Really good Allison problem..see what you think

[rgrimard]

Ok guys...here comes a good problem with an Allison 748 ATEC in a 102c3. While getting fuel, and in neutral, the trans went into the dreaded "don't shift" mode and would not clear ...had to have it towed home. Once home, I checked the test switch..which the "check trans" light flashed a 54 code...a code which calls several solenoids into question (I have the troubleshooting manual) or even a broken or shorted wire from the ECM to the tranny. Unplugged the J connectors from the ECM and checked all solenoids for an open. Checked all wires in the harness ... All checked good. Just to make sure... I next dropped the pan and physically checked each individual solenoid for an open...all checked good. Checked for a short on the connection board between connectors...all checked open(good). I checked for continuity from the individual terminal connectors on the interface board to the female Deutch plug that plugs into the pass trough bulkhead connector..all good. (I unplugged the battery source to the ATEC, Battery is fully charged, checked all fuses, reset all connectors to the ECM, shift selector, tranny,) I still have the 54 code. I feel so defeated. Any in-site?
Ray

[luvrbus]

? does the speedometer work most 748's use a magnetic type 1 speed sensor that works off the speedometer, wheel or mounted on the tail shaft on the transmission

[Scott & Heather]

Hey ray are you the guy who had the mice chew through his wiring harness for his trans?


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[rgrimard]

no i didnt have any mice issues.

[rgrimard]

wow...thats funny you should ask about the speedo it actually stopped working about 9 months ago. we have been using the gps for speed reference. would that be a possible issue here ?

[rgrimard]

luvrbus...would a bad speedo signal cause a code 54? if so...how do i clear the fault...replace the sensor? any checks i can do prior to relacement. ive got about 100 hours in this problem...a couple more toward a fix would be great. thanks for the replys guys.
Ray

[blue_goose]

After you dropped the pan, did you replace the oil in the transmission?  If the speed sensor on the tail shaft was bad the transmission would not shift a all.
Sounds like about time to have the problem checked with the Allison computer program.
Jack

[Bill Gerrie]

I friend of mine in Alberta Canada had the exact same code. All tested good and if memory severs me right he had to replace the ATEC computer. Maybe email him and see what he did. He is the kind of guy that would be more then willing to help you.
joe.padberg@canadasurfs.ca

[luvrbus]

Find out where the speed sensor is located it may be on the wheel or on the speedometer cable the type 1 sensor is a magnetic sensor.I don't see many mounted on the tail shaft.
Sad part is Allison has dropped support for the ATEC 748 so you need to call around and find a dealer willing to help you clear the code.
They will shift my friend Joe from Canada had the same problem and had to replace the computer then all was good

[rgrimard]

Thank you guys. I will do all and email Joe. Luvrbus, I have a friend of mine that is stopping by with a Prolink to see what he can see. He is a transit (actually the head guy at Volusia County Transist) so we will see if it shows anything. But just to clarify, the speed sensor (or a faulty on) could cause a code 54?
Ray

[rgrimard]

update: my friend who is the head mechanic for the local city transit co. took a look at my problem, checked it with his Pro Link and found no additional error codes. he then checked the J1 connector and found 6 of the plug"s female ends flattened to the sides so no connection...or the ECM could not see it. i have a rack of pins that i will be replacing the questionable ones with tommorow. ill keep you posted.
Ray

[Scott & Heather]

Do keep us posted ray.


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[Geoff]

Damn computers.  9 out of 10 times it is a bad harness connection.  I keep looking at Harbor Freight for a tool set to clean and expand the male and female connectors.  Or does Snap-On have it already?

--Geoff

[luvrbus]

Damn computers.  9 out of 10 times it is a bad harness connection.  I keep looking at Harbor Freight for a tool set to clean and expand the male and female connectors.  Or does Snap-On have it already?

--Geoff

Watch what you doing and pins don't bend  lol I bent a pin on the 4L60 in the Envoy only took me 3 days to find the problem

[rgrimard]

Will do. I've got the extractor tool and crimper. The pins are the same as used in DDEC applications. Fingers crossed.
Ray