Citan preheating lamp and check engine light problems

Sounds familiar. I had a similar issue with my Citan, though I didn't see smoke. Preheating lamp wouldn't go off, engine light popped on. Did you check the connections to the heating module itself? Is there any visible corrosion or damage to the wiring harness? Could be a simple electrical fault.

I visually inspected the connections, but I did not see anything obvious. Where is the heating module located? Is it possible to test the connections with a multimeter, or is that too risky without proper diagnostic equipment?

Tracing car electronics issues can be a pain without the right tools. The heating module is usually near the engine block. You could try a multimeter, but you might end up doing more harm than good. My advice? Take it to a workshop. They'll diagnose it properly and save you the headache. Could be a defective part, like the car preheater itself.

I took the vehicle to a workshop. The diagnosis confirmed a defective preheating control unit, specifically an issue with the electrical connector. The repair cost 95€. This resolved the preheating lamp and check engine light issues.