Glow Plug Warning Light: Causes & How to fix

The glow plug warning light on your dashboard indicates issues with the glow plug system, essential for starting your engine in cold weather. A flashing glow plug light signals a malfunction, often pointing to faulty glow plugs or other related components. To fix this issue, you may need to replace worn-out glow plugs, inspect the timer, or perform a diagnostic scan to identify the root cause. 

However, common causes include glow plug control module failure, engine management system issues, wiring or connector problems, faulty glow plugs, and sensor malfunctions. Addressing these causes promptly is essential to prevent further engine problems. 

In cold weather, it’s normal for the glow plug light to stay on longer. Regular maintenance and early repairs can ensure smooth engine performance and prevent long-term damage.

What is a Flashing Glow Plug Light?

A flashing glow plug light on your dashboard is different from a normal glow plug light. The normal glow plug light usually shows as a yellow coil symbol when you start your car, especially in cold weather. However, if the light is blinking, it indicates there is a problem with the glow plug system.

Glow plugs are important for starting your engine in cold temperatures. They help warm the engine, making it easier to start and run smoothly. Once the engine has warmed up enough, the glow plug light disappears automatically. But if the light starts flashing, it means there may be an issue with the glow plug system that needs to be checked.

What is a Glow Plug Warning Light?

A glow plug warning light appears on your dashboard when there’s a problem with the glow plug system. If the symbol keeps flashing and doesn’t go away, it means the glow plug is likely faulty or needs to be replaced soon. The warning light serves to alert Audi owners (or owners of other vehicles with glow plugs) about an issue that requires attention and needs to be fixed.

The purpose of this light is to let you know that something isn’t functioning properly, and it’s important to address it before it affects your engine’s performance.

How to Fix Diesel Glow Plugs Active Warning Light Stays On?

If the diesel glow plug active warning light stays on, it usually means the glow plugs are not functioning correctly. The most common cause for this is the aging of the glow plugs over time. As they go through multiple warm-up cycles, they can wear out and lose their ability to produce heat.

To fix the issue:

1. Replace the Faulty Glow Plugs: If your glow plugs are worn out, replacing them is the first step. Once the faulty glow plugs are replaced, the warning light should turn off, and your engine should function normally.
   
2. Check the Timer: If replacing the glow plugs doesn’t resolve the issue, you may need to inspect the timer in the glow plug system. The timer ensures that the plugs are turned off once the correct temperature is reached. A malfunctioning timer might cause the glow plugs to stay on for too long or not activate at all, contributing to the warning light staying on.
   
3. Get a Diagnostic Scan: If the light persists, a fault code will likely be saved in the vehicle’s computer system. To diagnose the issue, take your vehicle to a certified technician who can use a scan tool to read the code and pinpoint the problem.

How to Fix Glow Plug Warning Light Across Different Car Brands?

The glow plug warning light is an essential indicator in your vehicle’s dashboard that helps you identify issues related to the engine’s pre-heating system, especially in cold conditions. If the warning light appears or flashes, it’s important to address it immediately to prevent further engine trouble. Below are some common causes and solutions for fixing the warning light across different brands.

Nissan

If the glow plug warning light appears on a Nissan vehicle, one possible cause could be a weak or dying battery. A weak battery can trigger the warning light, even if there are no issues with the glow plugs themselves. To fix this:

• Check battery voltage: If the battery is weak, replace it to ensure proper power supply.
• Test glow plugs: If the battery is fine, test the glow plugs to rule out any faults.

Mercedes A-Class

In the case of a Mercedes A-Class, the glow plug warning light typically indicates a fault with one or more glow plugs or the control module responsible for operating them. To resolve this:

• Check individual glow plugs: Test each glow plug to see if any are faulty and replace them if needed.
• Inspect the control module: If the glow plugs are fine, the issue may lie within the control module, which may need to be repaired or replaced.

Peugeot

For a Peugeot vehicle, the glow plug warning light could signify problems related to the engine control unit (ECU) or faulty glow plugs. The most common solutions are:

• Replace faulty glow plugs: If the glow plugs are damaged or worn out, replacing them should solve the problem.
• Diagnose electrical issues: In case the issue is electrical, such as wiring problems or ECU malfunction, diagnostic tools will help pinpoint the exact cause.

Volkswagen (VW)

A flashing glow plug warning light on a Volkswagen vehicle often points to issues with the glow plugs, wiring, or the relay or control module. To resolve this:

• Replace faulty glow plugs: If the glow plugs are worn out, replace them.
• Check wiring: Inspect the wiring for damage or wear and replace any faulty wires.
• Examine the relay or control module: A malfunctioning relay or control module may require replacement.

Audi

A flashing glow plug warning light on an Audi requires immediate attention from a qualified mechanic. Common issues could involve:

• Serious glow plug malfunction: A malfunctioning glow plug may cause the light to flash.
• Engine control problems: The engine control unit might need to be inspected and reset.
• Diagnostic check: Have a mechanic perform a diagnostic check to determine the exact issue.

Amarok 

If the glow plug warning light is flashing on an Amarok, it’s important to get your car diagnosed by a mechanic using a diagnostic scanner. The flashing light could be related to:

• Faulty glow plugs: If the glow plugs are worn out, replacing them should fix the issue.
• Wiring or electrical issues: A diagnostic scan can help identify wiring faults or electrical problems.

By addressing the underlying issue quickly, you can prevent further engine damage and ensure your vehicle runs smoothly.

