SLT 4.2l 2wd. Where do the two vacuum lines go from the top of transmission?

Some Chrysler ,Jeep and Dodge vehicles have ttye pressure sensors calibrated to the vevicle,so therefore if you change the
tyres to a different type you will need to take your vehicle to a C.J.D.
service department to have the computer of your car re-programmed to accept the new tyres

The vacuum actuator should move by hand without vacuum applied. You should also be able to see it move if you have someone switch the transfer case into 4hi/lo from 2wd and then back again. There is a vacuum switch on top of the transfer case that locks vacuum once the encoder motor engages the transfer case to lock the front axle into position, and then releases the vacuum once the encoder switches back into 2wd mode allowing the front axle to decouple. If you aren't getting vacuum, first check your vacuum lines for leaks, then check for vacuum coming from the transfer case when it's in 2wd mode.

Operationally vacuum shifts the front axle between 2WD and 4WD mode. The GEM ( Generic Electronics Module ) applies ground to the solenoid needed for the mode selected on the switch ( for ESOF ) or when the transfer case shift lever is moved ( MSOF ).The contact plates in the transfer case signal the GEM that the transfer case is engaged, and the Vacuum solenoids need to be activated ( either 2WD to 4WD or 4WD to 2WD ).

Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
- If it turns it is a problem with the transfer case.
- If it doesn't it is a front axle engagement problem ( this is what you seem to have, the transfer case is engaged and will drive the front shaft mine was a key on engine off test ).

- If the front drive shaft does not turn :
•With the truck running ( with front wheel back on the ground ), switch from 2WD to 4WD and back again, the vacuum shift motor should move the lever on the front axle.

-- If the vacuum shift motor does not move:
1.Check for vacuum on the lines while shifting between modes. Pink vacuum line is 2WD mode, Light Blue vacuum line is 4WD.
2.Check the fuses for the 4WD system and the solenoids.
3.Check the vacuum lines from the vacuum shift motor to the solenoids on the firewall.

4.Check the vacuum lines from the solenoids to the vacuum reservoir box behind the battery.
5.Check the vacuum reservoir box for cracks.
6.Typical solution is the vacuum lines ( to the solenoids or to the vacuum shift motor ) are cracked or the vacuum shift motor has a cracked diaphragm and has water in it.
7.Could be the shift plate contacts in the transfer case are corroded / not making good contact, and not activating the solenoids.


Usually the case is cracked vacuum lines from the solenoids, the next common is a cracked vacuum reservoir box, and 1 time I have seen the mount for the vacuum disconnect motor broken ( motor floating free so it could not push against the axle )

Vent line for the rear axle housing / breather vent

Operationally vacuum shifts the front axle between 2WD and 4WD mode. The GEM ( Generic Electronics Module ) applies ground to the solenoid needed for the mode selected on the switch ( for ESOF ) or when the transfer case shift lever is moved ( MSOF ).The contact plates in the transfer case signal the GEM that the transfer case is engaged, and the Vacuum solenoids need to be activated ( either 2WD to 4WD or 4WD to 2WD ).


Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
- If it turns it is a problem with the transfer case.
- If it doesn't it is a front axle engagement problem.

- If the front drive shaft does not turn :
•With the truck running ( with front wheel back on the ground ), switch from 2WD to 4WD and back again, the vacuum shift motor should move the lever on the front axle.
{ picture of shift motor }
-- If the vacuum shift motor does not move:
•Check for vacuum on the lines while shifting between modes. Pink vacuum line is 2WD mode, Light Blue vacuum line is 4WD.
•Check the fuses for the 4WD system and the solenoids.
•Check the vacuum lines from the vacuum shift motor to the solenoids on the firewall.
•Check the vacuum lines from the solenoids to the vacuum reservoir box behind the battery.
•Check the vacuum reservoir box for cracks.
•Typical solution is the vacuum lines ( to the solenoids or to the vacuum shift motor ) are cracked or the vacuum shift motor has a cracked diaphragm and has water in it.
•Could be the shift plate contacts in the transfer case are corroded / not making good contact, and not activating the solenoids.


- If the front drive shaft turns:
•For ESOF system
-- Check the fuses for the transfer case, engine compartment fuse panel, 17 & Cab fuse panel fuses 13 and 23 ( verify with owners manual, 97-97 & 99-03 MY can be slightly different on some items ).
-- Try hitting the transfer case with a dead blow hammer ( do not use a metal hammer, it can damage the transfer case ) to see if the transfer case shift motor is hung up .
-- Check the transfer case connector, to make sure the connector pins are clean and making good contact.
•For MSOF systems
-- Check that the shift linkage on the transfer case is moving when the lever is moved from 2W to 4H and 4L.

With the engine running, transmission in neutral, foot on brake, push the 2wd button. If it doesn't respond, try the same thing with the engine off, key on. If it's still in lo range, you may have to get under the truck and shift the linkage manually. While you are under there, check the electrical connections and vacuum lines.

indicates that the vacuum actuator is not shifting the ratios when the vacuum level drops off
when a certain vacuum level is reached in the inlet manifold, the actuator makes for the change and if that is not working properly then what you describe happens
run the fault codes first to determine if other sensors like the VSS, TR or TCM are fully operational as well
but as the transmission is changing well after that , it will not be a transmission problem

Lift and support the front of the truck so the front wheels are off the ground.
Key on, engage 4x4 and try to turn the front drive shaft.
If it turns it is a problem with the transfer case.
If it doesn't it is a front axle engagement problem.

There are the two lines that operate the diaphragm on the axle. Facing the truck, the right solenoid (pink & black lines) is activated to disconnect the axle and go back into 2WD. The left solenoid (blue & white lines) lock the axle into 4WD

you'll have to get a vacuum source like a Mighty-Vac hand pump and apply vacuum to the pink and blue lines, one at a time. If one leaks down you'll have to check the line, including the diaphragm, to locate the leak. If vacuum was held, reconnect the bottom half of the line "connector" (black & white lines) to the solenoids and crank the truck. Switching from 2WD to 4WD and back verify each time that there is vacuum on the top nipple of the activated solenoid. If you're in 2WD the right solenoid (pink/black) should be sucking, in 4WD the left (blue/white) should be. If these operate as described then you axle shift fork may be bad. If you're not getting vacuum when you should be, replace the solenoid.

The Vacuum shift motor ( item #10 in the diagram )

Close up :
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Vacuum shift solenoids



The other source of the vacuum leak ( if the lines to the solenoid test good ) is the vacuum box behind the battery.

P2716 Pressure Control Solenoid "D" Electrical (Shift Solenoid Valve SLT).

There are 3 things it could be.
It could be your ECM, shift solenoid valve SLT, or open or short in the circuit. I would just recommend saving the hassle and taking it to an ASE qualified mechanic.
Here is what is happening...
The linear solenoid valve (SLT) controls the transmission line pressure for smooth transmission operation based on signals from the throttle position sensor and the vehicle speed sensor.

There should be a vacuum fitting on the rear of your engine that connects to a steel line. That steel line goes down under the fire wall to the rear of the transmission to a modulator valve. If you can't find it under the hood, crawl under the truck and start tracing from there and plug it in. That should solve your problem with shifting You probably have an electric speedo and I'm lost on that.