P205B: reductant tank temperature disagrees after a cold soak

P205B is a reductant tank-temperature plausibility code in the reviewed GM controller. At startup, the system compares the tank sensor with a latched average from other valid temperature sensors. The intention is to assess agreement after temperatures have had time to stabilize.

It is not an immediate hot-restart comparison

The startup reference requires an engine-off interval exceeding eight hours and at least four valid temperature inputs. Which sensors contribute is calibrated; the source lists categories such as exhaust, coolant, fuel, ambient and intake temperature. The average must be marked usable and exceed −10°C.

The malfunction criterion is a difference greater than 30°C in either direction. Thus P205B can reflect a tank reading too warm or too cold relative to the reference. It does not directly identify which individual reading caused the disagreement.

Timing and validity

The table lists three failing 0.1-second samples and Type A, one-trip reporting, but also describes a later comparison after reception of the reference mask. Those are separate qualification and scheduling details, not a universal three-tenths-of-a-second startup test. Recovery is listed for the next driving cycle.

Relevant tank-temperature, communication and controller-internal faults must be absent. Verification needs a properly qualified cold-soak reference and usable participating sensors; a warm restart cannot substitute for that condition. The summary does not justify replacing the tank sensor solely from the difference. These criteria are bounded to the documented 2025 GM implementation and require vehicle-specific confirmation before applying its startup procedure.

Source: GM monitor, PDF page 189.