Are you panicking, seeing the glow plug warning light flashing while driving? Your first question is probably, “Why is my glow plug light flashing?” While our detailed guide on that topic covers all the potential reasons, the good news is that it’s rarely about the glow plugs themselves. This article will focus on the next crucial step: how to quickly identify the problem and fix it with ease using our professional, step-by-step instructions.
A Steady Glow vs. a Frantic Flash: What’s the Difference?
Before you start, it’s important to know what the two glow plug light patterns mean:
- Steady Light – Normal Operation: When you turn the key to the ON position, especially in cold weather, the glow plug light will come on for a few seconds. This is normal—it means the plugs are warming up the engine to help it start. Wait until the light goes off before you start the engine.
- Flashing Light – Warning: If the glow plug light starts flashing while you’re driving or after the engine has started, it’s a warning sign. It tells you the engine’s computer has found a problem. This flashing light works like a “Check Engine” light for diesel vehicles, and your car may go into limp mode, reducing power to prevent damage.
Common Causes of a Flashing Glow Plug Light
The ECU uses this flashing light to report a wide range of issues. Here are the most common culprits discussed by TDI owners, simplified for clarity.
1. The Brake Light System
This is the most frequent and surprising cause. A faulty brake light switch, burnt-out brake light bulbs, or a blown fuse can trigger the light. The ECU relies on the brake signal, and a fault in this circuit, even if the lights seem to work, will cause a warning.
2. Emissions Control System Faults
Modern diesels have complex emissions systems that are common sources of faults. This includes a clogged DPF (Diesel Particulate Filter) needing regeneration, a stuck EGR (Exhaust Gas Recirculation) Valve, or a failed emissions sensor (e.g., DPF pressure or exhaust temperature sensors).
3. Fuel System Issues
The ECU has detected an issue with fuel delivery. This can be due to a clogged fuel filter, incorrect fuel pressure, a faulty fuel injector, or a problem with the fuel metering valve on the injection pump. Symptoms often include poor performance or stalling.
4. Critical Engine Sensor Failure
A sensor providing vital data to the ECU has failed. Common examples include the Camshaft Position Sensor or Engine Speed (Crankshaft) Sensor. A failure here can cause the engine to run poorly, stall, or not start at all.
5. Turbocharger / Boost System Fault
The engine is not producing the correct amount of boost pressure. This is often caused by a faulty boost pressure sensor, a stuck turbo actuator (wastegate), or a boost leak from a cracked hose or loose clamp.
6. Electrical and ECU Issues
A wiring or communication issue can be the cause. This includes frayed wiring on a sensor plug, an immobilizer fault, or a temporary ECU “glitch,” sometimes seen after a battery change.
6 Steps to Tell You How to Fix the Glow Plug Warning Light
Follow this logical workflow, starting with the easiest and cheapest steps first.
1. Don’t Panic. Assess the Situation.
- Is the car still running? A flashing light often comes with a severe loss of power (“limp mode”). Driving is not recommended, as it can be unsafe and may cause further damage. Find a safe place to pull over and diagnose the issue.
- Did the car stall and not restart? This indicates a more serious fault (like a crankshaft sensor or immobilizer issue). You will need to diagnose it where it sits or have it towed.
2. The 5-Minute Roadside Checks
- Restart the Car: Turn the ignition completely off, wait 10 seconds, and restart. Sometimes, a temporary glitch will clear itself.
- Check Your Brake Lights: This is the #1 thing to check. Have someone watch as you press the brake pedal. If they don’t work, you’ve likely found your problem area (bulbs or the fuse).
3. The “ECU Reboot”
As reported by one user, a simple “reboot” fixed their issue after a battery change caused a glitch.
- Disconnect the negative battery cable. (Always disconnect the negative terminal first for safety.)
- Wait for 60 seconds to allow modules to discharge.
- Reconnect the cable securely.
- Try starting the car. If it works and the light is gone, you may have just cleared a temporary glitch. Note: This is not a permanent fix for a real hardware problem.
4. Scan for Codes – The Most Important Step
If the simple checks don’t work, you must read the Diagnostic Trouble Codes (DTCs). The car knows what’s wrong and is trying to tell you.
How to Scan: You can read codes with the ignition key in the “On” position; the engine does not need to be running.
Critical Tool Choice: Generic OBD2 Scanner vs. VCDS
- Generic OBD2 Scanners: These cheap scanners often fail to read VW-specific codes. Many users report that their scanner shows “No Codes Present” even when the glow plug light is flashing.
- VCDS (VAG-COM Diagnostic System) by Ross-Tech: This is the gold standard for VW/Audi owners. It will find the specific, detailed codes that generic scanners miss. If you plan to own a TDI long-term, investing in VCDS is the single best decision you can make.
5. From Code to Solution
Once you have the code from a reliable scanner like VCDS, you have your roadmap.
- If you have a Brake Switch Code (e.g., 16955 / P0571): Replace the brake light switch. It’s an inexpensive part located above the brake pedal.
- If you have an Emissions Code (e.g., DPF, EGR): This may require a “forced regeneration” of the DPF (which can be initiated with VCDS), cleaning the EGR valve, or replacing a faulty sensor.
- If you have a Camshaft/Crankshaft Sensor Code (e.g., 19463 / P0341): This points directly to a failed sensor that needs to be replaced.
- If you have an Immobilizer Code (17978 / P1570): This is often a key-related issue. Try your spare key first.
6. Clear the Codes and Verify the Fix
After replacing the faulty component:
- Use your scanner to clear the fault codes.
- Start the car and take it for a test drive to ensure the light does not return.
Flashing Glow Plug Light: Quick Fix Guide
Use this table to quickly identify the most likely solution based on your car’s symptoms.
| Problem | Quick Solution |
|---|---|
| Light Starts Flashing | Check your brake lights first. It’s the #1 cause. |
| Brake Lights Don’t Work | Check bulbs, the fuse, or the brake switch. |
| Car Stalls After Starting | Likely an immobilizer or sensor (crank/cam) issue. Scan for codes. |
| Car Has No Power (Limp Mode) | Usually an emissions (DPF, EGR) or turbo issue. Scan for codes. |
| Flashes After Battery Change | Try an “ECU Reboot”: disconnect the negative battery cable for 1 minute. |
| Nothing Above Worked | Scan for codes with a VW-specific tool (like VCDS). Generic scanners often fail. |
Conclusion
A flashing glow plug light is a serious warning that should never be ignored. While initially alarming, it’s a problem you can solve with a methodical approach. Follow this guide, identify the problem source, and apply it with the 6-step guide.
During this process, you may need reliable parts to replace the faulty ones. At FridayParts, we understand the urgency. Whether your scan points to a faulty brake light switch, a clogged EGR valve, a tired camshaft sensor, or a DPF pressure sensor, we have the high-quality replacement parts you need to get the job done right. Don’t let a small component keep your TDI on the sidelines.
Visit FridayParts.com to find the exact part for your vehicle and get back on the road fast!
