P24B7: Particulate-sensor heater resistance changes with temperature

P24B7 identifies particulate-matter sensor heater resistance. Ford’s diesel monitor does not compare resistance with one universal number: its allowed range depends on sensor temperature. That makes the temperature associated with a resistance result essential to its interpretation.

The check is bounded to a key-on opportunity

Ford lists one check per drive at key-on, with a typical duration of ten seconds. Battery voltage must be 11–16 V and particulate-sensor temperature within −30 to 150°C. The entry table also bounds temperature change during monitoring.

At −30°C, the published malfunction limits lie below 1.06 Ω or above 2.93 Ω. At 150°C, they lie below 1.81 Ω or above 4.12 Ω. These endpoint examples illustrate why a cold and a warm heater cannot be judged against the same fixed band. The summary does not publish a complete interpolation or workshop measurement procedure.

Use the monitor context before condemning the heater

A useful verification determines whether the key-on check ran with a valid sensor-temperature input. A resistance value measured after operation, without its corresponding temperature and approved test method, is not automatically comparable with the monitor result.

P24B7 differs from heater-current and off-state-voltage faults in neighboring codes. Preserve those distinctions when reviewing companion faults. The source does not prove that the heater element alone is defective or authorize an external resistance test on an unidentified powered circuit; circuit isolation requires the appropriate service information.

Source and applicability

This explanation follows Ford’s 2023–2024 diesel OBD summary. Match the vehicle’s engine and calibration before applying these monitor values; a generic code alone does not establish fitment. Ford PDF, page 30.