Symptoms
- Cranks but won't catch, especially below freezing
- Glow plug wait light behaves oddly or takes very long
- White smoke on attempted starts
- Starts fine once temperatures rise
Likely causes
- CommonWorn or failing glow plugsGlow plugs preheat the cylinders; if several are weak, cold starts become very difficult.
- CommonWrong fuel blend for the season (summer diesel in winter)Diesel fuel can gel or wax at low temperatures if not winter-blended.
- CommonWeak battery unable to sustain the longer cranking diesels needDiesels typically need more cranking power than gasoline engines.
- PossibleFuel filter clogged with wax/gel in cold weatherWaxed fuel can clog the filter before it even reaches the injectors.
- PossibleFaulty glow plug relay or control moduleEven good glow plugs won't help if the relay controlling them fails.
What to do
- Turn the key to 'on' and wait for the glow plug indicator light to fully go out before attempting to start, even if it takes longer than usual in the cold.
- Check that the fuel used was a winter blend, especially if you filled up in a warmer region before a cold snap.
- Make sure the battery is strong, since diesels demand more cranking power; have it tested if unsure.
- If it doesn't catch after a normal cold-start sequence, avoid excessive cranking, which can drain the battery quickly.
- Check for a fuel filter warning light or symptoms of clogging, such as very hard cranking with no catch at all.
- If parked outside in extreme cold, consider a block heater if your vehicle has one, and plug it in overnight.
- Have the glow plugs and glow plug relay tested if cold starts are consistently difficult.
- For very cold climates, keep the tank topped off and use an anti-gel fuel additive as recommended by the owner's manual.
Tools and parts
- Block heater (if equipped)
- Jumper cables
Glow plugs (set)Search: “diesel glow plugs for [year make model]”
Diesel fuel additive/anti-gelSearch: “diesel fuel anti-gel additive”
When to call a pro
If glow plugs, fuel, and battery all check out and it still won't cold-start, have a diesel specialist check the fuel filter, injectors, and glow plug relay.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.