P205C: low tank-temperature signal can represent an electrically hot reading

P205C is a circuit-low fault for the reductant tank-temperature sensor. The reviewed GM source describes a thermistor arrangement in which lower signal voltage corresponds to higher represented temperature. “Low” therefore refers to the electrical signal, not to cold reductant.

Reading the threshold correctly

The malfunction boundary is below 0.3 volt, with 75°C shown as the corresponding temperature reference. The strategy describes detection of a short-to-ground or open-circuit condition. That source-specific inclusion of an open circuit should not be replaced by assumptions from a different thermistor circuit design.

A displayed hot tank temperature during the fault may be the consequence of the electrical transfer relationship. It is not independent proof that the fluid actually reached that temperature. The voltage validity question should be resolved before interpreting the temperature as a thermal event.

Conditions and verification

The vehicle must be in an active power mode, which includes accessory, run, start request or propulsion. Specified controller-internal faults must be absent. The diagnostic requires 50 failing samples at 0.01 second each, described as 0.5 second, and lists Type A reporting over one trip.

Verification should establish that the low-voltage monitor completes with a valid sensor signal, then assess whether the reported temperature is credible. The source does not provide a connector pinout, resistance chart or component-replacement verdict. Its threshold and electrical-fault interpretation apply only to the documented 2025 GM system until the exact vehicle circuit is confirmed.

Source: GM monitor, PDF page 190.