Possible MCI D4500 Computer Problem?

Glennman · October 03, 2020, 05:36:40 PM

Hey guys... I've been gutting my bus overhead bays, ducting along walls, etc. No welding (I'm familiar with cutting all power first if I had been). I've cut off a lot of wiring along the way, but only the wiring in the upper luggage bays that lead to the lights, speakers, etc.

I fired up the bus today, since I haven't ran it for a couple of weeks.

It started ok, but there is a light on the dash that says "Network Failure" (and wheelchair door open. I'm still trying to figure out how to bypass the safety stuff there). The bus starts ok, but now the fast idle won't work, the fuel pedal doesn't do anything. I don't have any kind of manual or wiring diagram. I've been in contact with MCI to order a manual, but to no avail. Is it possible that I fried the network somehow? Again, the main shut off has been off, and I have done no welding.

I suppose I should have researched the wiring better before removing the upper bays, but I have the power supply disconnected that feeds everything in the bays, and it is all pretty easy to see that it doesn't go to anything with the engine controls. Thanks all! Glennman

richard5933 · October 03, 2020, 05:50:00 PM

I have no firsthand experience, but I do remember reading about others who have had issues with weird things happening when they removed the overhead bins and the associated wiring.

Maybe do a thread search to find out what the solution was in those situations.

luvrbus · October 03, 2020, 06:09:33 PM

Yep you have cut a wire going to something that is a interlock,will the shift pad shift ?

belfert · October 03, 2020, 06:11:28 PM

You might have wires running through the overhead bays that are important. I chopped off the wires in my overhead bays as I thought they all went to the non-working HVAC control panel in the back, but I found out I also cut the wire for the marker lights in the rear. That was an easy fix.

Glennman · October 03, 2020, 11:19:31 PM

Quote from: luvrbus on October 03, 2020, 06:09:33 PM
Yep you have cut a wire going to something that is a interlock,will the shift pad shift ?

Nope, that too. The shift pad will not shift, the fuel pedal does nothing. Could it be a safety thing that prevents the operation of the bus because it thinks the wheelchair door is open?

Busted Knuckle · October 04, 2020, 04:51:07 AM

Welcome to the madness! Those buses were a known headache to mechanics from day one with all their crazy CAN systems and multiplex computer systems.

But yes somewhere you have cut a wire that is indicating something is wrong.
It may or may not be the wheel chair door sensor, or something totally different that just shares that warning circuit.

I'd start AT the sensor for the wheel chair door and trace the wires back toward where ever they go from there. If you find one cut splice it, if not your in for a long fun ride to find what you did cut.
Another idea to reconnect wires you cut one by one until you get the one that fixes the problem.

BK

luvrbus · October 04, 2020, 05:37:26 AM

The wheel chair interlock is programed through the transmission so you cut the wires they come up from the rear on the passengers side through the overhead baggage .You may need to go the MCI page on F/B to get the wiring schematics for the ramp I gave Yvan all of mine,MCI download manuals are not that great

chessie4905 · October 04, 2020, 07:08:07 AM

Go to Harbor Freight and buy a Cen Tech cable tracker; less than 25 bucks. Will be invaluable to sort it out. really easy to use and pinpoint cut circuits.

Glennman · October 04, 2020, 08:08:17 AM

One thing I didn't do was hack and slash all the wires. I did cut some, obviously, but for the most part, I unplugged most of them and the ones that come out of hidden places (ceiling/floor) are still hanging there with the plugs on the ends. I did cut some after those plugs that are within the bays. I still have all the wires too. I suppose some backtracking is in order. I've been watching Yvan's videos lately. Maybe I can comment on one of them to get his attention, or look for him on Facebook. Thanks everyone!

luvrbus · October 04, 2020, 09:25:03 AM

There are a couple of MCI employees on Yvan's F/B page that will answer you also they are sharp on MCI's D model

Glennman · October 04, 2020, 04:16:38 PM

Quote from: luvrbus on October 04, 2020, 09:25:03 AM
There are a couple of MCI employees on Yvan's F/B page that will answer you also they are sharp on MCI's D model

Sounds great luvrbus! I'll see if I can find their page. Shouldn't be too hard. I just today finished (for the most part) taking down the rest of the upper bays. I'm paying a little closer attention to the wiring (a little late I suppose!).

someguy · October 04, 2020, 06:18:58 PM

The schematics for your coach are available online at mcicoach.com

What unit number is your coach ?

I'm guessing that there was a multiplex module in one of the luggage racks and you cut the bus wires to it and took down the main bus. The module might have been used to control lighting or the A/V system.

If you cut the multiplex bus wires, they need to be terminated, usually with a 120 ohm resistor. Or you may need to reconnect the computer so it can communicate with the rest of the bus.

It should be fairly easy to figure out. The wiring schematic from mcicoach.com should give you the colors of the multiplex bus wires. You can then go check the wires you've cut to see if any of them were the bus wires.

someguy · October 04, 2020, 06:26:40 PM

This should be the schematic for your coach.

Correction: I don't think your coach has the Multiplex system.

someguy · October 04, 2020, 06:56:06 PM

I looked at the schematics for a 2000-2003 MCI D4500.

The only network I see is the J1939 that goes between the ECM, transmission controller and driver's station.

Bus wires are usually twisted pairs. Did you cut any twisted paired wires ?

What transmission does your bus have ? Autoshift ?

Glennman · October 04, 2020, 11:24:42 PM

Quote from: someguy on October 04, 2020, 06:56:06 PM
I looked at the schematics for a 2000-2003 MCI D4500.

The only network I see is the J1939 that goes between the ECM, transmission controller and driver's station.

Bus wires are usually twisted pairs. Did you cut any twisted paired wires ?

What transmission does your bus have ? Autoshift ?

Thank you someguy... I'll check out those links to the schematics. My bus has the Allison 6 speed, but I don't know what model (B500?). I haven't had it very long, so I'm still learning about it. It has the square impression pad with D N R and some arrows. You have to push the brake all the way down to go from N to D. Of course now, it won't do that. I don't recall cutting "pairs" of wires. I still have most of the harnesses with the large round 20 (or so) pins inside.

What do you mean by terminating all the way? That sure sounds good! Also, I don't believe my bus has the "Gold Bricks". Is that what you refer to as a Multiplex system?

Too many questions I suppose. I'll be looking at the harnesses I have and see what they look like. Thanks for all your help!