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2002 Mack CL Electrical Issue


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We have a 2002 Mack CL with the ETEC 460 that is giving us an occasional blink code 6-4.  When the electrical malfunction light comes on, the truck stays running but has no throttle and rpms go to 900.  We discovered by accident that if you tap on the kick panel on the passenger side, the code will always clear and the truck will run fine again, but you can never get the code to set by tapping the kick panel.  We checked the wiring plugs on the ECU and VCU and everything looks good.  It seems to be extremely random and some days the truck is completely fine and some days the code comes and goes. 

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Hey bud, 6-4 is a communication code for the 1939 line... it's the yellow and green 'twisted pair'..  check the pin condition and tension at the VECU, and at the Diagnostic port, under the dash above the clutch pedal..  check voltage at these 2 pins,, low side is about 2.5 volts and high line is about 5+ volts... I dont remember the exact volts but im pretty close.. there is also a triangular duetch plug on the firewall along with the many harness's near where the steering shaft comes out of the wall..  I know you said you can kick the panel and it changes the truck.. so maybe you missed something during inspection..   jojo

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  • 1 month later...

Thanks @Joey Mack.  Checked the plugs you mentioned, took them apart and looked at them.  Everything looked good, pins were all clean.  Put it back together and it hasn't acted up since.  Hard to troubleshoot when it happens so random and never acts up long.  Weirdest thing the last time it did it was you couldn't shut the truck off, if you turned the key off if would shut down but just before it stopped completely, it would fire back up and stay running.  Did that a couple times that  we cycled the key, then the code cleared and everything worked fine again.

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so to be clear is it fixed now?  if so, my guess would be that you improved a connection when you plugged things back in...   jojo :) 

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It was very random before, some days it would act up and the next day you could run it all day and it would never do it.  It always would go away as soon as you started to try to diagnose it.  Hasn't done it since we checked all the wiring, although we haven't used it much since, so we will see.  Hoping that fixed it. We don't use the truck every day and sometimes it goes a couple of weeks without being used.  Thanks for the help

 

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  • 1 month later...

Well the truck sat unused for a couple of weeks.  Used the truck again the other day and the issue is back.  Put probably 3-4 hours on the truck and it did it once while pulling a pretty good hill.  Smacked the kick panel on the passengers side and it cleared up and ran fine the rest of the day.  This thing is making me pull my hair out.

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Man I wish I had been in one recently..  to refresh my memory.  I know there is a group of ground wires left of the fuse panel behind the panel that says CL 700..  Have you checked it?  

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I dealt with a similar issue with the transmission controller on a Cat D5 dozer.  It would lock up and the machine wouldn't move, smack the TCM with a wrench and all is fine.  Never had to deal with it any further but would've replaced the trans module if had to.  I wouldn't rule out the possibility that the VCU behind that kick panel is going bad.

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Hans, there is only one in the kick panel...  the other is ABS..   your right..  

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