W210 Glow Plug Malfunction and Check Engine light - PeachParts Mercedes-Benz Forum

kolnerspieler · #1 10-20-2016, 11:11 PM

Hey Guys,

I was a very interesting problem. I keep getting a check engine light for a glow plug malfunction circuit. I have changed all 6 glow plugs about 2 months ago. I still had the problem and a hard time starting the car. Next I found that the wire harness was rubbing against a metal pieces and shorted some wires. I repaired this and then found the fuse to be broken on the glow plug relay. Replaced the strip fuse, but still had issues with starting the car. The next thing I did was replace the relay itself and have had no issues starting the car and no issues with the glow plugs, but I keep getting a check engine light.

I have also identified a pattern. When the car is cold and I want to start the car the glow plug coil light comes on and everything is ok. The car starts just fine and I get no check engine light. Now if I switch the car off and try starting it again the glow plug coils do not come on and after starting it I get a check engine light immediately. I clear the codes and the next day on the first try no issues and sometimes on the second try also ok, but if tried in short periods between glow cycles at some point the glow plug coil light does not come on and after the start causes a check engine light to come on.

I also figured out that running the glow cycle more than 1 time before staring that it will cause a check engine light to come on. so for example I put the key in run position and the coil light comes on, Then I take the key out and run the cycle again, but this time it either does not come on or comes on for a split second and then after starting the car the check engine light comes on.

I checked the glow plugs and all 6 are only a couple of months old and good. The relay is new also. Not sure what could be causing this to happen. Anyone have any ideas?

treetops · #2 10-21-2016, 08:34 AM

Not sure if it makes a difference in this case, but year of build is usually helpful. Sounds like you still have a short or bad connection in the harness. I just changed out one GP and noticed one GP plug on the harness has a broken-ish plug. Still works but the possibilty of the plug coming off the Gp is there.

jay_bob · #3 10-21-2016, 08:44 AM

Definitely confirm the wiring harness between the relay and plugs is secure.

Also the relay control is not like the older models, there is a 2 wire control connection. One wire is terminal 50 (the starter signal) and the other is a single wire PWM data connection to the ECU (this is is how it talks to the ECU to determine glow time, and communicate dead glow plugs). This terminal is rather flimsy and can be intermittent. Tjts1 had this problem with his glow relay, search for a thread from him on this.

The glow light does not get controlled by the glow relay, the ECU controls the glow light via CAN bus to the cluster. Far cry from the early 115 where the glow light was literally in series with the glow plugs.

Try pulling codes with an OBDII reader, there are 3 codes for glow plug failure, one is cyl. 1 or 2, another for cyl. 3 or 4, etc.

kolnerspieler · #4 10-22-2016, 10:48 PM

I took a look at the other posts and checked the glow plug relay connections. I have a slightly different set up. I do not have the 2 wire (one for ground and the other for CAN BUS). My relay has a connector for the glow plugs, a red power cable, and then a 6 pin smaller connector that has 5 leads. I checked all the connections and am still getting a check engine light. Tomorrow I will check the coolant temp sensor cables. The sensor itself is brand new, but I will double check the cables to make sure that they are ok.

I am not sure what else I can check on this.

ESchwab · #5 10-23-2016, 01:18 AM

Kolner, Treetops asked for the build year, and it's not in your post. I think the glow plug relay setup is not the same for all W210s. I have a '98 and noticed in a picture in a different thread that the '96 relay (maybe'97) is different from mine. I think that is the reason he asked for the build year.

jay_bob · #6 10-23-2016, 11:32 AM

Agreed, I forgot they made a huge amount of changes between 96 to 99 in the first gen 210, and the year does make a difference.

kolnerspieler · #7 10-24-2016, 09:59 AM

Hey Guys,

sorry I forgot to mention that. Mine is a 96. Looking at it online it looks like they had different versions between 96 and 99.

Let me know if anyone has any other ideas. I appreciate the help.