Skip the auto shop - Our mechanics make house calls

Symptoms of a Bad or Failing Glow Plugs & Timer

glow plugs and timer

Bad or Failing Glow Plugs & Timer Inspection

by a top-rated mechanic at your home or office

Glow plugs and glow plug timers are engine management components that are found on vehicles equipped with diesel engines. Instead of using spark plugs to incite combustion, diesel engines rely on cylinder pressure and temperature to ignite the fuel mixture. Since temperature can be considerably lower during cold starts and in cold weather conditions, glow plugs are used to help warm up the engine cylinders to an adequate temperature that will allow for proper combustion. They are so called because they will glow a bright orange color when current is applied to them.

The glow plug timer is the component that controls the glow plugs, setting the time that they stay powered on for, making sure that they stay on long enough to adequately warm the cylinders properly, but not so long that the glow plugs sustain damage or accelerated wear.

As the glow plugs and their timer play a major role in starting the vehicle, when any of those components have a problem, it can cause driveability issues with the vehicle. Usually a bad or failing glow plug will produce a few symptoms that can alert the driver of a potential issue.

HAVE SYMPTOMS OF CAR TROUBLE?
Get an $80 diagnostic
by a top-rated mechanic at your home or office.

Get a quote · Book an Appointment · Our expert mechanics come to you.

1. Hard starting

One of the first symptoms that is commonly associated with problematic timer or glow plugs is hard starting. Faulty glow plugs will be unable to provide the additional heat required to help the engine start normally, while a bad timer may cause them to operate at incorrect intervals. Both issues may cause starting problem with the engine, which may be especially pronounced during cold starts and in cold weather. The engine may require more cranks than normal before it starts, may require several tries before it starts, or may fail to start at all.

2. Glow Plug Light comes on

Another symptom potential issue with diesel glow plugs or their timer is an illuminated Glow Plug Light. Some diesel engine equipped vehicles will come with an indicator on the instrument cluster that will illuminate or flash if the computer detects that there is an issue with the glow plug system. The indicator is usually a line in the shape of a spiral or coil, reminiscent of a wire filament, and amber in color.

HAVE SYMPTOMS OF CAR TROUBLE?
Get your car fixed at your home or office.

Get a quote · Book an Appointment · Our expert mechanics come to you.

3. Check Engine Light comes on

An illuminated Check Engine Light is another symptom of possible issue with the glow plugs or timer. If the computer detects an issue with the circuit or signal of any of the glow plugs, or the timer, it will set off the Check Engine Light in order to notify the driver of the issue. The light will usually come on after the vehicle has already begun to experience starting issues. A Check Engine Light can also be activated by a wide variety of other issues, so having the computer scanned for trouble codes is highly recommended.

While replacing the glow plug timer is not generally considered routine maintenance, glow plugs usually have a recommended interval that they should be serviced at in order to avoid potential issues. If your vehicle is displaying any of the symptoms above, or you suspect that your glow plugs or the timer may be having an issue, have the vehicle inspected by a professional technician, such as one from YourMechanic, to determine if any of the components need to be replaced.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Still not sure about your car's issue?
Diagnose your car
What kind of issue are you experiencing?
Brakes are squeaking
Car is not starting
Car is overheating
Car is shaking (vibrating)
Fluids are leaking
Heating and A/C
Smoke or steam is coming out of the car
Warning light is on
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

How to Buy Fuel Treatments
Adding a fuel additive to your gas tank when you fill up is one way to clean vital engine parts of deposits, improve the performance of your engine,...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
P0291OBD-II Trouble Code: Cylinder 11 Injector Circuit Low
P0291 code definition When your vehicle’s PCM registers the P0291 code, it means that a voltage reading came from the fuel injector circuit – for cylinder number 11’s fuel injector –...


Related questions

Q: Glow Plug System light comes on sometimes and engine has a lack of power when the light is on.

Hi there. Check the glow plug relay and see if its plugged in. Check the circuits to the glow plugs and see if there is power to them when the key is turned on. The circuit to the glow plugs...

Q: Car will not start, no spark - 1994 Ford E-350 Econoline Club Wagon

Besides checking the engine and fuel injection fuses and relays, it is possible the oil pressure cutoff switch may be malfunctioning since the vehicle sat up so long without oil pressure. If the engine oil pump isn't priming, there might...

Q: Stalling at cold start, replaced idle air control valve 1990 Chevy P30 6.2 l diesel

Hi - there are a few other component problems that could be causing your poor cold starting. One or more failed glow plugs and air leaks in the air intake will cause poor cold-start and cold-running behavior. I would recommend...