Causes and Solutions of Flashing Glow Plug Warning Light

The flashing glow plug warning light in your vehicle can indicate a variety of issues, ranging from simple weather-related delays to more serious mechanical problems. It’s important to address the warning promptly, as it may point to faults that could affect engine performance. 

Below are some common causes and their solutions to help you resolve the issue efficiently.

1. Glow Plug Control Module Failure: 

The glow plug control module plays a critical role in managing the functions of glow plugs, such as turning the glow plug light on and off. If the control module malfunctions, it cannot regulate the glow plug’s operations or accurately measure engine heat. This can result in improper engine performance or warning signals.

Solution:

• Diagnose the issue: Use specialized diagnostic tools to confirm whether the control module is faulty. These tools can help detect technical and mechanical issues in your vehicle.
• Replace the control module: If the module is not working properly or failing to control plug functions, replace it with a new one.

2. Engine Management System Issues:

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In some cases, problems with the engine control unit (ECU) or software glitches can trigger the glow plug warning light to blink. These issues can disrupt the normal operation of the engine, leading to improper control of the glow plugs.

Solution:

• Diagnose the ECU: Use diagnostic tools to check for any software issues or errors in the engine control unit (ECU).
• Resolve software issues: If a software problem is identified, reprogram or update the ECU to restore proper functionality and stop the glow plug warning light from blinking.

3. Wiring or Connector Issues:

Damaged wiring or loose connectors can reduce the efficiency of glow plugs. Since the current flows through these wires, even minor damage can disrupt the flow of electricity to other parts of the vehicle. This disruption often triggers the glow plug warning light and affects engine performance.

Solution:

• Inspect the wiring and connectors: Check all wires and connectors connected to the glow plug system for any signs of damage or looseness.
• Repair or replace as needed: If you find a broken wire or faulty connector, repair it or replace it to restore proper electrical flow and ensure the smooth functioning of engine components.

4. Faulty Glow Plugs:

The first step in addressing engine issues is to check the condition of your glow plugs. These components are essential in maintaining engine temperature, particularly in cold weather. Over time, glow plugs can lose their ability to provide the necessary heat to the engine, and signs of wear may start to appear, leading to glow plug warning errors.

Solution:

• Check the condition of the glow plugs: Inspect them to determine if they are faulty or showing signs of wear.
• Replace the glow plugs: If there are signs of damage or wear, replace the faulty glow plugs with new, high-quality ones.
• Test the glow plugs during the warning light issue: If the glow plug warning light flashes for more than 15-20 seconds, this may indicate a power loss, which could lead to further engine faults.

5. Sensor Malfunctions:

Engine-related sensors, such as temperature sensors, are responsible for measuring the engine’s temperature and signaling the glow plug control module to activate or deactivate the glow plug light. When a sensor malfunctions, it sends incorrect signals to the control module. This can result in improper engine heating—either overheating or insufficient heating—and cause the glow plug warning light to blink for an unusual duration.

Solution:

• Use diagnostic tools: Utilize tools like OBD-II to scan for error codes or software glitches to identify the faulty sensor.
• Replace the faulty sensor: Once the problematic sensor is pinpointed, replace it to ensure accurate signals are sent to the control module and to prevent unnecessary glow plug warning lights.

6. Cold Weather: Effects on Glow Plugs

In cold weather, glow plugs need to generate more heat to help the engine start and operate efficiently. The colder temperatures make it take longer for the glow plugs to warm the engine properly, causing the glow plug symbol to remain on the dashboard for an extended period.

Solution:

• Allow more time: During cold weather, be patient as the glow plugs may take longer to heat the engine, and the glow plug symbol may stay on longer than usual. This is a normal response to colder temperatures.

Conclusion

To wrap things up, the glow plug light only poses a risk to your engine if it keeps flashing for an extended period, signaling an issue with the glow plug system. It’s important not to ignore this warning, as it can lead to power loss and a rough driving experience.

If you notice the light, check all related components for any errors. If you’re familiar with the engine system, you can attempt a fix yourself, or else seek help from a professional mechanic. Regular maintenance and prompt repairs are key to keeping your Audi running smoothly and avoiding such problems.

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FAQs:

Q. What does a glow plug warning light on a diesel engine indicate?

A glow plug warning light on a diesel engine indicates a potential problem with the engine’s glow plug system, which is responsible for warming the engine for easier starting, especially in cold weather. If the light flashes, it signals a malfunction that needs to be addressed.

Q. Why is my glow plug light flashing and losing power?

A flashing glow plug light and power loss may be caused by a fault in the EGR valve, wiring system, turbo by-pass system, or sensors. These issues can disrupt the engine’s performance and trigger the warning light.

Q. What should I do if the glow plug warning light is flashing while driving?

If the glow plug warning light is flashing while driving, it suggests a malfunction. It’s recommended to drive cautiously and at reduced speeds until the issue can be diagnosed and resolved.

Q. What does a VW diesel glow plug light flashing and loss of power mean?

A VW diesel glow plug light flashing with loss of power usually indicates a serious engine management system fault that needs immediate attention.

Q. What does the yellow coil warning light mean?

The yellow coil warning light indicates that the engine is taking longer to heat up, and the light stays on for more than 10-15 seconds, which is a normal response in cold weather.

Q. What does it mean if both the glow plug and engine light are on?

If both the glow plug and engine light are on, it usually indicates a problem with the glow plug system in your diesel engine.