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:
- It takes the engine a long time to heat up and the light stays on for longer than 10 – 15 seconds.
- The car fails to start at all while the glow plug light stays on indefinitely.
- The light stays on even after ignition.
- 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.
Worn-Out Glow Plug
In case the glow plug light stays on for a long time without facilitating ignition, a completely worn-out glow plug is likely to be the cause. In most instances, the coil warning light will start flashing after a few seconds, indicating a glow plug’s complete loss of power.
Malfunctioning Sensor-Timer
A timer fitted with temperature sensors is responsible for turning a glow plug on and off as needed. If the attached sensors malfunction, the timer will be unable to turn the glow plug on or off at the right time. This can result in both underheating and overheating of the engine. You will be warned about such malfunctions by your glow plug warning light in advance, as it will either start flashing or stay on for longer than usual. Ignoring these warnings will eventually lead to engine damage down the line.
Is It Dangerous to Drive When My Glow Plug Warning Light is on?
If the glow plug warning light is not flashing but it remains on after ignition, you should wait until it turns off before driving. The 15-second rule is valid but wait for a few minutes if you must. While slower heating is a warning sign and you should get your car checked professionally as soon as possible, it’s still a lot less dangerous than starting to drive the car with its glow plug light still on.
In case you see the engine warning light flash simultaneously with the glow plug warning light, that indicates an overheating engine. Rare as the combination is, it’s a potentially dangerous situation and you will need to slow down first, before pulling over cautiously on the side of the road. Do not pull over right away or stop suddenly because doing so can and often will lead to a car accident.
What Colour is the Light? The shade depends on your car’s make and model, but glow plug warning light indicators are yellow or orange double looped coil lights on the dashboard.
Will My Car Fail Its MOT if the Glow Plug Warning Light is On?
If the weather is cold and your glow plug light turns off after a reasonable amount of time, it will not fail its MOT. At the same time, a flashing coil warning light will not let the car pass its MOT. The same applies if the glow plug symbol stays on for longer than expected during the test.
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