Diagnostic article Generic OBD-II
P242D: exhaust temperature sensor 3 above its electrical range
P242D identifies an above-range raw input from exhaust gas temperature sensor 3.
Read before applying this article
Documented application
2025 GM 25OBDG04B diagnostic parameter file; the cited monitor is documented, but individual vehicle, engine and calibration applicability has not been established.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P242D checks the upper input range of exhaust gas temperature sensor 3. The GM monitor supports an analog sensor and a digital thermocouple system. The analog criterion is resistance above 100 million ohms; the digital criterion is a raw temperature above 1,289.85°C.
An input fault is not automatically an overheating event
The source frames these limits as electrical-failure detection. For digital hardware it specifically discusses the wiring between the module and probes. A displayed extreme temperature should therefore be assessed for signal validity before being treated as a trustworthy physical exhaust temperature.
The monitor requires valid supply and run/crank, no cranking, no diagnostic reset, no communication loss and completion of sensor initialization. Its counter is 19 failures out of 25 samples at a 100 ms task rate. Reporting is Type A, one trip, unlike the Type B low-range entry.
Confirmation
Establish the installed sensing architecture before comparing any measurement with the relevant limit. A resistance value and a digital temperature are not interchangeable test results. After diagnosis, confirm that the upper-range test completes with valid input and communication. The summary provides no probe pinout or universal replacement conclusion, and it does not justify physically approaching a potentially hot exhaust to investigate the code.
Source and application limits
This explanation covers the cited 2025 GM monitor. Confirm the vehicle and calibration in its service information before applying these limits; inclusion in this file does not establish model compatibility. GM diagnostic parameters, PDF page 1475.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Exhaust Gas Temperature Sensor Circuit High Bank 1 Sensor 3
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT