Audi A4 2.0 tdi 170 2007 - How do I test glow plugs

Honest John Back Room » Technical matters
View Threaded
Fri 4 Nov 2011 10:32
Audi A4 2.0 tdi 170 2007 - How do I test glow plugs - mm707

Hi,

Can anyone give me an idiots guide of how to test the glow plugs ?

The car is taking quite a few turns to get started in the morning but is fine after that - suspect glow plugs but would like to test myself if possible

Many thanks

Reply | Report as offensive | Link
Fri 4 Nov 2011 12:17
Audi A4 2.0 tdi 170 2007 - How do I test glow plugs - Peter.N.

Disconnect the leads so all the plugs are isolated from each other then check the resistance between each plug terminal and earth, if the plugs are good they should read one ohm or less, any completely dud ones will not read at all. Alternatively you can take each plug out and connect across the battery, they should glow red after a few seconds. Yet a third way is to isolate them and touch a wire connected to the battery + onto each one in turn, you should get a small spark.

Reply | Report as offensive | Link
Fri 4 Nov 2011 12:19
Audi A4 2.0 tdi 170 2007 - How do I test glow plugs - daveyjp

Have you tried cycling the glow plugs to get more heat into the cylinders?

Turn the key until all lights on dash are on, turn off, do this two or three times then see how it starts.

if there is still a problem it could be more than a single glow plug failure.

Edited by daveyjp on 04/11/2011 at 12:22

Reply | Report as offensive | Link
Sun 6 Nov 2011 16:55
Audi A4 2.0 tdi 170 2007 - How do I test glow plugs - paulc924

Be careful. Your battery will give 12 volts when some of these work at lower voltages. Don't blow them when testing them.

Reply | Report as offensive | Link
Mon 7 Nov 2011 12:29
Audi A4 2.0 tdi 170 2007 - How do I test glow plugs - mm707

Many thanks for the advice

Reply | Report as offensive | Link
Mon 7 Nov 2011 18:53
Audi A4 2.0 tdi 170 2007 - How do I test glow plugs - Peter.N.

Another way to check is to connect a voltmeter across the battery, when the plugs are operating you should see about half a volt or so drop.

Reply | Report as offensive | Link
Mon 7 Nov 2011 23:38
Audi A4 2.0 tdi 170 2007 - How do I test glow plugs - 659FBE

Be very careful - this is a late VAG diesel and it will have low voltage (ie less than 12V) plugs. Typically, they will be rated at 5V or 7V.

The system is designed such that they initially receive 12V to heat them up quickly but the voltage is then reduced by mark/space ratio control to give a mean value equal to the rated voltage of the plugs. On the latest engines the switching is sequenced between the plugs to give a uniform load on the system.

These are sophisticated engines - so no monkeying. The best way to test a low voltage glowplug is to connect it to the battery in-situ with a 21W stoplamp bulb in series with it. The bulb should light brightly initially then dim slightly as the plug heats up slightly. Don't take the plugs out of the engine unless definitely faulty - some have ceramic tips which may break off in the engine.

The in-built diagnostics will identify an o/c glowplug for you anyway. It's a pity the software designer knew nothing about engines - the glowplug identifiers in software are the reverse of the conventional cylinder numbers...

659.

Reply | Report as offensive | Link