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
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
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
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. 8)
Best Regards, Phil
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.
haha! Point well taken, I will do so!
Thanks Walter,
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
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
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.
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
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
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
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
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
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.
Thanks very much Bob,
Will indeed check that wiring - i have the DDEC II. Also see a fuse below the shift pad.
And well, I found the big red breaker button on the Vanner this evening. How could I miss it? In the IN position, not tripped. But I figure let's pop it out. Well, not a good idea when wife is cooking things - and the lights go dark & pitch black inside.
And again thanks to Fred for noticing this thread:
https://www.busconversionmagazine.com/forum/index.php?topic=31850.15 (https://www.busconversionmagazine.com/forum/index.php?topic=31850.15)
Talked w/ Kevin briefly - he did not have the software but we may talk again tomorrow.
No time to clean the plug that goes into the transmission today - will take a day off troubleshooting tomorrow as my real-job needs me to catch up.
Kind Regards, Phil
That transmission doesn't have a neutral switch but does have a neutral relay someplace in the start circuit ,I am still trying to find a shift pad I think that is your problem,the check transmission light should come on if it is throwing a code,the 700 series electronic transmission are like eating a elephant sorry to say
Phil if the need arrises here is a link to a place up North that my buddy used that rebuilt his ecu .and key pad.
https://jultech.com/
Good luck.
FWIW they make a harness to go from ddec II to ddec III..
Not much time for troubleshooting today;
But did snap a picture of the Allison Serial number plate / driver side to verify identification. Plate was covered in grease. If you need to find it, right above the oil pan - it's not real large.
Also setup a visit w/an Allison Trans specialist from Williams DD tomorrow morning. It's been almost a week of troubleshooting and we're still here. Will post updates as I receive them. Suspicion being the shift pad and the TCM, though testing tomorrow should be helpful.
Van, thank you - that may indeed be helpful. Parts are 'not plentiful' for this task to be sure.
Bob, I had no idea, and I will ask about that.
Kind regards, Phil
Phil I don't believe that's the vanner I was referencing, the one 1 (or more) I am talking about should be located near your 24v master switch about the size of a small USPS priority box - HTH
thanks Niles!, I have located it.
More updates, while the Allison tech was here troubleshooting, he pulled out, pushed back in the ATEC fuse in the front junction box near driver, then we heard a click in the front j-box and the 1st bay j-box. Then we had 26volts on that circuit.
This is an exact repeat of what happened last time when the mechanics replaced the fuse in the 1st bay/ATEC - suddenly the system came to life. So they replaced the fuse holders, fuses and thought all was happy until the ATEC stuff went dead.
So, right now, it's again, not failing - so more difficult to troubleshoot. Going over schematics, more testing.
Quote from: plyonsMC9 on January 26, 2021, 08:01:37 PM
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.
Ideas, suggestions welcome!, Kind Regards, Phil
Your very welcome, nothing worse than an intermittent problem that fixes it self when you stare at it hard enough!!!
Quote from: plyonsMC9 on January 28, 2021, 09:19:01 PM
Not much time for troubleshooting today;
But did snap a picture of the Allison Serial number plate / driver side to verify identification. Plate was covered in grease. If you need to find it, right above the oil pan - it's not real large.
Well surprise, surprise, it's a HT741! See what happens when someone assumes what it is. From the outside appearance the 741 and 748 look very much alike, but if you had a HT746, it would look a lot different even if the internals are very close.
Walter the transmissions are the same the models changes you posted a picture of a 746 with the retarder with a few parts missing they bolt to the rear of a 741 to 748 they will have 2 numbers in front of the 7XX and 2 or 3 numbers after the 7XX to identified the application,the Allison parts manual cover all 700 series electronic transmission and you will not find a foldout on the 741 or 746 it has only the updated 748,they are the same transmission as the 740 with 8 electronic updates and valve body
Not counting the retarder, what about the difference in the oil pan? The HT746 seems to be distinctive.
Phils 741 has the updated oil same as the 746 and 748,if you look close you will see that is a adapter that bolts to the standard 740 housing Walter forgot to tell you that part
Well this is a fine kettle of fish. We made it from Quartzsite to Phoenix in heavy rains, stop n go traffic, 65-70 on the freeway. Allison guy from Williams followed us almost the entire way - no issues. Started it up 2 -3 times this morning, no issues. Going in for a trans service and have them diag the trans fluid if they do that. Filters looking a tad aged / bit of rust on the porcelain. Suggested a service. We'll do that plus a couple of other items. No firm diagnosis of what the issue was since it hasn't failed again to be diagnosed. I will swap out all the atec fuses soon back to the original holders. And it turns out that actually voltage was supposed to be approx 26+v on the 3rd fuse position (attached picture). Original information I had received on those values was incorrect from MCI. Correct from the schematic. Still don't really know the exact cause.
Allison guy says they don't much work on these models any more. Harder for them to get the parts. Test equipment older, etc., Only because I was curious about what he was seeing out in the field - so I asked.
If all goes well the next week, will attempt the long grade up to the Prescott Valley area from Phoenix. Though, there's no snow down here!!
Thank you all have have assisted. Such a tremendous group of helpful folks jumped in. My wife & I really appreciate it!!
Kind Regards, Phil