Glow Plug Light (Diesel)
What it means
Found on diesel cars and shown in amber as a coil spiral, this light at key-on means the glow plugs are preheating the combustion chambers, which is normal; wait for it to go out, then start the engine. If it flashes or stays on while driving, there is a fault in the glow system, and on some makes an engine management fault.
Codes that may appear with it
The most common stored codes that may turn this light on; scan the car with an OBD reader to find the actual code.
Symptoms4
- The light flashes or stays on after the engine starts.
- Hard starting, especially on cold mornings.
- White smoke and a rough engine right after starting.
- Loss of power if the light is signaling an engine management fault.
Possible causes6
- One or more failed glow plugs.
- Faulty glow plug control unit or relay.
- Damaged wiring or connections to the plugs.
- Weak battery that cannot supply enough current to the plugs.
- Faulty coolant temperature sensor causing incorrect preheating.
- On some makes, an engine fault such as fuel pressure or a sensor shown by this light flashing.
How to diagnose5
- Check whether it glows for a few seconds at key-on and then goes out; that is normal.
- If it flashes while driving, slow down and read the codes at the first chance.
- Read the engine codes with a scan tool that supports diesel engines.
- Check the battery voltage and condition.
- The workshop measures each plug's resistance and current and checks the control unit and wiring against the manufacturer specification.
How to fix6
- Charge or replace a weak battery.
- Repair damaged wiring or connections.
- Replace the failed glow plug; on older engines replacing the full set is often better.
- Replace the glow plug control unit or relay if confirmed faulty.
- Repair the engine fault the codes point to if that is why it flashes.
- Clear the codes and confirm the light goes out a few seconds after key-on.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
In the Saudi market: SAR 200–2,500 (≈ USD 53–667)
Our prices come from the Saudi market, converted at a fixed rate (SAR 3.75 per USD). Prices in your country may differ a lot, so we show the cost level.
The cost starts with a wire repair or a single plug, and rises for a full set, a new control unit, or plugs seized in the cylinder head that need careful removal.
Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026
Frequently asked questions
Should I wait for it to go out before starting?
Yes, especially in cold weather. Waiting means the chambers are warm enough, so the engine starts more easily with less smoke.
Why does the light flash while driving?
Flashing means a glow system fault, and some makes also use it for an engine management fault, so read the codes soon and drive gently.
Why does my car start fine in summer despite bad glow plugs?
High air temperatures help diesel ignite with little preheating, but the fault shows on cold mornings and can increase smoke and emissions.
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