Background, I have had this car for about 5 years. I replaced the GP wire harness about 4 yrs ago, and the glowplugs about 1.5 yr ago.

About a month or so ago the GP indicator light started being erratic- not coming on when cold and then coming on for a short time until the motor warmed up. About a week ago it stopped working altogether and cold starts were very hard (temps in 30s at night).

I followed the tutorial on Diesel Giant and tested the glowplugs for continuity at the relay- found one was bad #5 cylinder. All other tests of the relay were fine- power at relay 11.8v and power to GP connector good on all cylinders at 11.6v.

Pulled the bad one last night, and put a new one in after I tested it for continuity and also put 12v on it and got nice red hot tip. Engine was still warm last night so I couldn't test it.

This AM I get up and try it- no GP light and hard start (42F ambient temp). Still get good current at relay and GP harness plug, and all GP test good for continuity between .4 and .7. Odd thing is that after starting up, the GP light on dashboard will come on for a short time.

Is it the relay? Did I miss anything?

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1995 E300 diesel

If relay tests OK....there is power to plugs, it sounds like you still have one or more bad glow plugs.

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-- Chris

'95 E300, 216k miles, Silver Surfer
'05 E320 CDI, 138k miles
'07 S550 4matic, 69k miles

Gone but not forgotten:

'76 300D, 350k miles?, SOLD in 1995
'75 240D, 300k miles, SOLD in 1991

but they all test ok for continuity at the harness plug - is it possible that one is still bad and that I must pull them all and individually test them?

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1995 E300 diesel

Can you hear the relay click off after the car is running for 90-120 seconds? If it's staying on or malfunctioning, it could be burning out your glow plugs.

Did you use Beru glow plugs or some other brand? Mercedes uses Beru at the factory. I've purposely destroyed several Bosch and Beru to see how much it takes to twist them apart. Berus are much stronger than other brands including Bosch.

Ohm meter check isn't as accurate as visually evaluating the glow color and glow location with the glow plug out of the head and directly connected to a battery via jumper cable.

You're luckier than most with this engine. Lots of owners bust one or two of the glow plugs removing them.

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900

I got Bosch from the local indy shop. Yes I can hear the relay click off.

Ug, so I guess I am removed the intake manifold and manually testing all of them.... glad I got a spare one.

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1995 E300 diesel

I would strongly recommend you ream the gp holes with the proper tool and clean the tapered part of the hole and the tapered part of the plug. I also strongly recommend you use Beru plugs and the Beru anti-sieze grease on the threads and torque to spec.

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900

what about just using an easy out as opposed to the method stated here?

PeachPartsWiki: Broken Glow Plug Removal

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1995 E300 diesel

I just tested the plugs for resistance, and they all passed including the one that is stuck so I think I am going to reinstall the others and just go with it for now.

Is it necessary to put a new intake manifold gasket on? the existing one looks fine.

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1995 E300 diesel

Easy Outs can expand the part you are trying to turn out and when the hole is small I have also seen Easy Outs snap off.
On the small items you don't know if the item is stuck beyond the strength of the Easy Out.

When and Easy Out snaps off it is even more difficult to deal with because Steel the Easy Out is made of is tough and hard.

However, there is a lot larger selection of Easy Outs these days then there used to be.

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84 300D, 82 Volvo 244Gl Diesel

OK so I decided to leave the stuck GP in there for now, since I don't have heat in my garage and its too damn cold to try and mess with it. I checked all the others that I had out, did resistance test and also put 12v to them to verify. I found one that passed the resistance test but didn't glow.

So I put them all back in, connected the GP wiring harness and tried the key to the on position but no GP light? There are 2 connectors that connect to the crossover pipe valve- I have not connected those yet because I still have the IM off to troubleshoot vacuum problems. Are these connectors necessary to the function of the GPs?

I have verified there is power to the relay and it is operating properly, confused as to why I don't get any glow with key on and cold (25F) conditions....

I am stuck until tomorrow because I was also removing the throttle linkage to lubricate it and broke one of the plastic ball sockets, waiting on new part.

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1995 E300 diesel

as connermn said - use that tool, I had a mechanic loan me a socket looking tool that actually worked like a slide hammer if I wanted to (he said it was for some chev diesel), but I used it in the same principle as the split nut tool. It literally pulled the plug straight out.

Get the engine really really really hot, I even removed the fan and attempted to loosen the plugs with the engine running. Engine temp was registering 105 (high spd electric kicked in) - They still squeaked. I did get them replaced - took me a whole day. Be sure to ream the holes and slather some copper antisieze on your new BERU plugs before you install them.

There are some crafty mechanics in some other countries who have made tools that are nothing more than correctly placed pilot holes for drilling etc for these glow plugs. They mount on the intake manifold bolt holes. if I can find a picture I will post it here.


precis - dont attempt OM606 glow plug service unless you have some tools like the split nut or similar to aide you, otherwise it has been known that people have trashed this engine because of GP failure.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

That GP light will now glow after start because one of the plugs is dud.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

so if even one GP is out, the light won't come on but the others will still work?

The issue I was having that started all this was extremely hard starts, and the light would occasionally come on after it was running.

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1995 E300 diesel

Yes.
The Glow Plug light does not control how long the Glow Plugs stay on. The Glow Plug Light is a prompt for the Driver (based on the under the Hood temp and a temp sensor inside of the Relay) and as you see has trouble shooting features.
So the Glow Plug Light trys to indicate to the Drive the minimum length of time needed for the Glow Plugs to be on; but it is the Drivers turning the Key that ends the Glow Plug Cycle till the Engine starts cranking.

If you ignore the light and leave the Key in the Pre-glow positon you will get about 30 seconds total of glowing before the timer shuts it off. Then when you turn the Key to start the Glow Plugs are agin turned on by way of a Wire that connects to the Starter Solenoid circuit.

On really cold days you can Pre-glow till the timer shuts it off and cycle the Key and Pre-glow for about another 30 seconds. You can do that over and over; the limiting factor is your Battery.

Another way to go is to plug in your Block Heater.

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84 300D, 82 Volvo 244Gl Diesel

Yes that is correct.

This is the indication of a GP circuit failure (its also written in the owners manual)

The system will work on the rest unless it was a dead short to ground.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)