P0CAA?

The most common causes are: sensor M signal shorted to ground inside the pack; thermistor M internally shorted; measuring input of the cell monitoring unit defective.

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.