XJ problems after many tries to fix...

[Earthling1984]

Hello all. So I have a 1998 Jeep Cherokee automatic. It hasn't shifted into 1st gear for some time automatically, and I have been driving by putting it into 1/2, 3, D. It drives fine, but I failed emissions testing due to these transmission codes (P0700, P0756, P0758).

My Cherokee is almost fully redone, from all new sensors (o2's, TPS, Map, etc), new cat, new muffler, new tune up, and now I just put in 3 new transmission solenoids as suggested by this forum page:
http://www.naxja.org/forum/showthread.php?t=987463

I was having the same problem as talked about in thread above; however, putting in new solenoids did not fix my problem, my Jeeps check engine light is still on, and it still isn't starting in first gear. I don't know what else to do...

I randomly went into the driver wheel well and took a couple pictures. I am unsure what the 'GALLS' thing is (as shown in picture) and why it is on the 'off' position. I am scared to flip the switch, I don't know what it is. I also noticed there is a wire that is unplugged just hanging there, but, I don't know where it goes, it doesn't seem to reach any plug / all plugs seemed full.

Any insight?

 

[beatittofit]

I just looked on the web-site. it's a controller for lights. Did your Jeep have some kind of lighting on it at some time? Maybe construction, security or even a pilot vehicle for oversize loads.

 

[Earthling1984]

I purchased it used. It does have a light bar on roof (that works with the switch under turned to the O position). It also has a hitch on back, but I don't see any wire harness going to the rear for connecting to a trailer. But ok, so that is just lights, maybe that extra plug that isn't plugged in is for connecting another wire to to connect to a trailer? Could be I guess. I can't figure out what is damn wrong with the shifting which sucks still

 

[Earthling1984]

I purchased a new TCU (well used, but supposidly tested and working) off ebay. Tried it, still not going into first... AHHH

 

[kastein]

The P0758 code is the clue you need here. The TCU was never faulty. The solenoid may not have been faulty either but at least it's not now. What's likely at fault is the wiring harness that is in between them, which unfortunately is a fairly major one, so you're going to want to work carefully with a meter (don't just go hacking into it and messing around, measure at each connector, etc until you find the issue) and then repair as necessary.

Go to http://bbbind.com/free_tsb.html, click the wiring diagram button, enter your make/model/year and then select transmission control system and find the wiring diagram that has the color codes and pin numbers for the wire from the TCU to shift solenoid B (which may be a numbered solenoid in the wiring diagrams not a lettered one, I forget.) Start tracing that color wire from connector to connector with a meter and you will eventually find a break between two of them or a short to ground. At that point, just fix it and it should work fine.

XJs are getting on in years now and wiring harness issues are getting more and more common. The truly troublesome harness problems showed up a decade ago, but the less common issues are now coming up more often. This isn't one I'm overly familiar with, so you may have just gotten unlucky.

A lot of people - you included - are treating harnesses like black boxes that magically work no matter what, and assuming sensors and control modules and such are the problem. That's usually a fairly valid assumption, but once you're working on an older, high mileage vehicle, you need to think about things pretty critically and pull out the meter before you go for your credit card and get new parts, or you'll just end up shotgunning expensive stuff at it until you succeed by luck. I've seen people blow thousands on diagnostics and replacement sensors and modules with a mechanic only to find out that a dirty connector or intermittent wire was at fault the whole time.

 

[Digger87xj]

The P0758 code is the clue you need here. The TCU was never faulty. The solenoid may not have been faulty either but at least it's not now. What's likely at fault is the wiring harness that is in between them, which unfortunately is a fairly major one, so you're going to want to work carefully with a meter (don't just go hacking into it and messing around, measure at each connector, etc until you find the issue) and then repair as necessary.

Go to http://bbbind.com/free_tsb.html, click the wiring diagram button, enter your make/model/year and then select transmission control system and find the wiring diagram that has the color codes and pin numbers for the wire from the TCU to shift solenoid B (which may be a numbered solenoid in the wiring diagrams not a lettered one, I forget.) Start tracing that color wire from connector to connector with a meter and you will eventually find a break between two of them or a short to ground. At that point, just fix it and it should work fine.

XJs are getting on in years now and wiring harness issues are getting more and more common. The truly troublesome harness problems showed up a decade ago, but the less common issues are now coming up more often. This isn't one I'm overly familiar with, so you may have just gotten unlucky.

A lot of people - you included - are treating harnesses like black boxes that magically work no matter what, and assuming sensors and control modules and such are the problem. That's usually a fairly valid assumption, but once you're working on an older, high mileage vehicle, you need to think about things pretty critically and pull out the meter before you go for your credit card and get new parts, or you'll just end up shotgunning expensive stuff at it until you succeed by luck. I've seen people blow thousands on diagnostics and replacement sensors and modules with a mechanic only to find out that a dirty connector or intermittent wire was at fault the whole time.

Great link and advice!

Unfortunately, most junk/recycle yards hack the harnesses pulling other components and never had the foresight that older vehicle harnesses would be worth their time to keep intact.

 

[jap813]

just had the same issues on a 93 and the last thing i checked turned out to be the issue. try unplugging your brake light switch and see if the issue is resolved. Mine was partialy cracked open and was not letting the tcu to unlock the torque converter. possibly cracked from foot going to high on brake pedal, but unplugging it made the trans work perfectly