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  #1  
Old October 1st, 2018, 19:11
GPI000 GPI000 is offline
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AW4 transmission help please.

First post, Hey all. 1996 Cherokee Classic 4WD, 4.0. Stock. Transmission will not shift when placed in Drive position. This all started after cleaning the neutral safety switch due to no reverse lights and hard to start. Cleaned switch and installed. Started in park and reverse only and reverse lights worked but no longer shifts. Disconnect TCU and will manually shift fine. Pulled NSS again and verified all was good and still no shift. Replaced with a new unit and no shift. I tried to test all wires as best I can without a good diagram available and checked all connections. I have a second TCU that changed nothing. Grounds at the engine block all cleaned and good. TPS, VSS, and solenoids have also now been replaced with Dealer parts. No check engine lights, engine runs fine. Any ideas? What am I missing?
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  #2  
Old October 1st, 2018, 20:47
lawsoncl lawsoncl is offline
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Re: AW4 transmission help please.

Quote:
Originally Posted by GPI000 View Post
First post, Hey all. 1996 Cherokee Classic 4WD, 4.0. Stock. Transmission will not shift when placed in Drive position. This all started after cleaning the neutral safety switch due to no reverse lights and hard to start. Cleaned switch and installed. Started in park and reverse only and reverse lights worked but no longer shifts. Disconnect TCU and will manually shift fine. Pulled NSS again and verified all was good and still no shift. Replaced with a new unit and no shift. I tried to test all wires as best I can without a good diagram available and checked all connections. I have a second TCU that changed nothing. Grounds at the engine block all cleaned and good. TPS, VSS, and solenoids have also now been replaced with Dealer parts. No check engine lights, engine runs fine. Any ideas? What am I missing?



If it's starting in 1st and not upshifting, check the wiring and the output speed sensor at the rear of the transmission. On a 4wd, the TCU doesn't use the VSS/speedometer in the transfer case. Instead, there is a separate sensor on the transmission itself tucked under the bracket for the xfer case shift linkage on the drivers side. If that's damaged, then the TCU never sees you moving and won't upshift. If you put a meter on it, you should see the voltage bouncing between 12v and ground as the output turns.


If it's trying to start in 4th, then check that the TCU is actually getting power.
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  #3  
Old October 6th, 2018, 15:58
GPI000 GPI000 is offline
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Re: AW4 transmission help please.

Sorry for the long delay. Still testing and no shifting. At pin C3 on TCM connector (transmission output sensor) backprobing shows constant 4.6v while driving. No variation.
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  #4  
Old October 6th, 2018, 16:04
GPI000 GPI000 is offline
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Re: AW4 transmission help please.

And the sensor on the transmission (output speed) behind the bracket is a new dealer sensor.
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  #5  
Old October 6th, 2018, 17:42
lawsoncl lawsoncl is offline
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Re: AW4 transmission help please.

Quote:
Originally Posted by GPI000 View Post
Sorry for the long delay. Still testing and no shifting. At pin C3 on TCM connector (transmission output sensor) backprobing shows constant 4.6v while driving. No variation.

It's one pulse per rev, so you'll want the meter in AC not DC if you're trying to measure it while driving at speed. If you're just in the driveway turning it by hand (ie jack a rear wheel up, trans in neutral, and turn the drive shaft slowly by hand) you can use the DC voltage setting and see if jump between zero and 12volts.
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  #6  
Old October 7th, 2018, 09:07
GPI000 GPI000 is offline
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Re: AW4 transmission help please.

Meter is auto range. Just sees a constant voltage. No CEL with Matco or snap on scanner but cycle the key switch 3times and it flashes 12. No output shaft sensor signal or battery disconnected in last 50 key cycles? Not sure what code 12 it's flashing.
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  #7  
Old October 7th, 2018, 11:28
lawsoncl lawsoncl is offline
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Re: AW4 transmission help please.

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Originally Posted by GPI000 View Post
Meter is auto range. Just sees a constant voltage. No CEL with Matco or snap on scanner but cycle the key switch 3times and it flashes 12. No output shaft sensor signal or battery disconnected in last 50 key cycles? Not sure what code 12 it's flashing.



You should see it do _something_ when the shaft is rotating by hand. You sure it's the correct sensor? As I recall from trying to stick a 1990 output speed sensor into a 1998 tranny that it was too long. The 1998 sensor will fit, but just not work. That's also when I also found out the sensor changed from the simple 1 pulse/rev magnetic switch to the 4 pulses/rev hall effect type of sensor (ie similar to the crank sensor).
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Old October 7th, 2018, 11:29
lawsoncl lawsoncl is offline
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Re: AW4 transmission help please.

Just to clarify, is it starting in 1st and not upshifting? Or is it trying to start in 4th?
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  #9  
Old October 7th, 2018, 11:51
GPI000 GPI000 is offline
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Re: AW4 transmission help please.

Starts and only stays in 1st. Output sensor does register as driveshaft is spun which I had hoped since sensor is new. All positions on NSS test good as far as ohm test at plug. Power to TCM. It's strange.
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  #10  
Old October 7th, 2018, 11:58
GPI000 GPI000 is offline
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Re: AW4 transmission help please.

Sensor is same as what came off. Purchased through local dealer off the VIN. Seems like it just won't see the drive position for some reason. Back probing the TCM with test light swows the stop switch works, 1-2 gear position, and drive gear input if in position 3 on gear selector.
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  #11  
Old October 8th, 2018, 18:31
GPI000 GPI000 is offline
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Re: AW4 transmission help please.

Any one have any ideas?
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  #12  
Old October 9th, 2018, 18:56
lawsoncl lawsoncl is offline
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Re: AW4 transmission help please.

Quote:
Originally Posted by GPI000 View Post
Any one have any ideas?

Resistance on all the solenoids measured good? What happens if you disconnect the NSS altogether? Kinda running out of options here if the OSS measures good, the TCU has power and you're tried a different TCU.
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  #13  
Old October 12th, 2018, 16:01
GPI000 GPI000 is offline
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Re: AW4 transmission help please.

Solenoids measeured good but in a hail Mary I replaced them. Haven't disconnected the NSS but I will try. It just doesnt make sense.
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  #14  
Old October 12th, 2018, 18:47
trippled trippled is offline
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Re: AW4 transmission help please.

Have you checked to see if the tcu is actually commanding the solenoids? It should just supply power to each one. If this happened immediately after the nss cleaning I'd check over your work again very closely
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  #15  
Old October 13th, 2018, 11:41
lawsoncl lawsoncl is offline
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Re: AW4 transmission help please.

Quote:
Originally Posted by trippled View Post
Have you checked to see if the tcu is actually commanding the solenoids? It should just supply power to each one. If this happened immediately after the nss cleaning I'd check over your work again very closely

A bad #2 solenoid is a possibility, but I can't see how it would die after refurbishing the NSS. He mentioned he's already replaced the solenoids, TSS, VSS, and the TCU with no change. We're running out of things to shotgun here. My suggestion to unplug the NSS could help rule out a short in the NSS making the TCU think the shifter is in reverse or 1st.



First Gear S1 on S2 off
Second Gear S1 on S2 on
Third Gear S1 off S2 on
Forth Gear S1 off S2 off
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