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How cold is it where you are. If warm the circuit will only stay energized briefly. How are you checking the voltage? Check each of the studs to ground not across the relay. You should see 12 volts on the Large Power Feed to ground but key does not have to be on. Should see 12 volts on the small Control power post with key on. Should see 12 volts when checking the Glow plug feed circuit stud to ground with the Key on but again only as long as the PCM keeps the circuit energized. This is variable based on temps. If you have 12 volts on control and Power feed feed studs and no joy on the glow plug feed stud then use a jumper and ground the small lug on the relay that's toward the back of the truck. This is the post that the PCM grounds to energize the relay. If you ground it and the relay closes then the PCM is not sending the ground signal.
Test light then voltmeter. So battery term is 12.xx and then the small studs are the same. has brand new pcm. now the gp side was .07 and it's about 30 today but i had the truck plugged in when i swapped the relays. but it's at 60ish EOT and it's not plugged in. when i turn the key to on everything powers but the GP side stays cold.
Not a bad ground, the PCM is not sending the ground signal for some reason. Check to make sure the wiring is good to the PCM. If it is then it gets a little more complicated. Is it the PCM that's bad? Is it one of the sensors the PCM uses to determine if glow plugs need to be on? I don't remember what exactly it's looking at, Oil temp, ambient temp? Hopefully one of our members who knows can join in.
Some people who have had a similar problem have just added a switch in the cab and turned the Glow plug system into a manual operation. Switch on-ground provided, switch off- no ground. I guess you could get fancy and add a timer so you just push a button and it goes through a cycle. Then you don't have to worry about forgetting to turn it off and burning out your plugs or draining the battery.
It’s a brand new PCM like a month old PCM to my knowledge the botl to connect the truck to the pcm is firmly set. I had a switch already. Trying to not have one
If it was me I would get a wiring diagram and an ohm meter and make sure there is not a break in the wire from the PCM to the relay. If that's ok then research what the PCM is looking at to determine if glow plugs are needed. Then start checking to make sure those sensors are working and that the wiring to them is good.
Is this new PCM the same part number as the old one? Why did you replace it?
If it was me I would get a wiring diagram and an ohm meter and make sure there is not a break in the wire from the PCM to the relay. If that's ok then research what the PCM is looking at to determine if glow plugs are needed. Then start checking to make sure those sensors are working and that the wiring to them is good.
Is this new PCM the same part number as the old one? Why did you replace it?
How i test with the ohm meter (never did it before)
New PCM is exact same part number and everything and because my old one was bad
How i test with the ohm meter (never did it before)
New PCM is exact same part number and everything and because my old one was bad
I agree with Paul, Likely a broken wire, since most occur in the engine harness I’d start by checking from the 42 pin valve cover. If the ohm meter reads “OL” you have a broken wire.
for the Ground it is circuit 1086 from the valve cover connector is pin #13 and from the PCM it is pin #101.
tried to upload photos showing the PIN numbers but FTE is being wonky... maybe you can google it or I’ll try to upload later
12-08-2018, 01:54 PM
