I just bought a 2004 5.9 that won't start. I cant read the codes from the dash by turning the key, cant read the codes with a code reader (cant communicate with vehicle), the lift pump wont run with the key on or bumping the key (it does run with a jumper wire to the pump), I tried starting it with the FRP unplugged, the batteries are up and charged. It will turn over good but I dont think the ECM is coming on. Also the dash lights up but the Volt gauge shows 8 volts with the key on. The gauge test does work however.

 

almost sounds like the ecu disconnected from the truck somehow? i know a buddy of mine just had a similar issue and had the truck towed to a service center. they had to re-link the ecm to the truck and then the truck started just fine.

not sure if theres a way to test the ecu without towing?

 

Tonight I cleaned all the ground locations I could find, checked/swapped around all the relays and fuses, unplugged the fan clutch, cleaned the post going to the fuse box, unplugged and cleaned the 2 plugs behind the drivers fender well and still no go. When I crank the truck my gauges dont move...volts stays on the bottom 8v peg, fuel says its empty, tach doesn't move while cranking and oil pressure doesn't go up. The red theft light stays solid red. Is that correct? Also I am still unable to scan for codes or turn the key 3 times to get the codes. My scanner says "unable to connect to vehicle"
I don't know what else to try.

 

someone has to know if theres a way to check if the ecm disconnected from the truck somehow..

 

Tonight I checked the voltage at the fuel pump relay. It is only getting 6.4 volts at the relay. I wish I could find a diagram that showed the pins for power going to the ECM

 

is power coming out of the relay? or just to the relay?

 

[QUOTE=Gatorm;1082842My scanner says "unable to connect to vehicle"
I don't know what else to try.[/QUOTE]

Until you solve that problem it won't run. Either the ECU is dead or there is a bad connection on the data bus. That error tells you the ECU is not communicating.

 

No power coming out of the relay. There isn't enough voltage to trip it

In the morning I am going to unplug the ecm and check the (+) wires and make sure I have 12v coming in and back probe ground wires in the ECM plugs and see if they will light a test light

 

hopefully you dont end up forced to go to the stealership... but sounds like you may need a new ecm thats pre set up for your vin.. and then maybe you could go back to the truck plug it in and be ready to go.

i sent a text to my buddy but he hasnt gotten back to me about his issue.. he literally had the same issue and needed a new ecm as far as i remember. but again im trying to ask him to see what his was to hopefully help you more.