Volkswagen Glow Plug Warning Light — What It Means & How to Fix It

What Does This Error Mean?

The VW glow plug warning light (a coiled wire symbol) on a diesel engine means the glow plug preheating system has a fault. Glow plugs heat the combustion chamber to help a diesel start in cold weather. A faulty glow plug causes hard cold starts and rough running until the engine warms up. Read the fault codes to identify which plug has failed — they are numbered by cylinder.

Affected Models

VW Golf TDI
VW Passat TDI
VW Tiguan TDI
VW Polo TDI
VW Caddy TDI
VW Touareg TDI
VW T-Roc TDI
VW Transporter TDI

Common Causes

Failed glow plug in one or more cylinders — glow plugs typically last 60,000-100,000 miles
Faulty glow plug relay or control module
Open circuit in the glow plug wiring harness
Corroded or loose glow plug connector
Glow plug seized in the cylinder head — common on high-mileage engines

How to Fix It

Read the fault codes with a VW-compatible scanner.

The glow plug fault codes are numbered by cylinder — P0670 through P0679 indicate individual glow plug circuit faults for cylinders 1-8. A standard OBD-II reader reads these codes. The code tells you exactly which cylinder has the faulty plug.
Test the glow plug resistance with a multimeter.

Disconnect the glow plug connector and measure resistance between the plug terminal and engine ground. A healthy glow plug reads 0.5-2 ohms. An open circuit (infinite resistance) means the plug has failed internally. This test confirms the plug is faulty before you commit to replacement.
Replace the faulty glow plug — but proceed with care on high-mileage engines.

Glow plugs on high-mileage VW diesels are notorious for seizing in the cylinder head. Always heat the area around the plug with a heat gun before attempting removal. Forcing a seized plug without heat causes it to snap off in the head — an expensive repair.
Check the glow plug relay and wiring if the plug tests fine.

If the plug resistance is correct but the fault code persists, test the glow plug relay — it sends power to the plugs on a signal from the ECM. A failed relay prevents all glow plugs from operating even when the plugs themselves are healthy.
Replace all glow plugs as a set if multiple cylinders are affected.

Glow plugs wear at similar rates. If two or more have failed, all four are likely near end of life. Replacing all four at once avoids a return visit shortly after for the remaining plugs.

The Volkswagen glow plug warning light — a symbol that looks like a coiled wire or spring — is exclusive to diesel models. Petrol engines do not have glow plugs, so if you see this light you are definitely driving a TDI diesel. The glow plug system pre-heats the combustion chambers before a cold start, allowing the diesel fuel to ignite reliably in cold temperatures. When this system has a fault, cold starting becomes more difficult and the check engine light often accompanies the glow plug warning.

Why Glow Plugs Matter in a Diesel

Petrol engines use a spark plug to ignite a fuel-air mixture. Diesel engines use compression heat — the air in the cylinder is compressed so intensely that it heats up to over 700 degrees Celsius, which is hot enough to ignite injected diesel fuel spontaneously. This works well when the engine is warm. In cold weather, the cylinder walls and piston are cold, absorbing heat from the compressed air before it can reach ignition temperature. Glow plugs solve this by pre-heating the combustion chamber for a few seconds before the engine cranks, ensuring there is enough heat for reliable ignition even on a very cold morning.

The Seized Glow Plug Problem

The most important thing to know about VW glow plug replacement is the risk of seized plugs on high-mileage TDI engines. The glow plugs are threaded into the aluminium cylinder head, and over years of heat cycling, the steel plug body bonds to the aluminium via a corrosion process. Attempting to remove a seized plug with normal torque causes it to snap off, leaving the ceramic and steel body stuck in the head — requiring specialised extraction tools and significantly increasing repair cost. Any mechanic replacing glow plugs on a high-mileage VW TDI should heat the area thoroughly and use penetrating oil before attempting removal.

One Plug or All Four?

When a single glow plug fault code is stored, it is tempting to replace only that one plug. However, glow plugs on the same engine degrade at similar rates. If one has failed, the others are likely within a few thousand miles of failure. Replacing all four at the same time is more cost-effective in the long run, and avoids the risk of each successive plug replacement on a high-mileage engine where seizure risk increases with age.

Frequently Asked Questions

Can I drive a VW diesel with the glow plug warning on?

Yes, once the engine is fully warm. Glow plugs are only needed for cold starts — once the diesel is running and at operating temperature, the combustion process is self-sustaining. You may experience rough running and difficulty starting from cold until the faulty plug is replaced.

Why do VW glow plugs seize in the head?

VW TDI engines run at very high temperatures and glow plugs are exposed to extreme heat cycling. Over many years, the corrosion between the steel plug body and the aluminium cylinder head creates a chemical bond that makes removal very difficult. Heating the area and using penetrating oil before removal significantly reduces the risk of snapping the plug.

How often should VW glow plugs be replaced?

VW glow plugs typically last 60,000-100,000 miles under normal use. They do not have a fixed service interval — replacement is triggered when one fails. Some VW specialists recommend proactive replacement at 100,000 miles to avoid the risk of seized plugs, which become increasingly likely on older, higher-mileage engines.