So a few weeks ago when I started the E300D, the glow plug light came on and then went out as usual. Then once the car started (just fine BTW), the glow plug light and the check engine light came on and stayed on. This happened for a couple of weeks and then the glow plug light would go out but the check engine light stayed on. Then after a few more drives, both light stayed off as is normal.

I know that the glow plug light staying on typically indicates at least one bad glow plug. In my case I suspect only one bad glow plug, since the car starts nicely. I haven't had a chance to check them yet, but I certainly will. What caused the glow plug light and then also the check engine light to return to normal functioning? Did the bad glow plug fix itself? Did the car say to itself, "Well this idiot isn't going to check the glow plugs, so I may as well turn off the warning lights."

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Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles

did you diagnose read yours?

diagnosing a preglow system:


http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/605_606/15-4000.pdf

So I'm reviving this thread. All had been normal for almost six months. Then the other day the same thing happened. Both the glow plug light and the check engine light both came on and stayed on. After a few starts the glow plug light now behaves properly, but the check engine light is still on. I'm wondering if the check engine light stays on for a certain number or starts and then resets itself. I haven't pulled a code to see exactly what the check engine light is trying to tell me, but I did check the voltage to each glow plug and they all read around 0.7 v which is what they should read.

__________________
Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles

If there is an intermittent problem the check engine light will go off till the problem shows up again.
On US Cars you can scan the computer and see a possible source of the issue.

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84 300D, 82 Volvo 244Gl Diesel

Finally got around to checking OBD codes. Wasn't in a rush because the glow plug light and the check engine light were behaving properly and the car was running great. So as I was kind of expecting code P0380 was stored, indicating an issue in the glow plug system somewhere. As noted above, all the glow plugs tested fine, so it seems like I'm looking at an intermittent problem with a glow plug or the relay or something else? Input and suggestions welcome. I cleared the code and will see when/if it pops up again.

I'm not too worried about things, since it has happened maybe three times in the past two years or so and each time after awhile things go back to normal. I just did a B service. Car runs great. Temps are typically plenty warm enough to start with one or even two glow plugs misbehaving and I'm lucky if I drive the car every sixty days.

__________________
Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles

I would go ahead and do the plugs as you’re probably building up carbon on the plug that is not firing. It is not a bad job if you are prepared to have to drill one or more out.

I have the complete tool kit available for loan, if you want to have it on hand before you start.

OM606 glow plug change - one broke off

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Thanks for the reply jay_bob. I've changed the plugs a couple of times over the years. Had to drill one out once. I now make sure I do the job with the engine warm/hot and always use anti-seize on the new plugs. As little as I drive the car, I think I'm just going to let things ride unless things get worse. The job just isn't worth it to me at this time.

I don't have the kit you have, but I do have the correct tap, sockets, etc. to hopefully make things go smoothly. Thanks for the offer - I'll keep it in mind.

__________________
Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles