P0546: EGT sensor 1 above its raw electrical range

P0546 is a high-range exhaust-gas temperature sensor 1 check in this GM implementation. The strategy accommodates either analog resistance data or a digital thermocouple temperature report.

The threshold depends on architecture

The analog boundary is resistance above 100,000,000 ohms. For the digital path, the boundary is reported temperature above 1,289.85°C. These are alternative representations of electrical validity, not values to demand simultaneously from every vehicle.

A high digital report by itself does not prove actual exhaust overtemperature; the monitor can identify integrity problems between a thermocouple module and its probes. Correctly identifying the raw channel changes the next diagnostic check.

Wait for valid sensor operation

The table requires the initialization delay to have elapsed, no lost-communication error, valid supply, active run/crank ignition, no diagnostic reset and an engine outside cranking. It filters 19 failures among 25 samples on a 100 ms task and lists Type A, one-trip reporting.

For verification, establish a valid initialized signal under those conditions and use the applicable architecture's service limits. A normal value before initialization or an absent test while communication is lost cannot establish recovery. The page provides no universal probe location, connector test or replacement conclusion. Diagnosis should separate the sensor, its reporting module and their connections through vehicle-specific service information.

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 1216.