Mondeo preheating fault

The symptoms you describe are indeed indicative of a potential malfunction within the preheating control system. Could you please provide additional information regarding the diagnostic trouble codes (DTCs) retrieved by your scanner? Furthermore, have you conducted a thorough inspection of the wiring harness and associated connectors for signs of corrosion, damage, or loose connections?

The code I pulled was P0670 - Preheating control circuit malfunction. I've given the plugs a wiggle and a prod, but nothing obvious jumps out. By any chance are there any usual culprits I should be checking more carefully on this heap?

Based on the diagnostic trouble code P0670 and your description of the troubleshooting steps undertaken, it is probable that the root cause of the issue resides within the preheating control unit itself or the associated wiring. While further diagnostics may be performed, it is recommended to seek the counsel of a qualified automotive technician for comprehensive evaluation and repair.

Took it to a garage and as suspected it was a faulty connection to the heater control unit. Sorted for 95€. Thanks for confirming my suspicions!