Car preheating warning light: what you need to know

Due to their design, some diesel engines sometimes require starting assistance, especially in cold weather. They are equipped with glow plugs that help heat the air / fuel mixture in the combustion chamber to ensure your vehicle's engine starts efficiently.

The temperature inside the cylinders is increased by the glow plugs during the process. This helps to build up pressure and convert diesel fuel into energy. It will take some time before the engine is fully warmed up and ready to start.

The dashboard of the vehicle is equipped with a variety of symbols that allow the driver to know the status of various parts and various systems. This includes a preheat indicator represented by a coil symbol.

The glow plug indicator can come on for several reasons. This guide will help you learn a little more about this dashboard component of your diesel vehicle.

🚗 What is the role of the preheat indicator light?

Spark plugs are not used in diesel engines. It is the heat generated during very strong compression to ignite the air / fuel mixture in the cylinders that allows this type of engine to operate. When your car is stationary, especially in winter, you may have difficulty starting it.

Glow plugs are designed to solve this problem. They heat the air in the cylinder, causing the coil symbol to light up on the dashboard. After starting the engine, the glow plug no longer plays any role in the combustion process. The time it takes for a glow plug to warm up depends on the vehicle and the ambient temperature.

Typically, glow plugs heat up the engine for five seconds to one minute. At this point, the orange coil indicator on the dashboard should turn off, allowing the driver to start the vehicle.

Indirect transmission vehicle case

The glow plug is more suitable for the indirect injection diesel engine. If, for a direct injection vehicle, the glow plug function is terminated when the engine is air-conditioned, there are additional functions in the case of indirect injection. In this case, the orange coil indicator serves as an additional post-heating function.

To avoid overly toxic fumes, the indirect injection diesel engine is equipped with spark plugs that will continue to heat up even after starting the vehicle until the required temperature is reached. This function is also useful for reducing noise associated with various reactions in the engine. After the start of the post-heating process, the indicator lamp goes out.

The Specific Case of the HDI Diesel Option

If you own a vehicle in this class, it can be difficult to understand all the functions of an incandescent bulb. The coil symbol is present on the dashboard of an HDI diesel vehicle, although the engine does not need to heat up to start properly.

The indicator light's role here will be to alert you to emissions and noise while the spark plugs provide additional heat. For this type of vehicle, a flashing or steady light does not necessarily indicate a malfunction. You will need to check the condition of the spark plugs with an ammeter. If they are in good condition, you will need to think about a more serious problem requiring diagnosis in your garage.

🔎 Why should the lights go out before starting?

Since the timing for activating the coil symbol after inserting the ignition key corresponds to the preheating of the direct injection engine, it is important that this period be observed for the proper functioning of your vehicle. If you get into the habit of shortening this adjustment period, the motor heating elements may be damaged.

You have to wait for the preheat light to go out, for the sake of respect for the planet. Compliance with the operating time of this indicator light helps to reduce greenhouse gas emissions as well as reduce noise. In addition to glow plugs, diesel engines can also use other starting aids, including:

● Coolant heater;

● Kit for the introduction of ether;

● Oil pan heater;

● Heater block;

● Air intake heater.

💡Why is the preheat indicator flashing?

If the coil symbol flashes, this indicates a possible malfunction. In this case, the indicator light may turn red or yellow, depending on the model. Most often, this is a benign electrical circuit malfunction associated with a false contact. In the most serious cases, these can be:

● Problems with the exhaust gas recirculation valve;

● loose or damaged glow plugs;

● power loss;

● Malfunction of the preheating timer;

● Fuel filter clogged;

● Lack of engine maintenance;

● Short circuit of the preheating relay or injection pump.

A direct or indirect problem with the glow plugs can result in a loss of acceleration or an overall loss of engine power. You may also notice a drop in fuel consumption or even a misfire in the chamber.

While there is no quick fix for a specific problem, a qualified technician should be able to identify and fix the problem.

🔧 What if the light is off?

When you insert the key into the ignition switch, you notice that the coil symbol does not light up. Think of the dashboard light first. Replace this. If the incandescent lamp still does not light up, the problem is more serious.

In other cases, your engine may overheat, but the light will still remain on after the engine acclimatization time has passed. These are signs of a problem with the organ responsible for preheating the air in the combustion chambers. Your engine can overheat or even drown if you don't do something very quickly.

If you are not familiar with mechanics, it is best to consult a professional to fix the error.

⚡ Can I drive with the warning light on?

A flashing glow plug warning light alerts the driver of a potential problem. Therefore, it is important to take warnings seriously and check them whenever possible. Driving your diesel vehicle with a glow plug on will depend on whether it blinks or not.

If the coil symbol is solid, most vehicles cannot start until it shuts down and the engine is fully warmed up. This is especially important if your vehicle is over 20 years old. On newer models of vehicles with direct injection diesel engines, the coil symbol may flash or remain on.

If the warning light is flashing, you can continue driving, but not recommended. For example, you can drive a car if you want to deliver the car for a major overhaul, and the breakdown site is not far away. Drive without speeding to avoid damaging other parts.

If you ignore your vehicle's call, it can go into a “safe” or “degraded” mode and thus limit your engine's performance to avoid propagation of failures.