The issue reared its ugly head again today. Worked fine at startup (light went out after a few seconds but no buzzer) and stayed out the whole 35 mile trip. But, after sitting for 8 hours, I went to start the car and the glow plug light came on but never went out after a full minute. I started the car (started fine) and the light went out. Started driving and the light came on and would not go out unless I pulled over, shut the car off, and re-started. Even then, it would come right back on in less then a minute. Finally, I got out and pulled the connector off the glow plug relay (the big one that connects to the glow plugs themselves) After disconnecting the connector, the light would now only come on randomly for a few seconds, then go out instead of staying on constantly.

After letting the car cool I checked the system again. Just like a couple days ago, all the glow plugs ohm out fine and voltages check out good.

What the hell could be causing the issue??? The only difference I noticed is that this morning when the system worked fine, the outside temperature was about 40 degrees, and both times when it acted up, the outside temperature was about 60 degrees.

Help

Glenn

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2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)