P0545: EGT sensor 1 low-range feedback and a source limitation

P0545 checks exhaust-gas temperature sensor 1 for a low raw signal in the cited GM strategy. It supports analog resistance-based and digital thermocouple implementations, so the correct signal type must be established first.

A usable digital criterion, an unresolved analog value

For the digital path, the source gives a reported temperature below −72.80°C. This is an electrical-validity boundary, not a claim that the exhaust actually reached that temperature.

The analog column prints a resistance below zero ohms. That is not a credible physical resistance test to apply as written, and this article does not silently replace it with a guessed value. The analog criterion remains subject to source or calibration review.

Monitor eligibility matters

The check requires no cranking, valid supply, active run/crank ignition, no diagnostic reset and no lost-communication error. A calibration-dependent initialization delay must have elapsed. The table specifies 19 failures among 25 samples on a 100 ms task, with Type B reporting.

Identify the installed sensor architecture and confirm initialization and communication status before evaluating a low value. Absence of the code during initialization is not a passing test. Verification should use the exact vehicle's approved signal limits and circuit procedure. The summary does not establish a failed probe independently of its module or wiring.

Source and applicability

2025 GM 25OBDG04B diagnostic parameter tables; the cited monitor only. Vehicle, engine and calibration applicability must be confirmed separately. These tables describe detection logic, not a complete repair procedure or a component replacement verdict. gm-2025-04b, PDF page 1215.