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Old 23-01-2016, 15:27   #1
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Glow plug light will not go off

I have a MD2040, Volvo Penta, 40 hp and when I start the engine, the glow plug light will not go off. I took the wire off of the glow plug connection bar, not sure of the correct name, and cleaned it. I connected my volt meter and have11.59 v. At the wire right before the glow plugs? The manual says glow plug rated at 10V and system is 12v. I have a 12v system. Any suggestions as to what to check?

Until fixed, is there a problem running the engine as is?
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Old 23-01-2016, 15:53   #2
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Re: Glow plug light will not go off

No experience with Volvo, but on our Nanni, the glow plugs are controlled by a relay that in turn is controlled by the switch on the instrument panel. That relay, on our boat, has failed twice in 4000 hours. The switching is somewhat complex, so have a look at your wiring diagram. At any rate, the fact that there is 12 volts at the plug says that perhaps the relay is stuck, and for sure the plugs are still activated. I suspect that the engine will still run ok, but you are quite likely to burn out the plugs if run for long.

Disclaimer: I ain't no expert!!

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Old 23-01-2016, 15:57   #3
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Re: Glow plug light will not go off

One likely candidate is the ignition tumbler (you have a keyed ignition?). The return spring gets weak over time and does not push the key back from the glow plug position. Mine have been that way for years, Im just used to it and automatically bump the key back slightly after cranking (very slightly, like 1/8" ).

Its common for glow plugs to be rated slightly below system voltage so they heat up fast, but if they stay on you will burn up the glow plug.
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Old 23-01-2016, 16:05   #4
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Re: Glow plug light will not go off

Another "non expert" chiming in .

The above two posters are on the mark unless you have a timed system for the glow plugs.

You will have a stuck relay or a stuck ignition/start switch or a broken timer. The glow plugs will be controlled either by the ignition/start switch via a relay or by a timer via a relay.

And yes, while the engine will run just fine, the glow plugs will burn out much quicker if left on.
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Old 23-01-2016, 16:08   #5
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Re: Glow plug light will not go off

Yes I have a key and will check that. If that does not work and I can't readily find the problem, would there be a problem with putting in a connection at the glow plug wire and just disconnect after the engine is running? Would hate to burn up a plug and just add to my problems.


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Old 23-01-2016, 16:21   #6
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Re: Glow plug light will not go off

Wiggle the key in the ignition once the motor starts and see if it goes off. I know my ignition has a momentary on for the glowplugs that tends to stick and not release.

Glow plugs draw a lot of current. I wouldn't like to leave them powered up for any length of time.
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Old 23-01-2016, 16:22   #7
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Re: Glow plug light will not go off

Can you look at the last few pages of this manual and identify which instrument panel you have- A, B, or C? A&B are pretty much the same except A doesn't have the key switch.

You should be able to click on this link, it is 4.7 mb:

Redirect Notice

The wiring diagrams are at the end, pages 14-20
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Old 23-01-2016, 17:22   #8
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Re: Glow plug light will not go off

I have a D


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Old 23-01-2016, 17:26   #9
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Re: Glow plug light will not go off

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Originally Posted by landonshaw View Post
Yes I have a key and will check that. If that does not work and I can't readily find the problem, would there be a problem with putting in a connection at the glow plug wire and just disconnect after the engine is running? Would hate to burn up a plug and just add to my problems.


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You could just install a switch, but personally I would rather confirm the source of the problem...could just be a symptom of something else like a short in the wiring harness...not an uncommon problem either.
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Old 23-01-2016, 19:07   #10
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Re: Glow plug light will not go off

I agree. I will put in a switch but only until I find the problem. I will let you know tomorrow how it goes.


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Old 23-01-2016, 20:51   #11
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Re: Glow plug light will not go off

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Originally Posted by landonshaw View Post
I have a D

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Is your glow plug light on the panel all by itself or is it located in a block of 4 lamps, along with temp, oil, and battery?

They are wired slightly differently.
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Old 24-01-2016, 04:21   #12
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Re: Glow plug light will not go off

Mine is in a set of 4 indicator lamps just above the key. The glow plug light is the last to the right.


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Old 24-01-2016, 06:59   #13
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Re: Glow plug light will not go off

As already mentioned it could be that your ignition switch is not returning cleanly to the "run" position and slightly hanging up in "glow". If that's not the problem, the next place to look is the glow plug control relay. The black box mounted on the port side of the heat exchanger/exhaust manifold contains two relays, one for the starter and the other for the glow plugs. The glow plug relay is probably failing and staying closed.

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Old 24-01-2016, 08:39   #14
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Re: Glow plug light will not go off

Thank you the insight into the relay. Is there a way to test it?


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Old 24-01-2016, 08:42   #15
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Re: Glow plug light will not go off

I am guessing to take the relay out. Put 12v to it, disconnect and test for continuity. If there is a circuit after it has been activated, then it might be the problem.


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