Thanks, NYTDI! I was looking for that function under "Search", silly me!
Anyway here's my rambling piece from last fall:
Guys, I've been through all of this.
First I should repost as to how the ECU measures current: The GP relay uses a shunt circuit (an inline resistor,
as Brian correctly put it, across which it measures voltage). It measures two pairs of glow plugs at the same
time.
My MIL came on back in April. First I thought it to be a bad glow plug, so I changed them all. No dice; after
resetting, the MIL came on again a couple of days later. I checked every single connection from the battery to
the relay to the glow plugs.
FYI, there is a connection in the harness in the wiring duct under the airbox. This is between the relay and the
glow plugs.
I measured for voltage at the GPs, and all seemed okay. The car started just fine as well, even below freezing
temps. Next step was wasting my money on a new relay. Wasting is the key word here, don't buy one! Lastly, I
purchased a new harness a few weeks ago, and guess what, the problem is solved! The least expensive and
fastest to install part seems to be the first one to try, if your GPs measure okay!
I performed a post mortem on the old harness today by cutting it in half lengthwise. It's actually a
multi-layered moulding. The insulation of one of the feed wires was cracked right at the point where it enters
the flex-joint on the end of the harness, but no corrosion or broken conductors were found. There are two
high-quality crimp connections (both okay) in the harness to split a wire off to each pair of plugs. The wires are
crimped onto the GP connection terminals, and again, these were fine. Basically, I could find no real problem
with the harness at all, but a new one cured my returning code!
The terminals themselves are two-layer, the outer part being the crimp connector and main housing, and a thin
springy band that fits inside, to give extra "grip" to the GP's terminal. These are surrounded by a hard plastic
housing that doesn't have any "give" so the problem is not the moulding giving way and the terminal losing
tension. Examination of the inside of the terminals showed no sign of corrosion either. My only guess (I work in
the electrical field) is that the problem lies with the small thin inner ring that is supposed to give extra tension
onto the GPs. Since the surface area is large, minor oxidization could cause a fluctuating current that the ECU
could pick up as a problem. Remember, there are 20 Amps flowing through each connector, at only 12 volts. An
extra 0.1 Ohms of resistance would cause approximately 3 Amps less current flowing to a glow plug! From what
I've gathered, all of these faults are nuisance faults, that is, nobody has actually had a starting problem
(unless they actually have a bad plug). The factory parameters that VW set to generate a fault code may be
too strict, that is, they allow for a very small current variation.
To anyone coming to the Toronto GTG on the 30th, I'll bring my disected harness.
[ November 10, 2002, 17:03: Message edited by: Cosmic Green ]
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