P0C46: Battery coolant sensor A changes erratically

P0C46 is hybrid/EV battery pack coolant temperature sensor A circuit intermittent/erratic. The 2018 GM HPC2/VICM table evaluates accumulated movement in the coolant temperature signal rather than comparing it with a single overtemperature limit.

“String length” measures variation

The monitor sums absolute differences over ten consecutive samples and lists a threshold above 64 °C. That number represents total signal variation, not a rule that the coolant itself must be hotter than 64 °C. Opposite-direction changes both add to the result.

The table requires system voltage above 10.2 V and absence of P0C44, P0C45 and U185A for the relevant sensor status. It lists four failures out of five evaluations at 100-millisecond sampling and Type B, two-trip reporting. The difference formula refers separately to a reading 250 milliseconds earlier; those timings should not be collapsed into an invented drive-cycle duration.

Preserve a trace rather than one temperature

A value that looks normal after the event can conceal a prior jump-and-return pattern. Compare the trace with circuit-range and communication fault status before concluding that cooling flow failed. P0C46 alone does not identify a bad pump or prove actual coolant overheating.

Use the correct vehicle's coolant-sensor diagnostic and confirm a stable credible signal through an eligible test after repair. Work involving hybrid battery cooling access requires the applicable professional safety procedure.

Source and applicability

This explanation follows the documented GM monitor, not a verified application to every vehicle with this code. Confirm the vehicle, reporting module and calibration in current service information. GM diagnostic table, physical page 981.