P242A: Ford exhaust-temperature sensor 3 model-plausibility fault

Ford's 2015 diesel summary maps P242A to exhaust-temperature sensor 3 versus model plausibility. The model for sensor 3 is based on sensor 2. A discrepancy therefore needs to be interpreted within the sequence of exhaust measurements, rather than as an isolated continuity failure.

Conditions and persistence

The monitor follows a qualifying cold start after at least six hours off. Ford lists warm coolant, minimum running time, sufficient engine torque and a modeled sensor 3 temperature of at least 95°C among the entry conditions. The comparison window is 200–400 seconds, and the discrepancy must persist for 20 seconds.

Sensor 3's listed model boundary is ±60°C. The separate sensor-to-sensor comparison has its own code, so a generic range/performance description should not erase which comparison failed.

Preserve upstream evidence

Record sensor 2, sensor 3 and the applicable modeled value if available. A model driven by another measurement can be affected by the quality of that upstream information. P242A alone cannot identify whether the sensor, its circuit or the thermal assumptions are responsible. Use the correct exhaust layout and rationality diagnostic procedure before deciding on a component replacement.

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.