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Vmac III 9-2 lightning flash code


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You need to clean ALL the grounds, starting at the batteries.  I bet the ground bolt on the block in front of the starter is loose.. the svc. Bulletin for 9-2 has the steps. Or you can look it up in my posts and find the book I wrote on it..  :). 

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My mr688 would crank but not start. I'm guessing yours is the same because you are getting enough power to the key to give you the 9-2 code.  If yours won't crank then you may have a power fault somewhere else, maybe the ignition itself.

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The truck eventually stopped the one crank it gave before it stopped and showed no power. The power never came back. I’ve turned it in to the shop and they have said my ECM has no power. They put a test module/ one of their own and my truck started right up. They told me let’s go ahead and rebuild the ECM and I agreed.mind you I bought this ECM July 2021 I’m appalled that what I feel like is still a new ECM(to me) has gone bad and needs to be rebuilt…

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Bad batteries?... EECU won't turn on with low voltage, I forget what the minimum voltage requirement is. If your batteries are toast or alternator died then I could see you lose EECU power and also lose crank... But I've only got experience with the one computer truck. Our other trucks are mechanical.

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10.5v ish... I have used a seperate battery grounded to the truck and a lead from the positive to fuse #40 in the EPDM and got a Mack to start and run..  This was to diagnose a similar ''will crank, but wont startup'' complaint...   It turned out that the starter was pulling too much power and it was starving the EECU..   Jojo

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Yesterday I checked each of my batteries (3 only) worth a battery tester and they all showed about 13ish volts separately so the batteries were good. I myself and a couple of my owner operating buddies checked the fuses in that little box on the driver side hood, also in front of the passenger seat that compartment and by the passenger sides feet. It did seem like no power was happening from or around the ECM. Then I got todays news, which was what I shared with you guys today a few hours ago. The ECM is currently being rebuilt I should have my semi back by tomorrow. Just hoping THAT really was the issue and not the alternator or starter or something. You know when you go to the doctor and show symptoms and you figure out the solution? Problem solved hopefully 🥲🥲

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Hope ecm solves it. Any time I check batteries I check resting voltage, then have a helper try cranking it while I'm watching the test voltmeter. My car battery started being unreliable the past couple months. Voltage always tested good, but it was losing cranking amps for some reason. Left me stranded a couple times before I ponied up for a new one.

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15 hours ago, JoeH said:

Hope ecm solves it. Any time I check batteries I check resting voltage, then have a helper try cranking it while I'm watching the test voltmeter. My car battery started being unreliable the past couple months. Voltage always tested good, but it was losing cranking amps for some reason. Left me stranded a couple times before I ponied up for a new one.

That "load test" will frequently show you a bad battery that the static test won't.  Great tip, Joe!

"Eagles may soar, but weasels don't get sucked into jet engines."

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I will definetly be changing out my batteries before the winter comes. The ECM has been rebuilt and my truck has started right up. I’m still flabbergasted about this ECM only being 2 years old and already needing a rebuild. Could a short cause this to damaging the ECMs power??

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