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Auto trans won't shift

jabbo-1

NAXJA Forum User
Location
galveston
I have a 95 cherokee sport, 6 cyl, auto. The transmission won't shift unless I pull the fuse in the fusebox under the hood, then I can shift it manually. Is there some kind of electronics that controlls the shifting ?
Otherwise the trans. stays in drive only with the fuse installed...
 
Well, the AW4 in your 95 is electronically controlled.

Not 100% positive on a new-fangled rig like yours, but the TCU--transmission control unit--is located under the dash on the passenger's side or under the dash on the driver's side between the steering column and the knee panel. Either way, there should be a 10 amp fuse on a yellow wire leading to the TCU--that is the power supply. Normally(?) the fuse in the fuse panel something like 7.5 amps has another function.

Check the inline fuse on the yellow wire to see if it is blown.

Unplug the TCU and drive it shifting manually--you will have 1st in 1-2; 3rd in 3; 4th in D; reverse, neutral, and park. If everything shifts Ok manually, then the problem is definitely electrical.

Electrical problems for the AW4: bad TPS--throttle position sensor; throttle body pressure cable needs adjusting; blown 10 amp fuse to TCU; bad TCU; bad solenoid(s) in the transmission; bad NSS--neutral safety switch (it has more functions than safety); and the wiring between all of the preceding.
 
Thank you very much.....I bought a manual from O'reillys, and it doesn't go into any specific details on this subject. I will check all this out the first of next week !
 
I bought a manual from O'reillys, and it doesn't go into any specific details on this subject.

Your manual is probably a Haynes or a Chiltons? They are very generic and cover a number of years.

If you want a comprehensive manual, try to find a used factory service manual or FSM (ebay has them sometimes). They can be kind of spendy but they are specific to your year XJ and have all repair information you'll want in there.....
 
So the symptoms are that it tries to start in 4th gear with the shifter in (D)? In order of likely causes, I'd say - a blown trans fuse, bad shift solenoid, or bad trans computer.

The shifting is controlled entirely by a seperate computer. On a 95, the trans computer (TCU) is under the passenger side of the dash. There is no inline fuse in the wiring harness like the older non-HO setup. Some troubleshooting with a meter should point you straight at the problem. http://www.transonline.com/transdigest/magazines/1997-10/Shift%20Pointers/index.html has a great writeup for doing some basic diagnostics with a meter. In particular look for power on the red and yellow wires, and the shift solenoid resistance readings.

If you don't have a meter, get one. You'd be surprised at how handy they can be. Radio Shack or Sears have decent ones for about $20. The el cheapo Harbor Freight oes work pretty well as well. I bought a whole bunch of them when they were on sale for $1.99 each. I have one in each car and give them away to friends who need one.

Worse case, drive on up here and I'll look at it for you. Just bring some of that snow with you as we've got nothing but mud in the yard. Normally I've got about 2-ft of snow still piled up in Feb.
 
The el cheapo Harbor Freight does work pretty well as well. I bought a whole bunch of them when they were on sale for $1.99 each. I have one in each car and give them away to friends who need one.

Good advice Lawson as usual.

Meters for $1.99? Too rich! :yelclap: Maybe should hand them out to trick-or-treaters to promote DIY repairs at that price.

I so agree with you though. If you are doing ANY repairs on your vehicle, you need a meter. So many things on an XJ can be diagnosed with a meter and a manual. Meters aren't as difficult to use as you might think. Many come with an instruction book and there are lots of good resources on the web.
 
Those DMMs for $1.99 were a steal. I still have two new ones in the roll cabinet after using five for stocking stuffers a few Xmases back.

I like the Actron/Sun DMMs with the Tach and audible continuity testers built in. They can be had off of eBay, on occasion, for about $30.
 
Good advice Lawson as usual.

Meters for $1.99? Too rich! :yelclap: Maybe should hand them out to trick-or-treaters to promote DIY repairs at that price.

I so agree with you though. If you are doing ANY repairs on your vehicle, you need a meter. So many things on an XJ can be diagnosed with a meter and a manual. Meters aren't as difficult to use as you might think. Many come with an instruction book and there are lots of good resources on the web.

They looked like this one. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=98025. I also got some that were yellow and didn't have the on/off switch so you had to spin the dial back to 'off' each time. The only issue I noticed is that they start reading way off when the battery gets real low. Other than that, they decent cheap meters.

I've got a nice meter for the workbench that does capacitance, diodes, inductance, etc. I use that one extensively repairing electronics.
 
I sure appreciate all the helpful guidance. I have deduced the problem down to the TCU unit. Have ordered another one and should be automatically shifting next week !
 
I sure appreciate all the helpful guidance. I have deduced the problem down to the TCU unit. Have ordered another one and should be automatically shifting next week !

Couldn't source one at the local salvage yards?
 
May I be so rude as to hijack this thread since the OP seems to have solved his problem?

