Speedo inop

This topic contains 9 replies and was last updated by andy-2 10 years 2 months ago
February 9th, 2011 12:09am
We have a 2004 CE300 international school bus. It has a DT466 non EGR and a Allison 1K2K. The driver says the speedo is erratic. On a test drive, at first the speedo does not work then starts working but reads all different kinds of speeds it appears to work till you come to a stop then as you drive along it is inop for awhile. The transmission shifts good and codes 141 and 142 come up on the computer but go to inactive when the speedo is working. Our buses are limited to 62mph and this bus still has its limit. We have inspected the exciter ring in the trans its ok, the cluster was swapped, the speed sensor was swapped, the engine ECM was swapped, and the trans ECM was swapped, and the wiring traced and ohmed and no resolve was found. The Allison program on our computer shows no codes and all sensors working. We are having trouble finding the correct wiring harness schematics and have been consumed so deep that we are grasping at what is left of our hair. Thanks in advance for the help.
February 9th, 2011 3:58am
I would strongly suggest you ask this question to John Waylen aka the "School Bus Mechanic" on this site in the menu at the bottom of the list. If anyone can answer this question it's John. We are very fortunate to have his expertise on Mechanics Hub.
February 9th, 2011 6:54am
I am wiling to bet you have either a bad ground or a bad connection or a broken wire some place. That would give you the crazy readings.
February 9th, 2011 6:57am
The trouble is to find it I would try using a ground jump wire on the sencer and test drive it if that dont work run new wires from the speed senser to the computer. even a temp one to try it on a road test
April 8th, 2011 9:05am
What was the resistance on your speed sensor wiring? It doesn't have to be much to create problems. We've replaced a lot of wiring on our Allison harnesses. Our stock room has a roll of coaxial wiring for this purpose. It would be worth the time to try it. Have you found the problem since you've posted or tried anything else?
May 18th, 2011 4:10pm
Would be nice to know what happened & if it got resolved. I come across speedo problems quite often on different vehicles and a lot of the time it's down to nothing more than bad connections, a few Ohms can make a lot of difference.
May 18th, 2011 11:18pm
sorry for the delay we did get it fixed. The problem was that the transmission computer was wrong for that trans. Some knuckle head had swaped it out and not said anything to anyone. we have alot of that here because of the low quality training and mechanical background so we get alot of guessers
May 19th, 2011 12:12am
Glad to know you got it sorted out, unfortunately I seem to come across more & more of this sort of thing. A lot of Auto Electricians & Mechanics don't even seem to know the basics of fault finding any more & just change parts in the hope they eventually fix the problem.
May 19th, 2011 4:43pm
And that makes the job 50 times harder than it should be! Last week I got to attend the Thomas bus class in Highpoint NC. We got alot of information and got to tour the Thomas manfacturing plant for the C2 and the HDX. These buses are going to be the wave of the future being more like a car/truck rather than a prehistoric beast with wireing everywhere. But on the flip side of that I see alot of the older techs falling behind even more and unwilling to change or learn the new ways. Are you a bus Mechanic? How many in your fleet?
May 19th, 2011 6:00pm
Hi mate: No not a Bus mechanic although I used to work on a lot of Buses at 1 time, i'm actually a self employed Auto Electrician working for different Garages / Hire outlets so see a lot of different equipment. Unfortunately more & more seems to have already been "looked at" & as with your problem you very often don't get told of this until you've pulled out what little hair you've got left:lol: . Your lucky you got some training. Over here as an Independent, manufacturer training is'nt available to me & a lot of the private training thats available is'nt worth the time / effort of doing it. I seem to spend a lot of time on the Internet studying stuff just in case I come across it, Thats why I love this site ther'es so much info from people who actually do the job. Totally agree with you about some of the older guys not wanting to change or learn, but we are'nt all like that(Maybe i'm just naturally nosey). I see a lot of Mechanics etc who can't even do basic fault finding on a car using a test lamp let alone a DMM or Scope, so God help them if they came across a Coach or Truck. Sounds very much like what your coming up against.


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