The glow plug warning light is a feature of all diesel cars. Glow plugs look very similar to spark plugs, but a glow plug functions by adding additional energy to heat and start a diesel engine.

Why is My Glow Plug Warning Light On?

Unlike some of the other warning lights on your car’s dashboard, the glow plug light is not an indicator of car troubles under normal circumstances. In fact, the glow plug symbol lights up often when we try to start a diesel car in cold weather conditions. The light should turn off in 5 – 10 seconds, or as soon as the car’s engine is hot enough to start. The same glow plug symbol turns into a glow plug warning light if it starts flashing or when the light stays on even after you have managed to start the car.

What is the Glow Plug Warning Light?

Diesel engines require a bit of additional heating in winter before they can be started. As this additional heat is supplied by glow plugs, a glow plug symbol lighting up at this stage only indicates that the plug inside is doing its job. When that same coil light on dash starts to flash or stays on even after the engine starts, that’s when it becomes a glow plug warning light. This coil-shaped warning light will be staying on or flashing as a warning that something is wrong with the glow plug, its timer, or perhaps the diesel engine itself.

What Does it Mean When the Glow Plug Warning Light is Flashing?

It could mean a lot of things, but in most cases, it means that the car won’t be able to start as long as your glow plug warning light is flashing. If the light starts to flash while you are driving, it indicates a sudden loss of power.

This means you will need to call a breakdown repair service or drive on to your nearest service centre or repair garage to have the car properly inspected. In older models, the car may start even when your glow plug symbol is flashing. This is a warning that you should not be driving the car without getting it checked first, even though you may still be able to do so for a while.

How Does the Glow Plug Warning Light Work?

Look for that yellow or orange coil light on dash, which quite literally looks like a double looped coil. That’s the glow plug symbol, which transforms into a glow plug warning light if:

  1. It takes the engine a long time to heat up and the light stays on for longer than 10 – 15 seconds.
  2. The car fails to start at all while the glow plug light stays on indefinitely.
  3. The light stays on even after ignition.
  4. The glow plug warning light starts to flash at any point.

Which are the Common Reasons the Glow Plug Warning Light will Come On?

Cold Weather

If the glow plug coil light on dash comes on when you are trying to start a diesel car in winter, it indicates that the weather is sufficiently cold for your car’s diesel engine to need some extra heating from the glow plug. It is only an indicator at this point and not a cause for concern. If the glow plug symbol refuses to turn off or if it starts blinking, that’s when you know the reason is no longer just the cold.

Failing Glow Plug

If the glow plug light is staying on for longer than 10 – 15 seconds, it indicates a loss of power. The glow plug is losing its power efficiency and it will need to be changed soon. Neglecting to do so can lead to more serious car issues down the line.