Colorado preheating lamp issue

I had almost the exact same symptoms on my Colorado. The preheating lamp staying on, along with the check engine light and smoke, screams preheating control unit issue. Did you check the cable and plug connections to the heating module itself? A defective connection there is a common cause, and often cheaper to fix than replacing the entire unit.

Thanks for the quick reply! When you say check the connections, do you mean visually inspect them, or is there a way to test them? I gave them a once-over, and they looked okay, but maybe I missed something. Is there a specific wire or connector I should focus on? Any tips on how to properly diagnose a faulty connection?

Visually inspecting is a good start, but you need to check for voltage and continuity with a multimeter to properly diagnose a connection issue. Otherwise, you'll be chasing your tail indefinitely. Frankly, unless you're comfortable with automotive electrical diagnostics, I'd strongly suggest taking it to a workshop. Pinpointing the exact wire or connector causing the problem can be tricky without the right tools and diagnostic experience. Save yourself the headache and potential for further damage.

You're right, I think I'm in over my head. I took it to the workshop, and you nailed it - faulty connection to the preheating control unit. They fixed the cable, and the total cost was 95€. Thanks for the advice!