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Ecm not enabling glow pug turn on !

C

Craigb

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2004 h1 6.5td
the ecm is not enabling the yellow wire on the ca. Style glow plug controller .
I’ve replace ,relay controller , glow plugs , air in take sensor , coolant sensor , cleaned all grounds ,
I connected a light bulb to one on the glow plugs to see when they turn on .
I can activate them with the tech 2 scan tool .
There are no codes coming up . what am I missing ?
thanks
 
Welcome to the forum @Craigb

what is the ambient outdoor temp? and which glow plugs did you install? always bench test new ones before installing them. one thing you can do is trick the ecm into thinking it's -40 outside but disconnecting the ect sensor, key on and see what happens.

one thing to note is after the first initial key on cycle, you have to wait at minimum of 30 seconds with the key off to try again. also measure the resistance of each glow plug and it's wires up to the relay. if there is too much resistance the ecm will see this and shut them off.

with your tech 2, verify the readings of your sensors you replaced that they are accurate. also check to make sure all of your grounds are clean and good contact.
 
also check your fuses. when I first bought mine the glows did not work at all. I found there was a ECM fuse in the under hood box that was missing. the ecm still worked fine, read codes and all data, but apparently that fuse powered the portion of the glow plug system. of coarse mine is a 95 (obd1 system) yours will be different.

poor guy that I bought it from was useing a screw driver to light up the glows every time for over a year and didn't know why they quit working.
 
Funny story, when I bought my truck I drove out to the guys house to pick it up. while he was cleaning all his stuff out I was looking over everything. the glows, radio, dome lights, and AC didn't work. I had everything working before I pulled out of his driveway all just by installing missing fuses LOL. he was looking at me like WTF! all that never worked before. he didn't even know the AC had a charge in it.
 
I believe you have a coolant temp sensor that feeds temperature so the time the plugs cycle gets altered. Idk if a faulty sensor could have that affect or not.

I think the schematic is best alternative here for finding the cause.


If you need a simple solution to make them work in the mean time and to give you an option moving foreword: the bolt on relay sold by Leroy is a great option. You simply have a switch on your dash to it, and the little relay bypasses the factory unit forcing on the glow plugs. However the entire factory system is still in place and can operate normally by itself. https://leroydiesel.com/products/leroys-glow-plug-relay-override/
 
I did use this time delay relay on mine for a bit. until I was able to play with the tune on my ecm to get a couple of extra seconds out of my glows run time. the relay is programmable to any length of time. I played with the timing on mine finding that 8 seconds was the sweet spot using the AC Delco 60g glows. they require a little bit longer to warm up but are ones that have a limiting resistor built in to keep them from overheating and swelling up.

 
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