Sunny Diesel Glow Plug Problem

That sounds like a glow plug problem. The persistent light and error code point that way. Before replacing the glow plugs, check the glow plug relay and wiring. A bad relay could stop voltage to the plugs, keeping the light on. Damaged wiring can also cause the error. It's easy to check and might save you money. What's the car's fuel efficiency and idle like? Any rough idling or fuel economy drop?

Thanks. I haven't checked the relay or wiring, just the plugs. How do I test the relay and wiring? Also, I've noticed a slight fuel efficiency decrease and occasional mild rough idle, especially when the engine is cold.

The decreased fuel efficiency and rough idle suggest the glow plugs are struggling. If they don't heat right, combustion is less efficient, especially when cold. To test the relay, use a multimeter to check for voltage and continuity. Visually inspect the wiring for damage like frayed wires or corroded connectors. Given the error code and symptoms, it's likely one or more glow plugs are bad. I'd recommend a workshop diagnosis, considering the complexity and tools needed. Replacing the glow plugs and doing a check will probably cost around 440€.

Thanks for the advice. Given your assessment and the worsening symptoms, I'll get it professionally diagnosed and the glow plugs replaced.