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