mcratchet1 Posted August 15, 2019 Share Posted August 15, 2019 ok i have a 2006 mack mr688s (032711) with a concrete boom sitting on it. The truck would act like it was shut off but never cut out, the code is coming from vecu. It was happening once a month then once a week now 2X daily i checked from the batteries to power relays and everything in between and cannot find anything, the starter, alternator, engine grounds, frame grounds, the ground relay on drivers side by air filter behind little black cover its very annoying especially while pumping concrete any other trouble shooting advice would me great thanks!!! Quote Link to comment Share on other sites More sharing options...
fjh Posted August 15, 2019 Share Posted August 15, 2019 (edited) If it has a night switch bypass it temporarily. Edited August 15, 2019 by fjh Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted August 16, 2019 Author Share Posted August 16, 2019 u talking about battery disconnect switch? Quote Link to comment Share on other sites More sharing options...
fjh Posted August 16, 2019 Share Posted August 16, 2019 yup Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted August 21, 2019 Author Share Posted August 21, 2019 ok no luck on bypass same problem Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted September 5, 2019 Share Posted September 5, 2019 Replace the key switch. You checked everything else. Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted September 5, 2019 Author Share Posted September 5, 2019 actually i just replaced the key switch monday, problem seemed to go away until yesterday it dropped out while he was pumping Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted September 5, 2019 Share Posted September 5, 2019 (edited) Did you go completely through the 9-2 service bulletin point by point? Are you Fleet, Private or Dealership? Edited September 5, 2019 by Mack Technician Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted September 5, 2019 Author Share Posted September 5, 2019 yes, the only thing i do not have a pin tester to check relays, but the did have good scratches and fit tight we are a small private pump company we have 7 mack trucks I called mack for a diagram of the fuse and relay layout in the dog box but they said they cannot give me that info they are never helpful 032711 is the last 6 of vin do you have access to fuse and relay location? Thanks Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted September 5, 2019 Share Posted September 5, 2019 Sorry, don't have access...… Get 2 pizzas and a flat of printer paper and show up at the dealership during the nightshift. They can print out the whole thing for you off impact. Make your own diagram book. If I owned the truck I'd be tempted to ease a few wires and grounds out of critical low amp control circuits and take control. Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted September 5, 2019 Author Share Posted September 5, 2019 tell me which ones to take off and i would gladly do so to test it out Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted September 5, 2019 Author Share Posted September 5, 2019 thats a good idea but they dont work nights here Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted October 4, 2019 Author Share Posted October 4, 2019 ok found high/low beam relay bad changed been running with no problems for a month now did same thing 2x today also this morning truck would not start. When i turned key only heard buzzing coming from these 4 relays. Does anybody know what these control? im guessing one has to be starter i cycle the key a few times then it cranks i checked to the wire had 11.50 but when i turned key switch dropped to 5.5 volts now truck will not start going to just start tracing wires unless someone could help a brother out Thanks!!! Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted October 5, 2019 Share Posted October 5, 2019 (edited) If they’re buzzing you have a short to ground on the power output of the relay(post 30’s output side). If you have a 30 AMP relay they buzz if you try to draw more than 30 AMP through them. Protection feature. Those are more than 30 amp. Hard to read. Edited October 5, 2019 by Mack Technician Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted October 7, 2019 Author Share Posted October 7, 2019 ok ill check there 70 amp relays Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted October 7, 2019 Author Share Posted October 7, 2019 whats a typical cause ? rubbed wire? Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted October 7, 2019 Author Share Posted October 7, 2019 on all 4 power rely's #30 has power and #87 is ground Quote Link to comment Share on other sites More sharing options...
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