Powertrain, generic · Hybrid propulsion

P0C99 Hybrid/EV Battery Temperature Sensor L Circuit Low

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modePossible

P0C99 reports a sensor L voltage below the valid range. Because the thermistor works against a bias resistor on its monitoring board, any ground fault or an internally shorted sensor drags the voltage down, which reads as a very hot module. GM's 2019 HPC2 table 19OBDG02 flags it once the converted value exceeds 160 °C in 8 out of 10 readings at 100 ms intervals; it is a Type B code and needs supply above 10.2 V. The 2012 Volt table groups L with the other sensors and passes them only at or below 87.5 °C, which equals a raw count of 680 or more, and needs 1.4 s out of 2 s to fail. Mitsubishi does not use L codes. If the pack is really overheating, P0A7E appears instead. Expect a warning lamp and reduced battery power.

Likely causes

Sensor L signal shorted to ground

Thermistor L shorted internally

Monitoring board channel pulling the input low

Symptoms

Warning lamp and reduced battery power
Battery cooling running for no apparent reason

Repair estimate

DifficultyShop_onlyWorkshop job

Parts and labour€150–2,500

Time1–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hv battery temp sensor lwiring harnessbms

References: gsi.ext.gm.com, gsi.ext.gm.com.