Ok long story I pulled truck in the shop a year ago an pulled engine it was running at the time. It broke #7 oil ring so rebuilt engine an just now getting it set back in. Got all together an went to fire truck up an its not reading ecm so hooked up scan tool an can read all but ecm. Checked fuse at fuse block an all fuse is good checked plugs an pins on ecm an all look good. Checked for power an ground at ecm plug an grounds are good but have 3v to ecm. Checked power atbthe fuse an the ignition fuse has 12v but ecm has 3v. Block has 12v coming in to it but ecm fuse an one beside it has only 3v. So was thinking fuse block was bad an changed out fuse block but still no power to ecm checked all grounds on engine an looked over wires where else could in look
No crank
- Thread starter ncdmax03
- Start date
ohm the wire from fuse block to the ecm. you have an issue there, it sounds like
Animals chewing wires (especially in a truck that sat) is not an uncommon thing (happened to mine in a CLEAN garage. Also, when working on an engine, things get moved, hit, kicked, pinched, etc and a wire that may have been compromised before (but working), was moved or contacted while working on it, and is no longer good. If it breaks inside of it's sheath, it is almost impossible to spot by eye (a meter able to ohm out wires is your best bet at that point).
When you have 12V on one part of a circuit but only 3V in another part, my first thought is high resistance. I think James is right.
Check the voltage on each side of each fuse. They should be the same. Then pull the fuses that have 3V on them and see if they are making good contact. Clean them with contact cleaner, brake cleaner, etc. Sometimes pulling and replacing make a difference. It looks like there is corrosion in that fuse box. My wiring diagram shows 2 -15 A fuses and a 10, not a 15, 25, and 10. Look on the underside of your fusebox cover and see what the names of the problem fuses are.
Check the voltage on each side of each fuse. They should be the same. Then pull the fuses that have 3V on them and see if they are making good contact. Clean them with contact cleaner, brake cleaner, etc. Sometimes pulling and replacing make a difference. It looks like there is corrosion in that fuse box. My wiring diagram shows 2 -15 A fuses and a 10, not a 15, 25, and 10. Look on the underside of your fusebox cover and see what the names of the problem fuses are.
Can you please follow the direction of what was asked? Please use YOUR fuse box lid to determine what circuits they are. We're here to help but we're not going to wipe your rear for you.
take apart the fuse block and look in there for any chewed wires or missing insulation.
what we are asking you to do is back track the wire that has 3v. you need to find that fuse, verify 12v on each side of the fuse (you can do this by putting the DVOM pin on that little silver pin on top of the fuse, its a fuse test point), if its 12v on each little point, i would open up the fuse block and then test for 12v at the wire coming out of that fuse.
if you are not sure what wire is "to ecm", pull the fuse and see which side of it has 12v power, the no power side is the side to the ecm.
you may have a bad fuse to connector connection, eaten wire, or something else causing it but what you are doing is chasing where the voltage drops from 12v to 3v to find the issue
Fuse block is tore apart an there is no chewed wires or broken wires to ecm your check the #1 #2 fuse in diagram there is no power on them now have 12v coming in power supply to fuse block (the whole fuse block) but don't have any power at the terminals for these 2 fuse that make more sense
