MCI-DL345 high speed idle, shift pad dead

plyonsMC9 · January 25, 2021, 11:23:12 PM

Good evening bus folk!

I'm trying to locate the vehicle interface module, as I need to check the fuse contained in that unit - troubleshooting the Allison shifter pad - stopped turning on. The bus is a 1994/1995/ DL3-45. Could someone please advise? Maybe a picture? I've got conflicting advise as to where it's located. Searching but w/o success. Other fuses checked and working (driver side junction box, j-box in 1st bay behind driver, battery bay). Trans is HT754.

Thank you!! ,Kind regards, Phil

luvrbus · January 26, 2021, 05:07:56 AM

Bummer that is 1st generation ATEC Allision and I don't have a shift pad to bring you I don't have a schematic for a DL3 with that transmission,fuses are located in the 2 places you mention on DL's with B500,you need to remove the pad and look for a ground and test the pad with another source of power if it lights up the pad is good or check it with a VOM meter if you have one, but I am thinking the pad is bad and those are hard to find good luck if you don't it get going I will try to come to you tomorrow if I can find a loner pad give me call later

plyonsMC9 · January 26, 2021, 10:39:32 AM

Thanks very much Clifford,
Talked w/ Boris @ MCI tech, he clarified, this is actually an Allison HT748

I now have some detailed schematics from MCI on the transmission for troubleshooting.

Best Regards, Phil

plyonsMC9 · January 26, 2021, 12:18:26 PM

Again thank you Clifford.

I'm going to take off work early & do some more troubleshooting at 3PM so maybe I can make some headway. I will give you a status update call later today after the (hopefully) productive troubleshooting work.

Also, I'm retracting my request for a VIM location, since with the 748, that doesn't exist.

Best Regards, Phil

DoubleEagle · January 26, 2021, 02:35:28 PM

I would check the Allison ID plate on the actual transmission (driver side) to verify what model it is. Allison experts told me I had a HT741, but when I crawled underneath the plate clearly said HT746 on my 1994 Eagle.

plyonsMC9 · January 26, 2021, 02:46:37 PM

haha! Point well taken, I will do so!
Thanks Walter,

luvrbus · January 26, 2021, 06:30:10 PM

There is no difference in 741 to the 748 the last number tells you how many upgrades was made to the 741 and most were minor 99% were electronic upgrades ,the 755 is a five speed,still don't why that bus has a 748 only one I ever saw in a DL3 most were B500 with 60 series.Phil I have the Allison manual for the 748 if you need it let me know

plyonsMC9 · January 26, 2021, 08:01:37 PM

Greetings bus folk,

Update on today's troubleshooting;
Found out the transmission type, and thank you Cliff for the numbering system information. I say it's an HT748, though I haven't yet directly read the plate to verify. Cliff, I don't have the manual for the 748, just a troubleshooting page from MCI. Gary may be able to get the electronic version to me. I really appreciate that offer. Thank you Cliff.

Quick history: Zero problems with the bus until engine batteries went dead, and had to re-charge the batteries from zero. From that point forward the electronics seemed "off". During the charge process I did disconnect each battery and the 24v disconnect, charging each battery separately until the bus would start. After the charging and initial drive, a couple of the dash guages were dead and fuses needed to be replaced, and a buzzer was intermittently activating every couple seconds - for lavatory, of which there isn't a lavatory.

After the next few days of idle, the engine would not start. Jumping at the starter solenoid did indeed get the engine to quickly turn over, & run, however, the high speed idle would not activate and the allison shift pad would not activate - no lights. Replaced 2 of the 3 front ATEC fuses in the front bay, and the bus fired up, stopped & started several times, drove briefly, all good. Hooked up tow car, packed, started the bus, all good, went to drive, and noticed the keypad was dead again.

Today, went over a number of the circuits, especially atec circuits, took apart connections, cleaned, put back together, no good. Thanks to Fred who's here working on his Prevost for helping.

One bit of oddness is that we're getting only 1.4 volts at one of the ATEC 8amp fuses, both legs, in the first bay junction box which I thought, was 14.4 when it was running (and with the ignition in the On position). I'll probably need to post a picture of that. It's dark now. There are 3 atec fuses in a row on the outside of the forward bay junction box.

Every fuse has been tested that we've found so far, many of them cleaned. Going to ask MCI tomorrow what those voltages should read in the first bay, atec fuses.

Ideas, suggestions welcome!, Kind Regards, Phil

richard5933 · January 27, 2021, 03:52:54 AM

Have you tested the batteries to confirm that you don't have a dead cell in one? If one of your batteries is bad, you'll be chasing your tail for quite a while looking for problems. Eliminate the easy stuff first.

luvrbus · January 27, 2021, 05:37:36 AM

Phil call Kevin at 602-810-1845 and see if he has the 748 software to pull the codes for you it is not defaulting to natural I don't have the 700 series cartridge anymore or I would come do it ? did you clean the connections at ECU for the transmission and the plug that goes into the transmission (on the passengers side) a round plug on the side of the transmission

plyons · January 27, 2021, 07:54:25 AM

Thanks Richard!, yes, batteries are brand new, replaced a week ago, all voltage tests look very strong - though I don't have a hydrometer to test each cell. Agree re: easy stuff.

Kind Regards, Phil

plyons · January 27, 2021, 08:52:57 AM

Quote from: luvrbus on January 27, 2021, 05:37:36 AM
Phil call Kevin at 602-810-1845 and see if he has the 748 software to pull the codes for you it is not defaulting to natural I don't have the 700 series cartridge anymore or I would come do it ? did you clean the connections at ECU for the transmission and the plug that goes into the transmission (on the passengers side) a round plug on the side of the transmission

Thank you Cliff!, I think I've spoken w/ Kevin (Phoenix?) before. I will give him a call re: the 748 software. And no, haven't cleaned the connections at the ECU for the trans, and plug that goes into the trans. Those will be next when I can get a break from work.

Also, attached a picture of some of the voltages, test results.

Best Regards, Phil

niles500 · January 27, 2021, 01:58:37 PM

Hi Phil not familiar with your bus, but if it is a 24 volt system with a Vanner 12 volt converter you may have tripped the circuit breaker- just a possibility

plyonsMC9 · January 27, 2021, 02:47:09 PM

Thank you Niles,

You are correct sir. 24v w/Vanner

Not sure where that particular circuit breaker is but I can sure check. If you know where it is on your bus maybe that would help? Either way, I'll look.

Latest, tried a 30 minute 'reset', completely disconnected batteries. Reconnect. No joy.

MCI tech Sez I should have all three fuses (above picture) @ 13.4volts w/ignition on. One of those is at 1.3 v. All I have to do is find the issue. Diagrams are a bit confusing. But I've got a good set now from BCM Magazine.. nice resource.

Will call Kevin for the diag cartridge for the 748 after work. (left voicemail)

Kind regards, Phil

robertglines1 · January 27, 2021, 04:54:12 PM

look up wiring ddec IV it will show you trans interface and vehicle interface off of ecm. (Out there )but is your to your pad interfaced with ign switch? check out power 12 V at ign switch..Note ecm IV requires seperate fused positive direct from battery also independent ground seperate from frame. DDEC IV will shut down at 11.6V power supply. do post results so the rest of us can learn. my vanner has a red push button breaker on it.