Symptoms
Ford's own description, and it covers both halves: "an undesirable noise may develop from the cam phasers in the 3.5L GTDI engine. This noise might occur as a rattle when starting the engine after the vehicle was turned off for an extended period of time or as a knocking noise when the engine is idling after it is warmed up." The overnight-start rattle is the one people notice; the warm idle knock is the same problem later on.
Likely cause
The cam phasers are what let the engine shift its valve timing, and they are held in position by oil pressure. Ford's remedy tells you where it looked: the first action was to reprogram the powertrain control module, and only then to replace the hardware. Ford did not publish a root cause in either programme, so this file does not assert one.
How should it be checked?
Ask a Ford dealer to pull the truck's service history and any open field service actions by VIN. **These were customer satisfaction programmes, not safety recalls, so they do not appear on the free nhtsa.gov/recalls VIN check** — a clean result there says nothing about this. Both programmes are closed: 21B10 (the reflash) ran to 31 March 2022, and 21N03 (the phasers) to 1 September 2022 and only for trucks reflashed by 31 August 2021. A truck that got the phasers has had the expensive part of this done at Ford's expense; a truck that got neither is still carrying whatever it started with.
How can you check it yourself?
Arrange to hear it started from properly cold — parked overnight, not warmed up before you arrive. A seller who insists on having the engine running when you get there is worth a second thought on any car, and on this one specifically. Then let it idle until warm and listen again for a deeper knock.
The question to ask the shop
Has a Ford dealer performed 21B10 (the powertrain control module reflash) or 21N03 (cam phaser replacement) on this VIN, and on what date and mileage? What is the build date on the door jamb, and which plant? If the phasers were replaced, were all four done?
