2004 Ranger no communication with ecm

[jalex2001]

have a 2004 ranger 4.0 cant communicate with ecm... Ive checked all fuses and checked the obd2 plug. Truck will not start/turn over.

 

[ShhhhhDougsHere]

You said you checked all the fuses.
What about the relays?

 

[lil_Blue_Ford]

I’d try replacing the fuse for the cigarette lighter just for giggles. Wouldn’t be the first time that solved a problem with a “good” fuse. I still haven’t figured out how that works though.

Other than that… wiring problem maybe? Maybe the main fuse is blown (engine compartment, under a cover on the engine side of the fuse box)? Maybe the capacitors in the computer let go (granted, yours is a little new yet for this problem but it’s possible)? Might have to get into the weeds and start testing wires to see what happened.

One other thought, what do your main battery grounds look like? I’ve had them go bad inside the insulation, I only figured it out by flexing the wire and hearing a crunchy sound. Skinned back the insulation and it was corroded to junk. Was causing all sorts of crazy issues just because the ground was bad. I build my own out of 4 gauge welding cable now at either the first hint of an electrical problem or I get the opportunity (like when I had to swap the motor in my 92, I’m already right there and I had to disconnect it anyway). I make sure to use dielectric grease or no-alox (hardware store, electrical section, electrically conductive anti-corrosion stuff they use on aluminum wires, dielectric is not electrically conductive).

 

[jalex2001]

ok found the problem.... shorted alternator! communicating now but the truck still will not start. i can short the starter relay and it will turn over but will not start. any suggestions? no security light on or flashing.

 

[ShhhhhDougsHere]

I hate to be a stickler but if it's still not starting you haven't found all of the problem.
You found part of the problem but not all of the problem.

And on top of that My first question has not been answered yet.
So I will ask again.

You said you checked all the fuses but what about the relays?

 

[jalex2001]

I hate to be a stickler but if it's still not starting you haven't found all of the problem.
You found part of the problem but not all of the problem.

And on top of that My first question has not been answered yet.
So I will ask again.

You said you checked all the fuses but what about the relays?

yes all fuses and relays checked good! Almost acts like the Pats has it shut down but like i said no security light are on. Also no spark from coil pack. I can hear the fuel pump running too

 

[ShhhhhDougsHere]

Okay you now said that fuses and relays are all checking out good.
That's great.

Now you've also states if you can short the starter relay it will crank over for you.

If you take the starter relay out and test the wire clips ( I don't think wire clips is the right wording but hopefully you still understand ) that the relay plugs into with the key on do you get 2 ( hot ) power wires, 1 ground wire and the wire that goes down to the starter?

 

[jalex2001]

Okay you now said that fuses and relays are all checking out good.
That's great.

Now you've also states if you can short the starter relay it will crank over for you.

If you take the starter relay out and test the wire clips ( I don't think wire clips is the right wording but hopefully you still understand ) that the relay plugs into with the key on do you get 2 ( hot ) power wires, 1 ground wire and the wire that goes down to the starter?

Only 1 wire is hot 12v can jump 12v with my power probe and get the starter to turn over. Have a brown wire that is 12v yellow to starter. Then 2 18 gauge wires yellow w/red and blk/red that dont seem to do anything. Ive applied 12v to each with power probe and checked them for ground.
Shouldn't one of those wires come from the pcm? and one go to the neutral safety switch?

 

[ShhhhhDougsHere]

If you have a 4 pin relay.
Unless I'm wrong when you have the key in the on position you should have 2 hot wires
( 1. That's hot all the time which means it will be hot even if the key is in the off position. )
[ And 1. that the key being turned on makes hot. ]
Then you should have 1 wire that is a ground wire.
The last wire goes to the starter.

 

[ShhhhhDougsHere]

Wait I'm wrong the second hot wire should only be hot when the key is in the start position.

 

[ShhhhhDougsHere]

For a 4 pin relay.
The way the relay works is the wire that's hot all the time and the ground wire makes the relay hot and ready to be used.
Then once you turn the key to the start position the 2nd hot wire then becomes hot and clicks the relay over sending power from the 1st hot wire to the starter.

 

[jalex2001]

Wait I'm wrong the second hot wire should only be hot when the key is in the start position.

But dont the pcm have to take a neg and turn to postive? Thats what ive been reading. I dont know....

 

[ShhhhhDougsHere]

If my explanation on how I relay really works, is wrong someone please feel free to correct me.

 

[ShhhhhDougsHere]

I will ask someone who I'm sure know for positive.

It may take him a little bit to reply however so please bear with us.

It's this easy @Curious Hound please read this thread and help this man.

 

[jalex2001]

For a 4 pin relay.
The way the relay works is the wire that's hot all the time and the ground wire makes the relay hot and ready to be used.
Then once you turn the key to the start position the 2nd hot wire then becomes hot and clicks the relay over sending power from the 1st hot wire to the starter.

If my explanation on how I relay really works, is wrong someone please feel free to correct me.

Im familiar with relays I install remote starts all the time but this Ranger has me puzzled. Ive got the wiring harness completely out of the loom and Ive ohmed wires most of the day. I havent found anything shorted or broken.
Bought this truck not running so trying to get running to sell.