Electrical
Glow Plug Relay Failure in Diesel Vans — Symptoms and Diagnosis
A failed glow plug relay prevents the pre-heating system from working, causing hard starting in cold weather and increased white smoke.
The glow plug relay supplies power to the glow plugs for a set duration during cold starts. When the relay fails, the glow plugs receive no power and the engine struggles to start, particularly in cold weather. Symptoms include a longer cranking time, white smoke from the exhaust on start-up, and rough idling until the engine warms up. The glow plug warning light on the dashboard may not illuminate at all or may flash. The relay is usually located in the engine bay fuse box and can be tested with a multimeter. Wiring to the relay and plugs should also be inspected for corrosion or damage.
Key takeaways
- A failed glow plug relay causes very hard starting in cold conditions
- The glow plug warning light may not illuminate if the relay is faulty
- Testing the relay with a multimeter confirms whether it is supplying power correctly
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