Seat Toledo diesel engine issue

I had a similar issue with my Opel Astra, also a diesel. The preheating lamp remained illuminated, and the check engine light activated. I recommend you perform a diagnostic test to pinpoint the exact fault. It might be the glow control unit itself, or, as you suggested, a defective cable or plug connection to the component. Does the engine struggle during a cold start, or have you experienced any vehicle stalling?

Thank you for the information. When you experienced the problem with your Opel Astra, did you try anything before taking it to the workshop? I'm interested in what steps you took to troubleshoot the issue.

In answer to your question, I did not perform any troubleshooting beyond visually inspecting the wiring. I lack the necessary diagnostic equipment to properly assess the system. I recommend that you seek professional assistance from a qualified workshop. Continuing to drive the car with a defective heating element could potentially damage the diesel engine. Hopefully, the diagnostic test confirms the cable issue. This would be the best-case scenario.

Acknowledged, I appreciate the insights. I took the Toledo to the workshop, and the diagnostic test showed that the glow control unit was indeed faulty due to a defective cable connection. The repair cost was 95€. The preheating lamp now switches off as expected, and the check engine light is gone. Thank you for your help!