2011 Mack CXU600. no crank no start.

2011 Mack CXU600
1M1AW02YXBM015137
Eaton 8 speed

Customer states truck would intermittently not start, said driver could wiggle ECM connector and got it to start once. Pulled into shop and check all the fuses, all were ok. confirmed is would not start. wiggled on harness for a while and was unable to get truck to turn over. un plugged and checked connectors and all were ok. sometimes it would just start to engage the starter then stop. checked and confirmed I am getting power to starter, confirmed soft start works. can ground out soft start and truck will TURN right over but no start. wiring diagram shows a starter relay control driver circuit to ground out starter relay directly form ECM. it is not sending signal to ground. checked circuit for shorts to power, ground, resistance, load tested and even ran a temporary new circuit to no avail. I do now know the logic behind this starting system, un plugged and checked the oil temp sensor as I read this could cause it as well. anyone else run into this issue? customer is insisting it is the engine wiring harness but I'm hard pressed to just replace parts. checked for codes and have codes. INFORMATION DISPLAY PPID 278 Aftertreatment Reagent level FMI 9 abnormal update rate, active, 1 count. INFORMATION DISPLAY PSID 200 data link MID 128, FMI 9 abnormal update rate, active, 1 count. VECU PSID 200 data link MID 128, FMI 9 abnormal update rate, active, 5 counts.

 

anyone?

 

Does it happen to have a battery off switch? They do go bad and occasionally do some weird stuff. Mine would crank but would not fire and the gauge cluster would die. The TCS would only be illuminated.

Good luck

 

no battery cut off, replaced ECM. still nothing. throwing the white flag up and sending it to the dealer. hope they can figure it out. I called and asked them about it and they were scratching their heads!!! they have more resources than I do. just want to get this truck back on the road for the customer. thanks

 

7.2L diesel engine needs about 510 amps to turn over. (normal temp start)therefore if it cranks slowly its probably not getting enough amps too turn over. ( load test batteries etc.) If it wont crank at all i would go find the magnetic switch for the starter circuit and jump the poles the head to the starter. the link between the starter and your key is the magnetic switch( could be called heavy duty starter relay)turning the key to start magnetizes that switch which closes the circuit to open up the juice to the starter. if jumping this cause the starter to crank normally, problem is the magnetic switch. your probably looking for parasitic draw somewhere in the starting circuit. max voltage drop in a starting circuit is 1v. (pos and neg)if all checks out with stating circuit, your problem is not there. hope this helps.

 

See if these will help you next time.

 

I did all those checks, problem is ECM is not sending ground signal out to relay to allow it to start. I can jump it and it will cranks over all day but not fire. something somewhere is not allowing it to get the ok to start. Batteries are fully charged.

 

that would have been PERFECT., I was using Mitchel wiring diagrams and no where did they have the EMS relay in there stating it was part of the starting circuit. thanks a lot. printing that off and putting it in the oh #### binder

 

Most common problem with ecu due too multiplexing is ground. That particular circuit is grounded through the ecu with terminating resistors at each end of the circuit. If that circuit is short to ground, the signal goes directly to the battery which it's not supposed to.

 

Means that circuit is grounded but not too ecu. Direct to chassis ground. Its a longshot, but I've seen it happen.MMy problem was the diagnostic plug. Someone added a ground directly to chassis ground and not only could I not communicate with the truck computer, but the automated transmission and a bunch of other crap wouldn't function. Took 1 week to find a wire about 3" long that didn't belong there.