Sounds like s good plan. 

Sent from iPhone

> On Mar 7, 2018, at 7:11 PM, Curley McLain via Mercedes 
> <> wrote:
> 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 <>
>> 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.
>> --FT
>> 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 minutes--------------whoooooooooooooops.
>> The relay is about 150 bucks.
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