Viano preheating issue diagnosis and resolution

I understand you're experiencing issues with your Viano's preheating system I've seen similar symptoms in Vito models The persistent preheating lamp, check engine light, and smoke do point towards a preheating control unit problem Have you inspected the wiring harness and connector leading to the preheating unit for any signs of corrosion, damage, or loose connections Before replacing the unit, perhaps a thorough electrical continuity test of the wiring would be prudent

Thank you for your response I appreciate the suggestion regarding the wiring harness When you say electrical continuity test, are you referring to checking the resistance between the control unit and the glow plugs themselves Or are there specific pins on the connector that warrant particular attention during this diagnostic procedure

Indeed, checking the resistance between the control unit connector and the glow plugs is a good starting point However, I would also suggest checking the voltage supply to the preheating unit itself Is the unit receiving the correct voltage when the preheating cycle is initiated It is possible the unit itself is not getting sufficient power Given the symptoms, and the potential complexity of car electronics, consulting a qualified workshop may be a worthwhile investment to avoid further complications They can perform a more in-depth diagnosis using specialized equipment

Your advice was invaluable Following your suggestion to meticulously examine the wiring and voltage, I located a partially corroded connector pin After cleaning and applying dielectric grease, the preheating lamp now operates correctly, and the check engine light has extinguished itself The smoke during acceleration has also disappeared It appears the cable was indeed the defective part I appreciate your time and expertise This resolves the issue