Stranded again

Scott & Heather · January 01, 2019, 11:39:58 AM

My VSS is fragging out which, of course, makes the ATEC system go into "Do Not Shift" mode. So I'm stuck on I-75 south on the shoulder just inches from the white line trying to get her going again. I'm in neutral. I reset the codes using my laptop an DLINK interface but no dice. Still flashing DNS. I also disconnected touchpad and waited a bit and reconnected it but that didn't do it. Can someone please tell me exactly where this Vehicle Speed Sensor is located? I need to address this.

chessie4905 · January 01, 2019, 11:44:30 AM

If no help, try a Google on speed sensor location for your model transmission. Should be near trans output shaft, although some electronic trans may have two or three in same general area.

Scott & Heather · January 01, 2019, 11:52:00 AM

Thanks...I've done this a little without any definitive results that I could understand. Does anyone know of a way to force shift an ATEC trans just so I can get off the road? This is dangerous. I'm about to call a wrecker.

Jon · January 01, 2019, 12:48:06 PM

You should be able to get it in drive. It will not shift out of 1st, but you should be able to do 10 or 15 MPH to get you in a safer spot.

I agree with the speed sensor being the likely issue. It is a common failure. I think there are 2 sensors on the driver's side of the transmission and a local Allison dealer probably has them in stock. You will need to provide the transmission serial number. Once you get the sensor you can't screw up and put the new one where it does not belong because although they are near one another and look similar I think the plug or mounting method will keep you from putting in the wrong location. I think the speed sensor that might have gone bad is the one closest to the engine.

luvrbus · January 01, 2019, 12:58:51 PM

Not much help but if you cannot get the 700 series ATEC to go to limp mode I have no Idea how to made it engage,they are in their own world

Scott & Heather · January 01, 2019, 02:10:42 PM

Thanks for the thoughts. It is not in limp mode. It will not shift at all. Stuck in Neutral. I've tried everything. Going to get towed into a campground two miles down the road and will continue to troubleshoot. It gave me a speed sensor fault code just as it failed. I saw it on my dlink screen. And at the same time my speedo stopped working and the trans went into fault mode.

buswarrior · January 01, 2019, 02:14:48 PM

Remove and replace with a 740 with air shifter, for ease of retrofit...?

Someone had to type it...

Glad you got it cleanly off the road, and didn't meet the bear with fur...

happy coaching!
buswarrior

chessie4905 · January 01, 2019, 03:22:04 PM

I see where someone on Facebook said to remove speed sensor and clean off end and reinstall. Did you try that?

Scott & Heather · January 01, 2019, 03:28:59 PM

First time ever getting towed into a campground. I could get used to this. Will get down and dirty tomorrow troubleshooting

thomasinnv · January 01, 2019, 03:39:53 PM

You should be able to see the speed sensor on the side of the trans (should be a 2 wire most likely), there may be 2 or 3 of them. Yours is different from my B500 but on mine there is a sensor on the input turbine, one in the middle and on toward the tailshaft. Mine gave me all kinds of fits a few years ago until I finally found a break in a wire at the plug on the output speed sensor. Ohm the harness from the sensor to the tcm while moving the wires around to make sure its not a wiring issue. You can usually get the sensors next day at napa.

DoubleEagle · January 01, 2019, 05:03:27 PM

At least you are down South and not in snow or slush, or stuck in downtown Atlanta in the middle of traffic.

Scott & Heather · January 01, 2019, 08:49:01 PM

Quote from: thomasinnv on January 01, 2019, 03:39:53 PM
You should be able to see the speed sensor on the side of the trans (should be a 2 wire most likely), there may be 2 or 3 of them. Yours is different from my B500 but on mine there is a sensor on the input turbine, one in the middle and on toward the tailshaft. Mine gave me all kinds of fits a few years ago until I finally found a break in a wire at the plug on the output speed sensor. Ohm the harness from the sensor to the tcm while moving the wires around to make sure its not a wiring issue. You can usually get the sensors next day at napa.

Awesome. Good info here. Thank you. I'll dig around tomorrow in the light of day and see what I can find. I'm hoping to get this fixed before the end of the week.

luvrbus · January 02, 2019, 02:03:19 AM

a bad speed sensor shouldn't prevent engagement on the 700 if you have power to the pad and ECM it should go to the limp mode ,the pad is powered by a fuse in the upper corner in the panel under the drivers window,the ECM fuses are in the battery compartment on a MCI good luck

DKO · January 02, 2019, 04:30:15 AM

I hate that for you Scott. I am no help to you, but we are following along closely.

Davy

Scott & Heather · January 02, 2019, 05:30:38 AM

Problem Solved.

Found the speed sensor and followed the two wires to the harness where one of them was corroded and broke in half. I temporarily spliced it back in and the trans issue was gone. So I'm now properly splicing and soldering the connection so we don't have this issue in the future and we should be on our way before noon. Thanks to all who helped. The photo shows the wiring where it enters the harness. I had to peel and cut the harness shield (carefully) so as to get to the proper wires, that's why it looks like a rat chewed it up.