intermittent power lost to ecm

Rookie Here....
We had a truck shut down in Grantsville, MD. Towed in to JL Truck Services & Tires or Cumberland, MD. Next morning he worked on it till afternoon, came back to and told me its ready. We had a corroded power line to ECM he replaced it with a new fuses and patch of wire, a partial not the whole line. Driver went in pick up the truck it was running fine, after he was hooked to the trailer, truck stalled again, they took him back in the shop and came back telling me that ECM is blown because of corroded wire. my question is, why would truck start at and runs fine for the first time when he just fixed it with fuses and partial power wire to ECM.
Is it that they must have done something stupid while putting that patch of wire that blew ECM. We ended up with $3700 repair, he was trying to get away with the core not pay me anything. When I talked to the freightliner where he bought ECM from, they gave me core value. But on the other hand JL Truck Service charged me $150 to pickup the ECM and $225 for 3 hours labor to go pick up the ECM. BS!
total of $375 to pickup the ECM. 300 miles down the road truck brokedown again, with same problem!
To be continued

 

I had the same problem I wound up running a new power wire from fuse box to ecm and the problem went away.
It was a 3 dollar fix that had cost over 1200.00 for the shop to not figure out .
it has been over 4 years since i did this and haven't had any trouble since.

This worked for me but as you know this might not work for you.
But I would at least try a new power source from fuse box to brain box it dang sure can't hurt !!

 

Usually when the ECM shuts down because it lost battery power it will log a code. If it losing ignition (or key) power the key on/off counter will increase. It helps to further diagnose power problems. Most ECMs have more than one power wire. You may just have to run the engine and then grab and start shaking the wire harnesses to the ECM to see if you can induce the problem and find the problem area. I have seen new wires installed but they did not replace the actual terminal in the connector body and the terminal is completely worn out. I have also seen improper butt connections that failed right away. ECMs are pretty tough, I would replace one only as a last resort!

 

A CAT Engine takes three different 12 volt power supply wires to the ECM. 1) keyed from the ignition switch to pin 70, 2) 12 volt battery power to pin 52, 3) 12volt battery power pin 53

Usually pin 52 and 53 are feed power from the battery on one wire that splits before the two pins at the ECM. You should find a fuse in the battery box for this power source. If you lose power at both these pins at the same time the ECM will never show a fault code.

You also have two seperate ground wires on pins 65 and 67. Again this wire usually leaves the battery box as a single wire splitting into two at the ECM.

I'd say the problem is on one of the wires leaving the battery box and before it splits into the seperate pin locations.

 

I had the same issue this winter on my '98 WS 3406. My driver called and said that the truck shut down. She was able to get it going but said that as soon as she turned on the lights of heater fan it would shut the truck down. It shut down on her several times but she was able to limp it back to camp. We went up the next day with the scissor neck to get the truck and when we got there, the truck fired up, we drove it onto the trailer and hauled it to grande Prairie to the WS dealer. It fired right up to unload it from the trailer ran perfect. The mechanic said he found 1 code loss of voltage to ecm but couldn't find anything wrong and couldn't explain one code when the truck had shut down several times. I drove the truck home (120 miles) and it never missed a beat. Thought perhaps a bad groiund but not sure where to start looking.

 

The pin locations I gave for power are for the 70 pin ECM. The 40 pin ECM only has three pins for the 12 volt power source. 1)keyed + battery is pin number 6, 2)unswitched + battery is pin number 4, 3)- battery is pin number 5 and should go to the grounding stud on the cylinder head. Here's a copy of the wiring diagram with pin location on the plug to be able to read with a multi-meter

 

When you look at the plug on the 40 pin it's the top three pins on the right hand side for power and ground

 

hey Mr.Haney.are the above pin positions the same for a 70 pin e.c.m. on a 2000 3126?

 

yes, they are the same. Even the newer engines the cab to ECM plug is a 70 pin plug and the pin locations are the same as the older trucks

 

As the op of this thread, I thought I would give an update on this issue in my case. I would like to also give a thank you to all of those who took the time to offer solutions. The solution that was spot on was getting clean power from batteries directly to the ecm.

What was done to solve the problem the first time (i thought) was replacing all batteries, all battery cables connecting batteries (except the battery cables running from batteries to starter), cleaning all connections, cleaning fuse holders, check for lose connections at plug that connected the wiring from batteries to ecm, then checking for lose pins at ecm.

Well I thought this issue resolved until Monday night after getting loaded. While updating my log to start heading out, truck was idling, engine sputtered which thru the stop engine light and check engine light. The stop engine light went out, but check engine stayed on. (Engine stayed running). About a mile or so down the road, same thing happened, I was in the middle of the road and truck was still running, so I started to find a place to pull over. I got maybe a block and truck just turned off (like I turned off the ignition key). All the lights worked, I could crank the engine, but would not start. With key turned on no lights on the vigil bar on dash were lighting up. This was my clue there was a loss of power to the ecm. This time around was worse than the first time, which the truck eventually started and I got it home. This time around truck needed to be towed.

The solution this time around was to make all new wiring straight from the batteries to the ecm. The original wiring from batteries to ecm was completely removed. Crazy thing, when the mechanic started to work on the truck, he decided to try starting it. D**n it if that darn truck fired right up! Every time he tried to started it, it would run. He wiggled all wires to try and get truck to cut out and nothing, it stayed running. The mechanic found moister in the plugs at the ecm and corrosion in the original fuse holders. His theory is moister was getting into the wiring and causing enough resistance and voltage drop to turn off the ecm (As you all know it takes 10.5 volts to fire the N14). The mechanic cant seem to figure out how moister got into the plugs at the ecm.

On both occasions of losing power to the ecm, it had recently rained. Not sure how that correlates.

It has only been a week, but so far so good ... at least for that problem.