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Transmission Power/Comfort problems

S

sadupont

NAXJA Forum User
Location
Easton, Maryland
I've looked through many posts trying to find what I'm looking for, can't seem to get a complete answer. Hoping that a more tech-saavy person can weigh in on this issue.

I've got a 1987 Pioneer, 4.0L, 4wd, Automatic. 148,000mi. Power/Comfort feature does not engage the "power" setting. I've checked the TCU fuse, it's fine. Transmission shifts fine in comfort setting, no unusual issues there. The light on the power/comfort switch does not come on when switched to "power" and there is no noticable difference in shift patterns--in short, it isn't working.

What gives? Could the switch itself be bad? What else should I look for to fix this problem besides the switch? Something else more complicated?

As I mentioned, I've seen some threads on this issue, but nothing particularly direct and I am looking for some more ideas. I'm new to the Jeep, and I look forward to hearing from anyone.

Many thanks.
 
Thank you for the tip on the switch. My next move is going to be to pull that switch out of there and wire a new one in. Have you been through this issue, if so, what would the next thing to check be? Is there something beyond the switch that would be an issue? A control module somewhere? Would the actual TCU go bad and the transmission still shift ok? I am assuming not, but thought I'd ask.
Again, thanks.
 
the difference isn't much, and most people don't notice it.

basically, in comfort mode at almost no throttle, it will enable the TC lockup at 35mph vs 45mph.

when you mash it to the floor, it responds the same in both power and comfort mode.
 
I have the same heep. IMO, No sense in wiring in a new switch. All the later transmissions (90+ I think) are set from the factory to the "Power" shift points. I bypassed the switch so I always have the Power settings on. I would have to pull the switch out to check which connections but...
The switch has 3 wires going to it. I believe I jumpered the bottom wire to the top wire and left them connected to the switch. The light on my switch is always on.
 
stangrcr1 said:
I have the same heep. IMO, No sense in wiring in a new switch. All the later transmissions (90+ I think) are set from the factory to the "Power" shift points. I bypassed the switch so I always have the Power settings on. I would have to pull the switch out to check which connections but...
The switch has 3 wires going to it. I believe I jumpered the bottom wire to the top wire and left them connected to the switch. The light on my switch is always on.
Click to expand...

Actually it's 1991+ models :D . If the tranny is shifting the same in the POWER and COMFORT positions, you either have a bad switch or an open circuit from the switch to the TCU. I haven't hard-wired my switch as it still works, but it never leaves the POWER position, since I get a bit better mileage, and the shifts are crisper. It's very noticable on my rig. Just replace the switch first since it's the easiest.
 
Do your back-up lights work??

If not it's the FUSE under the dash in the panel marked TRANS.

I know it sounds weird but it's true. Betcha a dollar!!
 
Last edited:
OK, I take that back. Mine is a 7.5 A fuse in the lower right hand corner. But that there is the baby that controls the P/C switch AND the reverse lights, or at least the switching for it. When I was standing on my head the fuse actually read SNART (jk). Mines a 90 so can't say what the 91 has. I know they changed stuff tween those years.
:dunno:
But if the 89 doesn't have it I'll still come across with the dollar!!

P.S. My switch did come apart about a month ago (just disintegrated and I just replaced it with a rocker), but I discovered the fuse issue when I fixed my NSS three years ago and my backups still didn't work. When I found that fuse was blown, then my backups worked and my P/C switch lit up and made the difference in the shift points. I'm a mechanic by trial and error and I don't know squat about electronics!!
 
Last edited:
ParadiseXJ said:
OK, I take that back. Mine is a 7.5 A fuse in the lower right hand corner. But that there is the baby that controls the P/C switch AND the reverse lights, or at least the switching for it. When I was standing on my head the fuse actually read SNART (jk). Mines a 90 so can't say what the 91 has. I know they changed stuff tween those years.
:dunno:
But if the 89 doesn't have it I'll still come across with the dollar!!

P.S. My switch did come apart about a month ago (just disintegrated and I just replaced it with a rocker), but I discovered the fuse issue when I fixed my NSS three years ago and my backups still didn't work. When I found that fuse was blown, then my backups worked and my P/C switch lit up and made the difference in the shift points. I'm a mechanic by trial and error and I don't know squat about electronics!!
Click to expand...

Backups work - in the HOs the NSS and the backups are fused in the PDC in the engine compartment, which the earlier Renix models did not have (90 and below). I forget now what the original poster's rig was, but still it's most likely a bad switch.
 
OP is a Renix - 87
No PDC underhood
"Relay Center" only
4 relays + starter
2426393_11_full.gif
 
I appreciate the comments. A couple of my own, getting back to the original questions. First, my backup lights do work. Second, the fuse is fine. (7.5 amp in fuse panel under driver dash) Third, is there another fuse related to the TCU I should be aware of? Fourth, one of the comments said it is not easy to tell the difference between power and comfort: I drove this very Jeep years ago (had been my grandparents since new) and it was dead obvious when you were in power vs. comfort mode. Now, it is clearly not in power mode.

My next move is to replace the switch. If that doesn't work, I don't know what is the next suggestion. Could something else in the wiring be fouled up if a new switch doesn't do the trick?

Again, thanks!
 
sadupont said:
I appreciate the comments. A couple of my own, getting back to the original questions. First, my backup lights do work. Second, the fuse is fine. (7.5 amp in fuse panel under driver dash) Third, is there another fuse related to the TCU I should be aware of? Fourth, one of the comments said it is not easy to tell the difference between power and comfort: I drove this very Jeep years ago (had been my grandparents since new) and it was dead obvious when you were in power vs. comfort mode. Now, it is clearly not in power mode.

My next move is to replace the switch. If that doesn't work, I don't know what is the next suggestion. Could something else in the wiring be fouled up if a new switch doesn't do the trick?

Again, thanks!
Click to expand...

Yeah, it's pretty easy to notice the difference between POWER/COMFORT. These switches going bad are common. You can do a smoke test to verify the switch condition like this:

There are three contacts on the POWER/COMFORT switch, A, B, and C. Pull the plug off from the back of the switch. Use a piece of wire to jumper pins B and C together on the plug. This will put you in the POWER mode; take a spin and see if you are. If you are, the switch is bad. If not, you most likely have an open circuit between switch plug pin B and pin C11 on the TCU.

Shoot me a PM and I can send you the AW4 manual; good diagnostic procedures to tell if the problem is electrical or mechanical. This definitely sounds electrical.
 
If the light doesn't go on, it's either the switch or the trans fuse. It feeds power through the black-yellow wire to B on the switch. In power, it feed voltage to the TCU on C over the tan wire. Sticking a voltmeter on the back of the switch and looking for +12v would tell you pretty quick if it's the switch, fuse or wiring. A bad TCU should not affect whether the light goes on.
 
lawsoncl said:
If the light doesn't go on, it's either the switch or the trans fuse. It feeds power through the black-yellow wire to B on the switch. In power, it feed voltage to the TCU on C over the tan wire. Sticking a voltmeter on the back of the switch and looking for +12v would tell you pretty quick if it's the switch, fuse or wiring. A bad TCU should not affect whether the light goes on.
Click to expand...

Or the bulb itself. :flipoff:
 
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