P2D45: reductant heating response compared with a temperature model

The generic P2D45 description is reductant temperature too low, but the cited row is labeled “Reductant Heater 1 Temperature Response Matured Diagnostic.” It compares measured average reductant temperature with a controller estimate for a limit-acceptable heater response, called WPA. A second model represents a nonfunctional heater, called BPU.

This is not just a cold-weather threshold

The diagnostic requires an engine-off period above 28,800 seconds, valid primary and secondary temperatures, valid ambient temperature and more than 150 seconds for temperature initialization. Average reductant temperature must be between −40°C and −14°C, estimated fluid quantity above 5 liters and a heater power command above its listed threshold.

The WPA and BPU predictions must differ by more than 2°C. That separation gives the model an opportunity to distinguish heating behavior. A refill/drain indication or excessive ambient variation can invalidate the comparison. The table uses a 600-second time basis and one decision per driving cycle.

What remains uncertain

The printed malfunction expression and threshold are not sufficiently clear to turn into a universal pass/fail temperature instruction. This article therefore explains the supported modeled-response mechanism while retaining that source issue for review.

For diagnosis, preserve heater command, both measured temperatures and the model states. A cold tank alone does not reproduce the monitor. Verification requires the exact controller procedure and a qualified cold-soak heating event; a warm restart cannot substitute for the required initial conditions.

Source and applicability

Documented 2025 GM gm-2025-04b monitor only; vehicle, engine and controller applicability must be established separately. GM monitor table, PDF page 211.