P0CA9: Hybrid/EV Battery Temperature Sensor M Circuit Range/Performance

What does P0CA9 mean?

P0CA9 reports that sensor M stays within its electrical limits yet disagrees with what the remaining pack sensors measure. GM's 2012 Volt table 12OBDG01A only runs the comparison once drive system, plug-in charging and battery conditioning have rested for over 21,600 s; a spread above 25.3 °C from the mean in 50 of 67 samples is a Type B failure. The 2018 HPC2 table 18OBDG02 uses 25.00 °C at 25 ms sampling and is suspended whenever circuit faults of the sensors or a communication loss with the battery interface module exist. Mitsubishi uses P0CA9 for module sensor [12] of the Outlander PHEV: after more than 3,600 s soak and at pack temperatures from −30 to 60 °C, a deviation of 13 °C or more from the mean of all 50 sensors for 0.32 s sets it. Drift or a loose sensor is typical.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Warning lamp appearing after a long parking period
• Battery power limited

Common causes

• High Thermistor M drifting while staying in its electrical range
• Medium Sensor M lost thermal contact with its module
• Low Module section genuinely warmer or colder, e.g. cooling fault or weak cell

Likelihood is a general estimate across vehicles; your make and model may differ.