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WilliamR 11-04-2017 03:07 PM

Cummins pre-heater failure
Hello folks,

The pre-heater on my 2001 Cummins 5.9 BTA has stopped working. :confused:

Its the standard unit mounted on the top of the aftercooler. This one also has the manual override switch wired in (as per Seaboard Marine's site: ).

I want to get the unit working again even though I have an oil-pan heater also, as we anchor a lot and I can't use the oil pan heater all the time when on the hook.

The switch and light on the dash comes on when pressed, but I get no voltage drop like I used to. I have also pulled the unit and checked the unit out with a multimeter, as per the cummins manual. All the connections seem good, but I am getting no power to it when switched on (even with the temperature sensor disconnected). I wondered if it could be the solenoid, or if its simpler to just swap the whole thing out (and how difficut that is) to save hours of troubleshooting.

Any suggestions welcome.


The Other Gary 11-04-2017 03:33 PM

The usual fail is the magnetic switch and there are two of them on the port side of the block about half way down. They are mounted on a plate along with the ECM that almost never fails.
Buy several replacements as the same magnetic switch is also used for your starter motor mounted at the same height a few inches back.

Replace only one at a time as one is mounted right side up and the other upside down (don't ask me why) to get the wiring correct.

Having a spare pair in your tool chest means being able to repair the preheaters and starter if they fail, and they will.

Aquabelle 11-04-2017 06:00 PM

There is also a fuse in the pre-heater circuit....I suppose you checked that?

The Other Gary 11-04-2017 06:13 PM

He has replaced the fuse with the dash switch, of course the switch wiring could be off at the fuse holder.

WilliamR 11-04-2017 06:57 PM

Yep checked the fuse and wiring, thanks. But the solenoids are going to get a closer look. :-)


Ski in NC 11-05-2017 07:24 AM

If batt volts is on the low side, I think the controller won't energize the heater. The controller can do weird stuff. I took it off my 450.

Xsbank 11-05-2017 03:24 PM

Lots of Cummins owners disable the preheater as it is very hard on the alternator. Try starting and running yours without it to see if you still think it needs to be fixed?

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