Peugeot 806 Preheating Lamp Issue

The symptoms definitely suggest a preheating control unit issue. The persistent preheating lamp, check engine light, and smoke on acceleration are common signs. A defective cable or plug connection is a likely cause, disrupting the signal to the engine control unit.

How can I diagnose the cable or plug connection? What should I inspect, and are there tests to confirm the fault before replacing the unit?

You'd need a multimeter to check the cable and plug for continuity and voltage. But given the complexity, I'd suggest a workshop visit to confirm the issue.

Took it to a workshop, and it was a corroded connector on the preheating control unit, like we thought. Repair was cleaning and replacing the connector, cost 95€. Thanks for the help.