Just pull the plug for the wires to the GPs from the relay (Bigger
plug) Test resistance to ground from each socket in the plug. Should
be 0.7 ohms, but many multimeters will show around 1.2 to 1.4. Look for
anomalies amongst the 6 readings. Infinity = bad. Under 0.4 (if you
have a really good meter that can detect small fractions of an ohm)
means a plug going bad, which should also be replaced. If all 6 read
within 0.2 of each other, they are likely all good.
Jim and Philip say the only way to test for good is with a ammeter and
big wires. I've been successful always with just a cheap ohm meter.
But they are right, the BEST way to test is with an Ammeter.
After checking GPs, with the plug still off the relay, turn the key to
glow position (best done by a lovely scantily clad assistant) and check
the 6 pins on the relay for +12v to ground. While you are in there,
change the 80 amp fuse.
Floyd Thursby via Mercedes <mailto:email@example.com>
March 7, 2018 at 5:51 PM
This post from one of the forums is exactly what is going on now that
I cleaned up the EGR valve and got that sorted. Looks like a GPectomy
is in order, or at least test them and the relay before I tear into
them all. Max you said you had the stuff to deal with it?
First time starting after the manifold/EGR work took a bit of
cranking, but then it has started fine since. So either at the
beginning it was sorta dry from sitting, or the GPs weren't all
putting out. it did belch lots of smoke too, FWIW. But it will start
and run now so not a huge issue at the moment.
I am getting the following errors.
P0380---faulty glow plug relay
P1369---faulty glow plug
My questions is are both bad or is one causing the other? Each morning
the glow plug light functions properly for the first start but after
that it give the error each time. I hate to spend the money on a relay
if the plugs are the problem but I also hate to change the plugs if
its just the relay. Is there any way to know which it is or if it is
both? Would really like to fix this before winter sets in.
I have been down this road several times with my 99 E300-TD and, to my
mind, the only solution is to do whatever is necessary to prevent
future occurences. This is a very expensive, but necessary,
maintenance item. Approximately each 100k km I have experienced these
symptoms and have concluded that one or more glow plug is faulty.
Given the labour to remove and replace the glow plugs, I change all
six plugs, even though only one or two have failed. On the last visit,
at @ 300k km, the relay was found to be "intermittent" and was also
changed. This is about a $1000 proposition but, to my mind, cheaper
that the 3-4 major tune ups that an equivalent gasoline engine would
have required during the same 100km.
That is why I would check the resistance of the individual glow plugs
first! If they check out, then test the relay.
At first glance I can't see how the glow plug fault would fault the
relay. The relay is either on for a period of time and passes voltage
then off or it's always off or always on, both of the later create
faults. Good luck
the car computer can sense something wrong with the circuit, but can
not pinpoint the bad item. That what multimeter is for.
If the engine starts fine in the morning, that is indication at least
some plugs work, meaning the relay is good.
so if the relay tests fine it could be throwing the code only because
of the plugs or vice versa? just want to get an idea if i will
probably need to replace the relay no matter what or if there is a
chance it is ok and the plugs are just confusing it.
Those systems are fool proof. The relay is either open or closed,
voltage does not get to the glow plug(s) or regardless of key position
voltage is on and your battery drains.
You must test each glow plugs resistance, if they are low say 6-8 ohms
they are still good. Then test the voltage at the relay, with the key
in 0 and 2. If you get 12V with key at zero------whoooooooooooooops.
If you get 12V after car runs for three
The relay is about 150 bucks.
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