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Help! Cat 3126 won’t crank

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RVF Newbee
Feb 12, 2023
We have a 2003 mandalay 40b with a CAT 3126 engine and a freightliner chassis.

Backstory: We had engine serviced on 08/10/2022. We left FL 08/19/2022 to head to Nashville for work. We noticed the voltage decreasing when we were in Georgia and a few minutes after, the dash completely went out while driving, but the engine was still running.
Pulled over, engine was still running. After about 15 mins, manually killed the engine.
We had a mobile mechanic come out to change the alternator while we went and got new batteries. After all that was in we tried to crank it and it would barely crank before engine cut off.

We got it towed to a campground near Augusta and have finally gotten a CAT mechanic to come out and try solving the problem. We told him we thought it was electrical because of the dash going first, but he started looking into the fuel system and changed out the regulator. Still no luck cranking up.
As a “last shot” he used a small tool (picture added) to pierce a wire that he used to jump the ECM in pin 70. When he did this, she cranked right up and ran beautifully for close to a minute. As soon as he disconnected that wire from pin 70, engine died. He then told us it was an electrical issue (obviously). CAT wants almost $5k for a $300 part replacement, 3 visits, and 14 hours of “labor” (head scratching). After messing with the ECM our dash now stays on (as shown in picture) when the key is in off position and even removed. We turned our batteries off to protect them of course but this issue did not exist before he toggled with the ECM.

If anybody has any idea how to get power sent to the ECM in pin 70 when key is in the crank position, please help!! We are almost certain that will get out girl back on the road!


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