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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22242
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a Golf Mk5 170hp GT TDI Diesel (2006) with 80,000

Resolved Question:

I have a Golf Mk5 170hp GT TDI Diesel (2006) with 80,000 miles which has just started having trouble starting in the cold weather. It's just quite suddenly started with no previous issues. There is no black smoke or anything when starting, but it turns over slowly and won't start first time, then starts after a few turns the second time. It has always started (in the end) but I wonder if I should do something about it now before it gets worse and before winter really starts. As a non-technical person, my first instinct is that it would be the glow plugs? But I don't really know if maybe it's just getting a bit old?? I would rather not spend too much money on it, since it is quite an old car anyway.
Submitted: 22 days ago.
Category: Car
Expert:  Matt replied 22 days ago.


I'd agree that it sounds like glow plugs so check that you're getting full power to the glow-plugs, they pull a lot of current so take care when checking but see if the relay is clicking when the ignition is turned on first and also check the fuse if this is OK check to see if the engine earth strap is also OK.

If the plugs haven't been changed in the last 20K then they may have to be replaced.
You can test the glow-plugs with a multimeter by measuring the resistance across the plug ( between the power connection and the body) it should be around 4-8ohms if its tending to infinity / open circuit the plug is faulty or by using a clip on current clamp, either on the supply wire to glow plugs or onto engine earth, with glow plug light on you should see 15-20amps for each glow plug fitted, 4 cylinders would be approximately 60-80amps.

Also if its not injecting at all then check the connections to the crankshaft sensor, unplug it and check for corroded contacts and broken wiring, and consider fitting a new sensor - do the same for the cam position sensor
If the EGR valve is stuck open then this too can effect starting so try disconnecting it to see if this helps or changes anything

Could also be an injector leaking fuel back through the overspill pipe, so not getting enough fuel pressure to tell ECU to fire the injectors, this is trickier to find and you’ll need the garage to do a ‘run back’ test to identify which one is the issue
Lastly it’s also worth considering fitting a new fuel filter as if only slightly blocked this can lower fuel supply pressure and choke the main pump, the pump will be more sensitive to this when its cold as diesel thickens considerably with low temperatures.

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