[Vwdiesel] FIXED: Dying Glow Plug Relays

Roger Brown r.c.brown at ieee.org
Mon Aug 15 17:07:11 EDT 2005

paulr wrote:
> Hi all,
> A followup to my post about "dying" glow plug
> relays from last week.
> To recap, a new glow plug relay I installed
> quit in 3 weeks. A warranty replacement quit
> again 3 weeks after that.
> I tested the second relay in the car, with the
> Vag-Com "output test" function.  The "bad" glow
> plug relay could be made to click on and off and
> draw current.
> I replaced the engine coolant temperature sensor.
> The glow plug relay that was "dead" began working
> fine on its own. The car idles smoother and seems
> easier to start now.  Noticed some improvement in
> driveability too.
> The coolant sensor never gave a fault code. It
> only seemed to make the glow plug relay act up.

I observed the same thing with my old style relay tester.  I had a drawer full of "bad" relays and all of them worked fine given 
reasonable temperature sender resistance inputs.  All the "bad" ones did act up when given unreasonable inputs like excessively 
high or low resistance.  My "good" relays seemed to tolerate the out of spec inputs and "do the right thing", regardless.


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