P0CB9: Sensor P's low circuit voltage becomes an extreme hot reading

P0CB9 concerns hybrid/EV battery temperature sensor P circuit low. The 2018 GM table describes an NTC thermistor with a pull-up resistor. High temperature lowers the sensed voltage, while a short to ground can create the same electrical direction.

An extreme display needs interpretation

The failure threshold is converted temperature above 160 °C. Eight failures out of ten samples at 100-millisecond intervals meet the monitor's criterion. It requires system voltage above 10.2 V and absence of the designated battery-interface communication faults. Reporting is Type B, two trips.

That endpoint belongs to a circuit check. It is not a safe operating limit and does not, by itself, prove that the battery reached the displayed temperature. Conversely, an electrical-code label does not justify ignoring independent evidence of overheating.

Preserve both electrical and thermal context

Record P's signal or converted value, the other temperature measurements and associated warnings. The vehicle-specific diagnostic must determine whether the extreme is credible and identify any sensing-path fault. P0CB9 alone cannot select a replacement sensor or cooling component.

After repair, confirm credible P data and completion of the eligible endpoint monitor. A cleared code alone is not evidence of a sound input. Establish P's actual mapping from the correct vehicle information before physical inspection. Internal battery electrical work requires qualified high-voltage service and the manufacturer's 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 942.