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Originally Posted by treiberg
Back to this issue again. Car has been running fine for several months, with only a few times where light wouldn't come on, but usually if we just waited an hour or two, we would finally get the glow plug light and then car would fire up. But now I cannot get glow plug light on and engine will not start without it. Here is a tally of what I have investigated:
-glow plug resistance appears to be fine, all in the 0.6 to 0.8 ohm range
-glow plug relay seems to be fine, at least I see it providing 12V to output blades when I energize it, and you can hear relay click
-replaced the K40 relay
-problem appears to be worse when engine or ambient is hot
The problem appears to be that the signal to energize the relay is not working. I cannot consistently get 12v at the two input wires to the glow plug relay. My understanding is that this starts with the ignition switch, but it is also enabled by the temperature sensor located under the manifold. I wonder if this sensor has gone bad...??
Also, I need to start the car to move it. So I figured if I just apply 12V to the input side of the glow plug relay, then it will pass power to the glow plugs and I will be able to start it after 10-15 seconds - sort of bypassing the electronics that send the 12v. However, when I do this the relay only pops on for 1-2 seconds and turns right back off again, not nearly enough time to energize those plugs to allow me to start. Is that relay somehow super smart and know that my 12v is different than the one from the ECU?
If anyone out there has some input, or can even provide a wiring diagram for a 97 E210 E300D, that would really help.
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I went through this exact issue with my 97 a couple of weeks ago. First of all trying to hot wire the GP relay is not going to work because this GP relay is digitally controlled by the engine computer. Even if you manage to hotwire it, the computer won't allow fuel to the IP if it doesn't have clear communication with the GP relay. The GP relay has a PIC16 micro controller in it. There is a small 2 wire (3 pin) plug on the GP relay with a white and brown wire. Brown is ground and white is a data line from the engine computer. Grab that plug and wiggle it a bit. You'll see it has some play. The plug is poorly designed and intermittently cuts the data signal between the engine computer and GP relay.
The solution is fairly simple. Solder your own wires to pins 1 and 2 of the 3 pin plug on the GP relay and use standard off the shelf plugs to securely plug it into the car's wiring harness (brown and white wires). Leave everything else the same. You will also need to connect to the OBD2 port and delete the stored code (P0380 i think).
Heres an older thread where we discussed the issue and the fix.
GP relay help - 1997 E300 om606.912
My car went from intermittent no start to totally reliable starts after this modification. MB issued a service bulletin about this very issue.
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SUBJECT: DEALER TECHNICAL BULLETIN 31/98
31/98-1 RECALLS AND SERVICE CAMPAIGNS: WHEN REPAIRING ANY VEHICLE, ALWAYS CHECK THE VEHICLE MASTER INQUIRY FOR OPEN CAMPAIGNS
31/98-3 GROUP 07 - ALL DIESELS AS OF MY 96 (210.020, 210.025): For conditions of code P1482 (preglow control module) in engine ECU, in addition to the tests outlined in Diagnostic Manual 1.1 and 1.2, please check the electrical line and connectors between the preglow control module and the engine ECU (signal wire / ground and voltage supply) for possible intermittent contact, open contact, short to ground and / or power. If all checks OK, replace preglow control module. These additional tests are necessary to obtain a more precise definition of code P1482. In case of warranty, please use Damage Code according to identified problem.
H. Polz, Service Engineering
HPdg 12-18-98
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