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Discussion Starter · #1 ·
I have a 2016 RAM 3500 Promaster where the fuel pump relay occasionally gives out.
Sometimes while driving. Which is always unexpected and can be dangerous.
Usually, I pull over and wiggle it, or re-set it, or transfer one of the similar relays from the power distribution box to it's slot. This usually works, but is super annoying. My mechanic actually put in a whole new power distribution box, so I have the old one in the truck with all the fuses and other relays as spares. But it's interesting that this has happend with both PDB boxes. The old and the new. In fact, he told me that the one he replaced was stamped as a 2018 part, which indicated it had been replaced before, as the truck is a 2016. I've been to forums, but not seen this reported as a big time problem for the Promaster series. Anyway, I was wondering if you anyone has created a fuel pump relay by-pass for this Ram model. Thank you. Any light anyone can shed on this would be apppreciated.
 

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2018 136 HR Ont.
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...fuel pump relay by-pass for this Ram model. Thank you. Any light anyone can shed on this would be apppreciated.
I've rigged up a few switches to by pass pump relays on other vehicles, basically a switch, two wires with spades plugged into the PDB.

If I was you I'd be looking at other components than the relay and box. You might have a ground or power connection issue between the relay/chassis and the pump. Maybe the pump is defective?
 

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Discussion Starter · #3 ·
I've rigged up a few switches to by pass pump relays on other vehicles, basically a switch, two wires with spades plugged into the PDB.

If I was you I'd be looking at other components than the relay and box. You might have a ground or power connection issue between the relay/chassis and the pump. Maybe the pump is defective?
Hey, thanks for the feedback. So, if I rigged up a switch, and it worked (never failing again), that would be the end of it. But if it did happen again, that would lend credence to the other issues you mention. So let me ask you, when you rig up a switch, is it something you manually turn on when you get in the vehicle for a drive, and then something you need to turn off so the pump does not continue to run when you are stopped? If so, the next question is, with the four prong set up, what would the wiring typically look like? Would I litterally only be concerned with two of the four terminals? Just completing a basic circuit? And is it just a simple toggle switch you have used in the past? Again, thank you!
 

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So, if I rigged up a switch, and it worked...
I don't actually recommend using a switch but it can work.
You would need to turn it on every time you start the engine and every time you turn it off. It's easy to forget.
I'm kind of a gearhead so it was easy for me but if you're not in tune with all the little nuances and sounds of your van you might not want to do it.
The vehicles I used a switch on were 80's so less sophisticated engine management. I can't ever say for sure it will work although I suspect it would. BTW I use an old 120v light switch.
 

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'16 2500 159 HT Granite Window - OH(io)
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As 83Grumman stated, there is more involved with the fuel pump than just the relay. See attached diagram.
I believe that the "Fuel Heater Shutoff Switch" is mislabeled. "Fuel Pump Shutoff Switch" is probably a better description.
It combines signals from the BCM and the Powertrain Control Module. What generates those signals is anybody's guess.

Rectangle Font Parallel Slope Pattern
 

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Discussion Starter · #6 ·
Thank you so much for taking the time to find and forward that. This seems possibly out of the league of many typical mechanics (including probably at the dealers)
Are there electrical oriented places I would bring the truck with all this input?
One note. This typically happens after the truck has been idle for awhile (like two weeks to a month).
It will start normally and drive, but then, usually during that first drive cycle, or at the end of that first drive, this problem presents itself.
Think it's worth replacing the fuel heater shutoff swich? It seems to be right smack in the thick of things.
 

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Thank you so much for taking the time to find and forward that.
Think it's worth replacing the fuel heater shutoff swich? It seems to be right smack in the thick of things.
You are welcome, glad to help out.
The shutoff switch is also an impact detector, so it has mechanical parts. Very possible that it could be intermittent.
 

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Discussion Starter · #10 ·
The other thing I forgot to mention, is that when this first happened, about a year ago, my mechanic said that the code thrown was the fuel pump relay.
As mentioned, it's probably happened 3 or 4 times since then (only once while actually driving). The other times it was stopped and just wouldn't re-start.
Each time I played with the relays on the power distibution box. Each time it worked and the vehicle could restart and drive.
I pretty much now know what each of the relays in that box control. Sometimes I just unplug the fuel pump relay an re-set it.
Other times I have replaced (swapped) relays. I have an OBD scanner and the Fusion app. If it happens again, before I play with it, will that app tell me whether it's the
relay, fuel pump shut off switch, BCM or PCM? Any thoughts? Also, I'm assuming that power distribution box has a harness or two underneath it that plug into it. Could the wire in the harness, that connects to the fuel pump relay, be making an intemittent connection just below the distribution box - in the harness itself. Do you know if that harness is an item tha can be replaced?
Thank you.
 

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I don't think the OBD code will be that specific. Find out where the fuel shut off switch is. If it happens again don't do anything except rap on the fuel shut off switch box and see it that gets the pump going again.

It might be a good idea to go the the fuel shut off switch and pull/pull the connector off and on a few times to make sure it has a good connection.
 

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@LarryK
That's a great diagram for anyone looking for a engine running signal. Nice to see the fuel pump is on a 30A fuse.
One could use the "Fuel Pump Rly Ctrl" coming from the Shut-Off Switch (blue wire in my diagram) to control a separate relay for engine running needs. Good idea!
According to wiring diagram, find it at C5 pin 11 of the underhood Power Distribution Center (PDC)
 

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One could use the "Fuel Pump Rly Ctrl" coming from the Shut-Off Switch (blue wire in my diagram) to control a separate relay for engine running needs. Good idea!
I would prefer to tap into the gray wire because it is in a circuit that is fused at 30A. If a relay took .5A from that circuit you only add 1/60th load compared to what the circuit is fused for. I don't like to chance tapping into or adding loads to any BCM circuits.

Based on the diagram, doesn't it look like the blue wire (terminal 86) grounds the coil of the FPR relay with the positive (terminal 85) coming from fuse 16?
 

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I would prefer to tap into the gray wire because it is in a circuit that is fused at 30A. If a relay took .5A from that circuit you only add 1/60th load compared to what the circuit is fused for. I don't like to chance tapping into or adding loads to any BCM circuits.

Based on the diagram, doesn't it look like the blue wire (terminal 86) grounds the coil of the FPR relay with the positive (terminal 85) coming from fuse 16?
You are correct Sir. Being that the blue wire is a ground path from the BCM, the current may be monitored by said BCM, and cause a fault code if additional load (the new relay coil) is added.
Think I OD'd on turkey yesterday. :)
 
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