[Vwdiesel] glow plug resistance

James Hansen jhsg at sasktel.net
Sun May 6 00:31:11 EDT 2007

I been a little busy, so sorry if this is too late.
THere are a few ways to test.

cycle the glow plugs three of four times with the engine completely 
cold, and shoot them with an infrared thermometer.  The good ones are 

As Stephen pointed out, a test light will work just fine.  With yours 
having isolated wires to each plug, hook the alligator clamp of your 
test light to the + battery post, and touch the tip to ground to check 
your test light. it should light up.  It does? good.  then touch the end 
to each glow plug wire, if there is continuity, the light will light. 
If the circuit is open, it won't.  Open is bad, meaning the plug is dead 
(the element no longer has continuity through the glow plug.  If you 
don't have isolated wires, you have to remove the bus bar first.

Another way is to pull the injectors and physically observe them in situ.

With a multimeter, set it to beep test continuity, and test each plug 
for continuity to ground.  Meter should beep when the plug is good 
(there is continuity) and not beep if they are bad.

Gee, there are a multitude of ways, mostly variations on a theme.

I suspect you couldn't get a consistent reading testing resistance, is 
your meter was too accurate, or too high a resolution.  You aren't 
looking for a resistor that is out of spec, you are looking for an open 
circuit.  They hardly ever fail closed (with continuity to ground), but 
it has happened, that's why the glow plug fuse.(which is another thing 
to check...)


raymond greeley wrote:
>   I understand just replacing old  with new, the labor is the killer, I 
> did that
> very thing with the daily driver. While changing them out i also 
> eleminated the buss bar so i could seperate each glow plug circut in 
> future diagnostics. certainly i can apply 12 volts to those out of the 
> engine
> how is it that i test the individual glow plugs while in the car.
>  I remember reading here that we measure resistance though i don't
> see a consistant measure when i do this. maybe my gauge is not woriking
> correctly or the connection is suspect.  
>  > Date: Thu, 3 May 2007 22:45:56 -0600
>  > From: jhsg at sasktel.net
>  > Subject: Re: [Vwdiesel] glow plug resistance
>  > To: rgreeley2 at hotmail.com
>  >
>  > give them 12v with a spare car battery or use jumper wires from your car
>  > battery. They get red. THe ones that don't are not good.
>  > If you have the motor out, just install new ones behind the injection
>  > pump. Yeah, I know, it seems silly when you have a handfull of them,
>  > but you'll understand when you're wrenching out the used one in a 
> month...
>  > -j
>  >
>  > raymond greeley wrote:
>  > > Hello All, Needing some info on checking the condition/resistance 
> of glow plugs. several are out of the
>  > > engine and I have an engine out of the car on a bench that
>  > > i would also like to test the glow plugs on along with testing 
> several other items before i install the engine. what kind of
>  > > ohms am i looking for as the archives are unclear or is there
>  > > another measure i should be testing for. thanks, ray
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