P0C90: Sensor J circuit high can produce an implausibly cold reading

P0C90 identifies hybrid/EV battery temperature sensor J circuit high. The 2018 GM table describes an NTC thermistor with a sensing-board pull-up resistor. A cold sensor or an open circuit moves the sensed voltage upward, which converts to a lower temperature value.

The endpoint being monitored

The listed failure threshold is a converted reading below −69 °C. Eight failed samples out of ten at 100-millisecond intervals satisfy this implementation's evaluation. System voltage must exceed 10.2 V, with no active battery-interface communication fault in the defined group. GM lists Type B, two trips.

“Circuit high” consequently does not mean the battery is hot. An extreme cold report may be electrical evidence, and the code does not establish the actual pack temperature by itself.

Preserve the disagreement with reality

Compare J's value with the other temperature information and the event conditions. A plausible value from another channel does not repair J, but it provides context for the vehicle-specific circuit investigation. The source identifies an open circuit as one possible mechanism, not a guaranteed location or failed part.

After the appropriate repair, confirm credible J data while the circuit diagnostic runs. Reconnecting scan equipment or clearing memory alone cannot establish that result. Sensor J's physical mapping and test procedure must come from the actual vehicle information; internal battery work requires trained high-voltage personnel.

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 919.