P2031: Ford exhaust-temperature sensor 2 disagrees with its model

P2031 has a broad exhaust-temperature sensor 2 circuit title, but Ford's 2015 diesel summary uses it for sensor-versus-model plausibility. The controller compares the sensor 2 measurement with an expected temperature derived from the preceding sensor's information. This is not the same as the electrical low/high checks.

The monitor needs a defined thermal history

The source requires at least six hours of engine-off time, warm coolant, sufficient engine torque and running time, and a minimum modeled temperature. For sensor 2, the modeled-temperature minimum is 100°C. The comparison runs for 200–400 seconds, with a fault discrepancy required to persist for 20 seconds.

Ford lists a ±80°C model-comparison boundary for sensor 2. Its separate sensor-to-sensor cold-start comparison uses another code and criterion.

Investigate the model chain

Because the expected sensor 2 temperature is based on sensor 1, preserving both readings is more useful than considering sensor 2 alone. An upstream measurement issue can complicate the interpretation; the code does not prove which physical sensor is wrong. Use the exact exhaust configuration and rationality diagnostic procedure rather than replacing sensor 2 solely from the circuit label.

Source and applicability

Ford 2015 model-year diesel OBD system operation summary, revision December 22, 2014; the cited monitor only, without blanket model or engine applicability. Ford source, physical PDF pages 128, 130. The documented monitor explains the fault decision; vehicle-specific service information is still needed for connector identification and a complete repair procedure.