My 96 has very similar symptoms to the OP's 95 except that mine does not require pulling the fuse in order to shift manually. So when I put it in D it starts out in 4th. Technically, it hits 1st for a split second before going into 4th. Shifts fine manually (skips 2nd, obviously). This started out as an intermittent problem months ago and in the last few weeks has become constant.

I replaced the TCU with a JY unit back when it was intermittent, but it didn't fix it. Then once it became constant, I swapped in a second JY TCU...no fix. The 10A fuse under the hood has been good the whole time. I had kind of ruled out solenoids because it shifts fine manually. What am I missing here? I would appreciate some advice from the AW4 experts. Thanks.
 
1. Have you adjusted the throttle body pressure cable?

2. Have you tested the TPS?

3. Have you adjusted the NSS? (It is more than just a safety switch.)

4. Have you adjusted the shift cable?

5. Have you unplugged the TCU and tried shifting manually? You would have 1st in 1-2; 3rd in 3; 4th in D; reverse, neutral, and park. If you don't, your problem is hydraulic/mechanical.
 
Thanks for the help. Answers in red.

1. Have you adjusted the throttle body pressure cable? Yes, shifts were slightly hard, but very smooth after adjustment. But didn't help the lack of electronic shifting.

2. Have you tested the TPS? No, but it was replaced about a year ago. If it needs to be tested, I'll have to buy a meter and learn how to use it. Or I have a spare believed to be good that I could swap in if necessary.

3. Have you adjusted the NSS? (It is more than just a safety switch.) Yes, I double checked it again yesterday. Starts in both park and neutral and my reverse lights are working. Safe to assume it's adjusted correctly?

4. Have you adjusted the shift cable? No. What is this?

5. Have you unplugged the TCU and tried shifting manually? You would have 1st in 1-2; 3rd in 3; 4th in D; reverse, neutral, and park. If you don't, your problem is hydraulic/mechanical. No, I haven't unplugged it, but the behavior you describe is exactly what I have with it plugged in. Should I try it unplugged as well?
 
If you are getting exactly what I described in line 5, then you have an electrical issue. Either the fuse is bad, the harness is bad, or the TCU is bad.

You replaced the TCU, so unless you have two bad TCUs then you are left with a bad fuse or bad wiring. Pop in a new fuse and see what happens. And buy a digital multimeter, you need one.
 
Yes, that's exactly what I'm getting. I will add that at highway speed in D, it will kick down from 4th to 3rd with throttle input only. But then when I stop, it doesn't downshift into 1st.

I double checked the 10A fuse in the PDC and it's good. Are there any other fuses in play here? I'll go buy a digital multimeter tomorrow if there's something I could check that would help with diagnosis.
 
If you are getting exactly what I described in line 5, then you have an electrical issue. Either the fuse is bad, the harness is bad, or the TCU is bad.

You replaced the TCU, so unless you have two bad TCUs then you are left with a bad fuse or bad wiring. Pop in a new fuse and see what happens. And buy a digital multimeter, you need one.
Could also be solenoids like you said before - or a wiring harness issue.

Is torque converter lockup working properly? If you press on the gas at highway speeds the tach should not move much at all, even though the engine works harder and you accelerate. If you let your foot off the gas it should hang at the same RPM for a few seconds and then drop down a bit. If it randomly blips higher while you're cruising, or shoots up when you give it some gas, the torque converter isn't locking up. I believe with the symptoms you list it should not be locking up, though I'm not sure. Either way it's another data point for the tranny wizards.
 
I had kind of ruled out solenoids because it shifts fine manually.

Pulling the fuse and shifting manually eliminates a mechanical problem. It doesn't eliminate a solenoid issue You could still have a bad solenoid. Get a meter and go to http://www.transonline.com/transdigest/magazines/1997-10/Shift%20Pointers/index.html for info on how to measure the solenoid resistance and power to the trans computer.

96 XJ Sport said:
Yes, that's exactly what I'm getting. I will add that at highway speed in D, it will kick down from 4th to 3rd with throttle input only. But then when I stop, it doesn't downshift into 1st.

This does sound like a bad solenoid.
 
Is torque converter lockup working properly?

Strangely enough, the TC is locking MOST of the time. And when it doesn't, a manual shift to 3rd and back to 4th generally causes it to lock again. To add to the bizarre, sometimes when holding in 3rd manually, the TC will lock in 3rd. I kind of like that "feature" because it works well with my 31s and 3:55 gears for moderate highway speeds, but I know it's not supposed to lock in 3rd.

Pulling the fuse and shifting manually eliminates a mechanical problem. It doesn't eliminate a solenoid issue You could still have a bad solenoid. Get a meter and go to http://www.transonline.com/transdigest/magazines/1997-10/Shift Pointers/index.html for info on how to measure the solenoid resistance and power to the trans computer.

Just went out at lunch and bought a digital multimeter at AZ. Never used one before, but surely I can learn. I printed that linked article and will give it a go. Thanks for the help guys.
 
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