rogerdckwrth1

Hi, I need some help after a week of trouble shooting. 2009 E320 Bluetec US Specs. 90k miles. Got the code 0672 and replaced the #2 glow plug and cleared the codes. But, got same code with the glow plug light coming on with ignition on, going off, and then coming on for a short amount of time depending on how warm the engine was. I did more troubleshooting and switched the #4 and #2 glow plugs. Still got the same indications and code of 0672. I took voltage readings to compare #4 and #2 circuit and all reading were the same (ignition on 5V, engine running cool 9V). I then got codes of 0672 and 0674 because both connectors were off with the engine running. I reset the DTC and after two starts, got only the 0642 code. So I suspect the glow output stage even though there is no voltage indication of a problem. I am using a good DTC tester capable of reading and erasing the codes but I also wonder if there is a stored code hidden somewhere where a generic will not erase. Any help would be appreciated. The car runs great and the only reason I will need to fix it is the annual emissions test.

Plutoe

With all your reading, I am amazed that you did not see where glow plugs are tested based upon their resistance(cold) not voltage---I know ohms law, however just adjust your meter.

There isn't a glow plug control module(fault storage),the ECU is controlling the glow plug timing and that is where the faults are stored.

Depending on the tool used will enable the degree of testing. As an example there are about four guided glow plug tests, including wiring that I can do with DAS Xentry to quickly determine the issue---you can't do that and are left to hunt and peck at which component is faulty-------------my suggestion is get a good scan, because those components are expensive and scans are cheap!!

apl175

So i had a similar issue that I wrote about before. I was getting glow-plug indicator light on when engine was hot, and at idle, along with a Check Engine. Sometimes it would be the glow-plug light only, and sometimes it would go away on its own.

I don't have the P error code, but it was DAS Fault Code 2942-004 "Glow Plug 1 Idle Speed", which apparently indicates a fault in plug #1, when the CDI Engine Control Unit requests glowing when the engine is at idle and hot.

I measured resistance at the connector to this glow plug and found the resistance to be the same, hot, cold, both when the Glow-plug light was showing a fault, and normally. Found the resistance to be the same (all under 1 Ohm) at all times, which indicates the glow plug is probably OK.

DAS guided tests were to manually measure the resistance at the connector for all glow plugs and note any differences or resistance above 1 Ohm. There was also some other automated DAS test, that does activate all glow-plugs, but this passed without error even with the fault being present.

Replaced Glow-Plug Output Stage, and the problem has not reoccurred.

rogerdckwrth1

Yes, I am thinking glow plug output stage also. I tested the glow plugs for resistance at the beginning of the problem and they tested .3 ohms. I did a voltage test on the connector and throughout the cycle, the voltage on 2 and 4 remained the same--starting at 9v and going down to 5V as the engine warmed. So, the glow plug works, there is voltage going to #2 the same as #4, but I keep getting the 0672 fault so the problem must be in the GPOS getting a false sensing. Just for the fun of it, i hooked the new and old GP to a 12V battery and they both heated the same. Well, I guess I know have a good spare NGK GP! I have a good tester and will now delve into how to test the GPOS with it. Thanks

apl175

Bad Bad Bad - NEVER ever do this to test or activate glowplugs for the OM642 engine. These glow plugs are not designed to take 12 volts directly from the battery.

Service literature says that "...12 volts can quickly destroy the glow plugs. They must only be functionally tested using the Diagnosis Assistance System (DAS)...a dropped, stressed or suspected damaged glow plug must never be placed in to operation. Hairline cracks may develop which may not be immediately visible, such cracks may cause the ceramic insulator to separate while in situ causing possible engine damage" (paraphrasing from memory).

rogerdckwrth1

Thanks. Good info and will not do it again. Luckily I applied it for about 2 seconds and shut down just as they started to glow. I wanted to compare how long that took between the new one and the suspected bad one. The new one is now in #4 and is working fine. Better to be lucky than smart but I might have trouble down the road.

rogerdckwrth1

Can anyone suggest a good place to buy Mercedes parts on line? Dealer wants 180 for the glow plug output stage. Roger

apl175

$129 + shipping at parts.com which is fulfilled by an actual MB dealership.
Search for the part by number, get rid of the letter at the beginning of the part # when searching.

rogerdckwrth1

Glowplug output stage was bad. Replaced it and reset and all light out! Remember, only indication was a check engine light and a code of 0672 indicating a problem with the #2 glow plug. If this happens to you, before you buy a glow plug, swap the indicated bad one with a known good one (#4 is easy to get to if it is good). Reset and see if that fixes the problem or migrates the problem to the swapped cyl. If it migrates, glow plug is bad, If the problem stays with the initial cyliner, I suggest the problem is in the GOS. Good luck and thanks for all of the assistance.