Hello All,

Last Monday the glow plug light indicator in my 240D was out. As a result, the engine would not crank up. The glow plug light indicator was out for a few days. I changed fuse 14, but it did not make any difference. Then Thursday, I put the key in the ignition switch, and the light was on, and I was able to start the engine. Went to Autozone, had the battery and alternator checked. Both are functioning properly. I then checked all four glow plugs and the connector in the glow plug timer relay with the multimeter. Everything is working properly. (Battery, alternator, glow plugs, and time relay have been replaced in the last three years).

Any idea what could have caused the glow plug light indicator to go out (and making it impossible the start the engine)? Since it happened "out of the blue", I fear it may happen again. The car runs great otherwise!

Thanks for any suggestion.

Jack

Owned 240D Manual Transmission 1981 (2000-2009)
240D 1982 Manual Transmission (2008 - on)

 

Great! Thanks for the explanation and wiring diagram.
Jack

 

240d 1982 manual


The glow plug light comes on intermittently, car starts properly each time (well it is summer). I disconnected the glow plug wires and checked the voltage drop on negative battery terminal and also across the relay wire and the glow plug, turned on the igntion w/o cranking. All the voltage came up to about 11.75, but I notice the when I disconnect the first wire nearest the radiator and turned on the ignition and the light went on. All other disconnected glow plugs the light did not come on. Does this mean the first glow plug is bad or the rest of them are bad?

 

Check each of your glow plugs with an ohm meter, the readings should be 0 to .02 ohms. Also you need to check all of your wiring, and connections intermitant light indicates glow plug failing or poor connections.

 

The Glow Plug Light will act funny if one of more Glow Plugs has an issue.
So if one Glow Plug was not connected you created an issue that would have an effect on the Glow Plug light.

Checking the Glow Plugs with the Ohm Meter is one of the ways to check them.
Another way is to remove them and get one Jumper Cable and check them direct on the Battery.
A good one will get yellow hot at the TIP first in about 2-3 seconds.
If the Glow Plug gets hot in the middle first it is no good (this is an example of a bad Glow Plug that would pass the Ohm Meter test).

When the Glow Plugs are out it is a good time to clean the Carbon out of the Glow Plug Holes with a Glow Plug Reamer or some alternative method.

On some models the Glow Plug Relay is connected to a Temperature Sensor on the Cylinder Head. To the best of my knowledge the Temp Sensor only has an effect on how long the Glow Plug light stays on. But, a loose connection of bad Sensor could effect the Light oddly.

When My Glow Plugs were working intermittently. What I found out was that the Strip Fuse in the Glow Plug Relay was cracked (not burned).