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VW Golf Mk4 1999

JohnKasino

Registered
Can someone advise me on how to test the glow plug relay circuit. I've tested the plugs and the relay but still got a cold start problem and think the plugs aren't warming up.
 

cactikid

VIP Member
If you have a circuit tester 12v what we do is remove the rail feed from glow plugs and connect earth connection to + terminal and tip circuit tester onto each plug to see if it lights,any that dont light up is a dead glow plug so would replace all 4.

Do you have a glow plug light which illuminates when you switch the ignition on? Is this light behaving normally, ie on for a few seconds, then off? If it is, then it is possible that the glow plug control unit/relay/timer has gone faulty. There should be 12 volts across the glow plugs when the light is on. I would start by checking this, first. No volts would indicate a faulty relay/fuse. Volts for too short a time would indicate timer/control unit.

If you have changed the glowplugs and it improved for a while, then it may be the timer unit. (new plugs, better glow for a short time, enough for an easier start.)

Have a look at the glow plug relay, relay 4a. You can measure the volt drop across the contacts with the engine running to give an idea of its condition, you could also clean the relay contacts (inside the can) with electrical contact cleaner, etc, or just replace the relay.
 

JohnKasino

Registered
I have had all plugs out and they are all under 1 ohm. I tested the glow plug relay (103) out of the car and it has continuity. The glow plug light only stays on for 2 seconds then goes off. I don't know if the relay is receiving power?
 

cactikid

VIP Member
Possibly wondering if its in the plastic cooling pipes over gearbox might be switches in there with a hairpin.
Petrol engines were always getting replaced lol

Code reader should log a fault if faulty.
 

JohnKasino

Registered
The sensor was under the airflow pipe. Going to fit tomorrow and try. Forgot to say when I took the plugs out I warmed them up and they were all good.
 
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