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Trans won't up shift.

B

btam13

NAXJA Forum User
Location
Des Moines, Iowa
Ok, this is frustrating. I spent 2 hours degreasing the engine compartment on my 1990 xj, 4.0lt and now the trans will not up shift out of 1st gear when in drive. Any thoughts on this?
 
Disconnect the battery for a few minutes to let everything reset. Then give it a try.
 
if it still doesnt work, chances are you got the TPS wet...Go buy a new TPS

Austin
 
Tried to disconnect the battery and see if it would come out of it. Nope. Same thing. Have plenty of torque while accelerating from a stop but no up shift. Then when I let off the accelerator after bringing the RPMs up to about 3000, I don't get any torque to the wheels until I bring the RPMs back up to what I would imagine would match 1st gear or until I get the speed back down. Either way, no torque until the RPMs meet the current speed. It just revs up until it reaches where the RPM would be in what is probably 1st gear at the current speed. I think I either shorted something out or disconnected something. Have no clue which or what though. What now?
 
Sounds like TPS to me... Get any water or degreaser on them and they are gone... TPS reading acuratly is required for the transmission to shift properly...

EDIT: What you are expiencing is what is called "Safe Mode" The transmission will "lock" itself in 1st (sometimes 2nd) gear only until the "problem" is fixed... in your case, you must have gotten the TPS wet ith water/degreaser. The transmission requires input from this sensor and will go to "safe mode" untill it sees the correct input from this sensor... Replace the TPS, unplug battery again, re-connect battery, and problem should resolve itself....

Austin
 
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Thanks. I probably did get water all over it. I washed off the top of the engine. I will try a new tps tomarrow. Are there any tricks to installing a new tps?
 
no pretty simple.... if it still acts kinda funny, dis-connect the battery and follow one of the many* TPS adjustment fourms that are all over this site.... try using the search button on top menu to look for them....

Austin
 
The AW4 trans computer doesn't have a "fail-safe" mode. If it did, it definitely wouldn't be 1st gear as dropping into 1st at speed could be catastrophic. Best bet is 4th or 3rd gear. If the trans computer looses power, you get 4th gear with the shifter in (D).

More than likely the TPS sensor is wet and giving a reading that indicates it's floored and the tranny computer is staying in 1st all the way to redline.
 
lawsoncl said:
The AW4 trans computer doesn't have a "fail-safe" mode. If it did, it definitely wouldn't be 1st gear as dropping into 1st at speed could be catastrophic. Best bet is 4th or 3rd gear. If the trans computer looses power, you get 4th gear with the shifter in (D).

More than likely the TPS sensor is wet and giving a reading that indicates it's floored and the tranny computer is staying in 1st all the way to redline.
Click to expand...
X2
 
So, what is the concensus here? No safe mode? Moisture in TPS causing bad reading? What ever is causing it, the trans is definately not leaving 1st gear and it didn't start until right after I washed the engine. Could unplugging the TPS and blowing out the connectors then reconnecting the plugs fix the problem or is it likely that there is water inside the TPS? If so, can it be blown out? This is my D/D and project, so I really need to get a handle on this. Thanks to all that have helped so far!
 
You are there right? Try blowing the water out of the tps...that might work. I can tell you that over the years I have replaced at least 20 TP sensors for the same problem and no, they were not on the same jeep. That's the way they fail. I don't remember any of them being wet. A bad speed signal will also cause this. It's not a safe/limp mode, it's just what the TCM does with a bad input. If you have a DRB 2 and a renix adapter hook it up and look at the TPS signal...It will most likely read 7 steps.
 
I'm not at the vehicle right now. At work trying to figure out how to not need a ride to work from the wife tomarrow. I don't have a DRB2. Um, what is a DRB2? Is the speed sensor at the back of the transfer case? If so, I doubt that is the problem since I did mess with anything in that area or expose anything in that area to degreaser or water. When I get home I will try to blow out the connections and the TPS and see if that solves the problem. I will need to disconnect the battery so the comp can reset, right? For how long? Anything else come to mind?
 
No. I would think that running with the TPS unplugged would cause all sorts of other problems with the ECM as well as the TCM since both need a signal from the TPS to operate properly. But then, if the TPS is causing a problem with the TCM, why is it not causing any noticable problems with the ECM? Hmmmmm? I wonder if the problem is isolated in the plug that connects to the TCM?
 
The problem is water inside the sealed TPS shorting out the variable resistor inside. Some have put thiers in a convection back oven at 250 F four hours to dry out the sensor and brought them back to life, but from the sound of it you need the DD so just go buy a new one, and then try to salvage the old one as a spare. See the thread "RenX Files" here, by "Ecomike" in advanced search for testing methods, data and calibration details.
 
Ecomike said:
The problem is water inside the sealed TPS shorting out the variable resistor inside. Some have put thiers in a convection back oven at 250 F four hours to dry out the sensor and brought them back to life, but from the sound of it you need the DD so just go buy a new one, and then try to salvage the old one as a spare. See the thread "RenX Files" here, by "Ecomike" in advanced search for testing methods, data and calibration details.
Click to expand...

If the TPS is sealed, how does water get in there?:huh: LOL. But really, I am gonna try to blow out the pigtails and start cleaning up grounds. I just think that since it seems to be affecting the TCM only, it would likely be shorting in the pigtail going to the TCM from the TPS. Just my logic. If it was in the sensor it"s self, wouldn't it affect more than just the TCM?
 
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Ok, tried to blow out the pigtails. No change. Tried blowing out the TPS. No change. Pulled the TPS and have a replacement being brought in from across the state tomarrow since no store in town stocks one except for the dealer maybe, but I won"t even check there because I don't feel like paying twice the price. While I wait I guess I will try to find a thread on testing the TPS sensor.
 
When you unplug the TCU pigtail of the TPS, should the trans be able to be shifted through the gears manually? If so, at what RPM would the trans shift at? I tried this on mine but only took the RPMs up to 3000 and then tried to shift it manually. No shift happened. Thought this might isolate the problem to the TPS for confirmation.
 
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