Hi guys I'm back again lol, just pulled in a M1078A1, with the ABS light on, as soon as I started it up I noticed the CTIS controller was unplugged which obviously caught my attention, decided to plug it in to see how the truck would react and low and behold, additional lights started coming on with the charging voltage dropping to zero, I was watching the lights on the CTIS controller to see how they'd react and they mostly flickered like it was a bad connection or ground but eventually all 5 just stayed lit constantly. Interesting, so I pulled it into my bay and hooked up or Snap-On PRO-LINK to see if it was throwing any codes, none, tested out the ABS light, that works. So my guess is the CTIS is causing the ABS light to stay on, I'm gonna check the harness going into the controller/power and grounds but I don't have the schematic sheet associated with the harness, does anyone know what pins have power and ground on the harness side?
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M1078A1 ABS Light on
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Ronmar
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did the reader function OK with CTIS connected? one potential issue we have seen here is the bad module pulls down/corrupts the data bus causing the other faults, and in some cases frying the bus end loading/termination resistors...
5 solids is usually a dead CTIS controller(failed internal BIT check?)
5 solids is usually a dead CTIS controller(failed internal BIT check?)
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For the ABS light check the sensors at each wheel. Sometimes they get pulled out to far and don’t sense the tone ring. Usually just tap them in further. But it has to be driven to clear the code ensuring it senses each wheel rotating.
I unplugged the controller before I hooked the PRO-LINK back up, as I suspected it would cause false codes to popup, I was mostly seeing if anything was stored and there was nothing. From what I've been researching I'm seeing the same thing Ronmar, the controller looks like it's toast which could definitely explain the additional lights coming on along with the charging system dropping.
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The ABS light comes on, then off quickly at power up. Then if the controller is working you can hear the ABS system check front, back, front, back. Then if the system fails the light comes back on steady.
If the CTIS controller is one from a unit other than the M1078A1, the pinout may be different, especially if from a unit that does not have diagnostic comms. As @Ronmar mentioned some CTIS units are pinned out in a way that burns up the M1078A1's J1939 comms, specifically the R12 and R13 resistors.
Here is a comparison between the M99A2 CTIS system and the M1078A1, with schematics below.
View attachment 913437
M1078A1 <18500 schematic
View attachment 913438
Hopefully it helps—
If the CTIS controller is one from a unit other than the M1078A1, the pinout may be different, especially if from a unit that does not have diagnostic comms. As @Ronmar mentioned some CTIS units are pinned out in a way that burns up the M1078A1's J1939 comms, specifically the R12 and R13 resistors.
Here is a comparison between the M99A2 CTIS system and the M1078A1, with schematics below.
M939A2 schematic
View attachment 913437
M1078A1 <18500 schematic
View attachment 913438
Hopefully it helps—
Ronmar
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Charge voltage dropping is a weird symptom, unless it is confusing the crap out of the MMDC... With 5 solids it is probably the CTIS box, or a power feed issue , in which case a new CTIS will have the same issues
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Does an M1078A1 have an MMDC? or would that be an M1078A1R or newer?
The
Additional lights and voltage drop is a weird symptoms. What lights, where did the voltage drop?
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Cab grounds......
I believe it was check engine, check trans, some other random lights but they went away as soon as I unplugged the controller, remind me what the MMDC is? I'm not familiar with that one. Charging voltage on the 24V side would drop to zero according to the guage.
Yes, remind me again where they are located? Or are you referring to the ones that sit behind the PDP?
Ronmar
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What year is this truck? The MMDC is the digital controller that drives the bussed/digital/electronic gauges. located under the drivers dash. All those check lights along with ABS could be caused by corrupted data buss information...
Grounds:
Starter to drivers frame
alt to pax frame
cab to pax frame behind grill
inside cab to pax dash under/outboard power panel
same point to power panel ground point which feeds TB2(ground terminal buss).
disassemble, strip off carc to bare metal, throw the star washer in the trash, re-assemble with copper coat or dielectric grease between terminal and bare metal, lock washer and torque appropriately. re-coat over the entire thing with whatever paint is approved for carc touch-up to protect it from the weather...
Grounds:
Starter to drivers frame
alt to pax frame
cab to pax frame behind grill
inside cab to pax dash under/outboard power panel
same point to power panel ground point which feeds TB2(ground terminal buss).
disassemble, strip off carc to bare metal, throw the star washer in the trash, re-assemble with copper coat or dielectric grease between terminal and bare metal, lock washer and torque appropriately. re-coat over the entire thing with whatever paint is approved for carc touch-up to protect it from the weather...
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The one behind the grill is the most important for the gauges and computers in the cab and powered by the cab ignition relays to not freak out.
Put your meter on a DC Volt setting that will read ~5v and with everything turned on (engine, lights, etc) check for voltage potential between the passenger dash grab handle bolt and the alternator ground point on the frame in the passenger wheel well. If it reads anything higher than 0v you have grounding problems.
Put your meter on a DC Volt setting that will read ~5v and with everything turned on (engine, lights, etc) check for voltage potential between the passenger dash grab handle bolt and the alternator ground point on the frame in the passenger wheel well. If it reads anything higher than 0v you have grounding problems.
Ronmar
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yep, developed voltage between the different ground points = resistance, probably in the connection points. All wires have resistance so you will see voltage, when doing this voltage drop test. it should just never be more than ~3% of the voltage carried by the circuit, or ~.84V for a 28V circuit worst case with the circuit carrying full rated load...
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Which they realistically never do (carry full load). I'm going on a cleaning expedition if I see more than 1/4 volt.
Ronmar
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Exactly! The max cab load is probably under 25A for 14/28 combined, and the cables they used up to the power panel are probably good for close to 100A at those lengths, so you should see very little voltage drop on any circuit under normal use...
Thats a great tip, thank you very much General
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A 2007 M1078, is an M1078A1R isn't it? This truck should have a C7, MMDC, a different PDP, than an M1078A1 I believe—
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Correct. Technically according to the manuals it's an A1 with serial over 100,000. Which in practice occured in the middle of 2004.
We call them A1R. S&S called them that too. The military didn't adopt that nomenclature. There's a couple dozen serial number ranges in the A1 series that creates serial number splits in the manuals but it's still an A1. A1P2 is a thing, A2 is now a thing also. A1R is a thing that died with S&S. But it is useful to describe trucks with this advanced feature set as they are quite different.
We call them A1R. S&S called them that too. The military didn't adopt that nomenclature. There's a couple dozen serial number ranges in the A1 series that creates serial number splits in the manuals but it's still an A1. A1P2 is a thing, A2 is now a thing also. A1R is a thing that died with S&S. But it is useful to describe trucks with this advanced feature set as they are quite different.