1088 will not shift, mph gauge not working

[Sweep]

Our 1088 tanker will not shift above second. Can’t shift manually with the buttons either. Mph gauge is not working. It jumps when I put it in reverse. Everything has worked until now. Only work I have done lately is delete the trailer brake valves in the cab and charged two batteries yesterday. Anybody have any quick tips before I dig into the endless tm’s?

 

[Sweep]

Our 1088 tanker will not shift above second. Can’t shift manually with the buttons either. Mph gauge is not working. It jumps when I put it in reverse. Everything has worked until now. Only work I have done lately is delete the trailer brake valves in the cab and charged two batteries yesterday. Anybody have any quick tips before I dig into the endless tm’s?

Also changed the thermostat today.

 

[simp5782]

Bad output speed sensor will default it to 1st gear. Pull the codes on the programmer and see what it says.

 

[Sweep]

Pull the codes?

Bad output speed sensor will default it to 1st gear. Pull the codes on the programmer and see what it says.

The truck does not default to 1st. It goes into 2nd when put into drive. I can shift down to 1st and back to 2nd. How do I pull the codes?

 

[coachgeo]

been discussed in here in good number of threads but search is not always to easy to do in here. Try this http://www.beamalarm.com/Documents/allison_transmission_codes_manual.html should start you in the right direction. This is first one to pop up in google. These key pads are not some super secret military thing..... they are standard allison.

 

[Sweep]

Thank you

been discussed in here in good number of threads but search is not always to easy to do in here. Try this http://www.beamalarm.com/Documents/allison_transmission_codes_manual.html should start you in the right direction. This is first one to pop up in google. These key pads are not some super secret military thing..... they are standard allison.

Thanks I check it out

 

[Suprman]

The truck starts in second. First is low range. Check the codes. Could be speed sensor. It’s on the underside of the trans and is an over the counter allison part.

 

[Sweep]

Thanks for the replies. I got codes from the tranny d1 tranny oil to high and d2 tranny oil sensor failed to high. Can one check the speed sensor for resistance to see if it’s bad?

 

[Suprman]

No it’s a mag pickup. Did you check the trans fluid level? Running warm in neutral. You could have a wiring harness issue. I see that a lot. You should visually inspect the harness it comes out behind the grill drivers sid hump follows drivers side frame rail and then crosses over trans and mates with a pigtail coming off the trans passenger side. Look for dry cracked wiring. Is this a new problem or did you get the truck this way?

 

[Sweep]

I’ll check those things out. Thank you. It’s a brand new problem.

 

[Sweep]

Here are a couple pic of our tanker before it was finished. She came to us as a tractor 1088.

 

[Sweep]

So I put a few things together. The truck stop engine light has been coming on intermittently. I thought it was running a little warm. At 200 the light would come on. It would never get above 210 as it would drop down when the fan would come on. I changed the thermostat to be safe. Now I’m thinking that the trans speed sensor and the trans temp sensor in the transmission may have failed due to the cooler fans never coming on (I’ve never heard them come on). The stop engine was light was coming on for the transmission not the engine. The codes I got from the transmission were transmission fluid to hot and transmission temp sensor failed to hot. Opinions?

 

[Suprman]

Just because the gage said 200 dosnt mean temps couldnt be higher elsewhere. Or the gage could be wrong. The stop
warning is there for a reason. Maybe you overheated the trans. Maybe the pump wasnt circulating the trans fluid properly. I think at this point its an issue that would be best addressed by an Allison dealer.

 

[Sweep]

So what drives the speedo gauge? The trans speed output sensor?

 

[Suprman]

Signal from the output speed sensor fed thru the trans control. Shared with ctis also.

 

[Sweep]

Ok thanks. I pulled the trouble shooting guide for that one and the speed sensor. I’m going to check resistance on these and see. It’s going to the dealer this week anyway, but need to be able to drive it if possible.

 

[Suprman]

I woudnt drive it like that. Could cause more damage. The speed sender usually causes a jittery speedo and erratic shifting when bad. Something else going on.

 

[Sweep]

Is the diagnostics port for the transmission to the right of the collum under dash? Grey rectangular port.

 

[Suprman]

Yes. Do you have wtec2 or 3?

 

[Sweep]

Wtec 2