P220F: Tailpipe NOx heater sensing can fail even when some heating occurs

P220F concerns heater sense range/performance for bank-one sensor two in Ford’s tailpipe NOx section. The documented checks include an open-heater current threshold and a heater-control rationality comparison. A sensor that becomes warm is therefore not automatically evidence that every P220F check passes.

Current and control effort answer different questions

Ford gives heater current below 0.4 A for the open-circuit branch. Its rationality branch uses heater duty cycle differing from expectation by more than 20%. These are distinct observations: low current concerns the electrical response, while the duty comparison needs a valid expected control value.

The page also lists short-to-battery and short-to-ground detection using differential heater-voltage information. Those internal diagnostic quantities should not be converted into arbitrary connector measurements without the correct service procedure.

Keep the downstream sensor identity intact

P220E belongs to the upstream heater family elsewhere in the same document. P220F’s tailpipe location and monitor details should be retained, rather than assuming the two sensor assemblies have interchangeable electrical tests.

Useful verification identifies the precise heater failure detail and the applicable sensor’s operating status. The sensor section lists dewpoint as an entry condition but does not provide a complete warm-up or replacement procedure. It also leaves the general events-per-trip field unspecified. Consequently, a definitive event count or a universal part-replacement rule cannot be taken from this summary; those details must come from the vehicle’s 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 26 · Ford PDF, page 27.