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AW4 transmission help please.

GPI000

NAXJA Forum User
Location
South Carolina
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?
 
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.
 
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.
 
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.
 
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.
 
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).
 
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.
 
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.
 
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
 
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
 
Some more rambling thoughts...


I think a 1996 still has a reed switch for the output sensor. If it has power to the sensor plug, then it's a switch that closes and pulls the voltage down to ground once per rev. That's easy to test with a meter and turning the output slowly by hand. Going fast with a meter attached will probably just look like an a/c voltage. Using the DC scale on the meter, that 4.6 volts sounds about right.



If it's the newer inductive pickup (which I think didn't change until 1998), then I don't believe it will have power to it. You'll see a a/c voltage spike as the output shaft turns - it's roughly proportional to the rpm so you'll have to spin the output reasonably quick to see it. It gets up to about 30-volts a 3000 rpm as I recall. When I was scoping the output on the 1998, I just put the xfer case in neutral and the trans in gear.
 
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

Never said the solenoid is bad. I said to see if the tcu is commanding power to the solenoid. If it's not supplying power it's an electrical problem and not mechanical.
 
Well, definitely an electrical gremlin. Going to have to pull harness and go through it. Can't see any other option causing this than a wire. Thank you for all the ideas so far. Helps to verify what has been done this far.
 
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