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Expedition 4wd not engage

The vacuum actuator moves piston to 2wd position , but will not return to 4hd position on its own, but will with manual assistance. Does this indicate the spring is defective in the actuator?

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6ya6ya
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Posted on Jan 02, 2017

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  • 1 Answer

SOURCE: My 01 Trooper had problems

We have a 1998 Trooper that had the same problem. The fix was an electronic switch for the 4WD - a vacuum sensor - on the front axle that just plugs in. You can see it - if you look under the car from the front, it's mounted in the middle of the front axle. It cost $175 from the dealer. We had somebody install it for $50. Don't know where you live, but they are exposed and can corrode. That's what happened to ours. Good luck - hope it's the same problem. This was an easy fix, and we were pleased.

Posted on Jan 16, 2009

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wyatt1582
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SOURCE: 4 wd will not engage ,indicator lights on dash do not light

If its not engaging into 4 WD the vaccum actulator is more than likely stuck. The actulator is located on the front of the axle next to the the front gear hub it will have a plastic cover over it. Unbolt the two 10mm bolts that hold the cover on and spray down with WD-40, also pull back the rubber cover thats on the actulator staff and spray it. You might have to hit the staff a few times to get it to move just make sure its in 4WD. I had the same problem, that part is exposed to alot of water, snow, salt and so on. Or you could just replace it but its cheaper to spray it down with WD-40

Posted on Apr 18, 2009

kd6rhd56
  • 400 Answers

SOURCE: S-10 Blazer 4wd problem

www.amazon.com/Chiltons-Repair-Manual.../0801981425


Hope this helps you

Posted on Jul 12, 2009

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1 Answer

4wd light flashing


When the light flashes it's generally a sign that it's not fully engaged hi or low and or stuck partially in either position. I would say it's the force motor that physically moves the linkages in and out of position is going bad. It should be able to be scanned by a tech and give you a code.

Jun 15, 2014 | 1999 Ford Expedition

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I have a 97 blazer 4wd i repalced vaccum switch all vaccum lines and made sure actuator cable was good lights come on like im in 4wd but diff doesnt lock in and actuator not getting vaccum


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.

May 07, 2014 | 1997 Chevrolet Blazer

1 Answer

4wd front hub wont disengage


Possible the vacuum bleed-off to the switch you installed isn't allowing it to completely disengage. Pull the bleed-off line from the new switch and see if it works. could be just a tight spot/bent closed in the bleed-off line or the vent plugged.

Apr 04, 2017 | 2002 GMC Sonoma Extended Cab

1 Answer

My 98 f150 was in 4WD Hi this morning when I started it. Selector switch is in 2WD position. 4WD Hi light is on, hubs (or front differential) is engaged and transfer case engage. (Feel front wheel hop...


If the switch was in the 2WD position and the transfer case was locked in a 4WD range, my 2 SWAGs would be bad switch or the connector to the shift motor is damaged / corroded or the fuse to the transfer case shift relay module is blown ( fuse # 17 ) / problem with the transfer case shift relay module.

This is without knowing if the truck was used in 4WD the night prior, and shifted out just before turning off. If this is the case, the shift motor might be stuck, and a few hits with a dead blow hammer to the transfer case might jar it free again ( do not use a metal hammer, it could damage the transfer case ).

The vacuum shift solenoids on the firewall are controlled by the GEM ( Generic Electronic Module ) which is grounding either the 2WD or 4WD solenoid, depending on the shift plate contacts in the transfer case. ( when in 4 or 4H, the contact switch plate signals the GEM, which in turn grounds the correct solenoid ).

Pulling the switch will not cause the transfer case to go back to a default position, the switch has a resistance level for each mode, and needs that value to operate the shift motor.

The resistance values for the switch between the 2 dark blue wires:
2WD - 4100 to 3700 ohms
4H - 1050 to 1150 ohms
4L - 380 to 340 ohms
- find the wire locations on the switch, mark them and remove the connector to test the resistance.

Just my opinion on the order :

1. Check the fuses for the shift motor
2. Try the old school shift method, back up ~ 50' put into park or neutral, and shift from 4WD to 2WD.
2.1. This is to see if the transfer case shift motor is bound up, and reversing might release it
3. Try hammering the transfer case with a dead blow hammer while someone shifts from 2WD to 4WD. You only need the key in the run position, if it happens quick enough after running the engine, the vacuum reservoir will still have enough vac to operate the solenoids. Don't chance running yourself over.
3.1. If this frees up the shift motor and the vacuum has bled off, you can try starting the truck and shifting into 4H then back to 2WD to get the front axle to disconnect or manually vacuum operate the front disconnect motor by applying vacuum to the pink vacuum line on the shift motor on the front axle.

Mar 05, 2011 | 1998 Ford F150 Regular Cab

1 Answer

2003 F-150 regular cab automatic transmission and the 4WD will not engage.


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.
sscullys_111.jpg

- 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.

Jan 10, 2011 | 2003 Ford F150 Regular Cab

1 Answer

4WD does not engage.


Depending on which transfer case you have, there will either be an electronic actuator or a vacuum actuator that engages the front differential. On the backside of the transfercase there should be a round metal tag bolted to the case. It will have a number on it that starts with NP. Either an NP241, NP246, etc. This will tell you which case you have. Grab a repair manual at an autoparts shop, and it will show you the location of the actuator for the specific case you have. If you have a vacuum actuator, check the vacuum lines going to it first before replacing it. Twelve years does a number on rubber vac lines under a vehicle. You may just have a leak in one.

May 28, 2010 | 1998 GMC Jimmy

2 Answers

95 kia sportage transfer case engages, but hubs do nnot lock. my light for 4X4 lights up,


the vacuum hoses or wheel seals are leaking in the front wheels. they are vacuum operated. the dealer has kits you can buy to convert to manuel locking hubs, they had alot of problems with the vacuum hubs

Apr 02, 2010 | 1995 Kia Sportage

2 Answers

4wd does not engage when button is pressed. 4wd button flashes several times and returns back to 2wd button.


Need to have the ECM scanned. Your 4WD system is teling you there is a problem.

Mar 07, 2010 | 1999 Chevrolet Blazer

2 Answers

Front end will not lock in 4x4


if you crawl under the vehicle, trace vacuum lines to transfer case they terinate in a group of 3 (vent, vacuum from engine, line to actuator diaphram under battery) . Mark lines (bundle should have a pin to prevent bad replacement, but be safe) pop 3 hose unit , unscrew switch (count the turns to return it to same position). Transfer case side has a ball that should detent fairly easily. If stuck, work it loose or replace the switch. This manual detented switchsimply routes vacuum to diaphram which pulls cable to front axle, or vents it to atmosphere when in 2wd.

You should be able to feel if diaphram is pulling in when in 4wd and is relaxed when in 2wd mode to troubleshoot. Direct vaccum to diaphram line to test. I have used aquarium airline tubing and airstone manifold to provide quick fix when a garage and/or access to parts was not available. You want to be able to direct vent to diaphram for 2wd and engine vacuum to diaphram for 4wd.

Mar 17, 2009 | 1998 GMC Jimmy

1 Answer

My 01 Trooper had problems with the TOD starting last winter. When the switch on the dash is engaged the TOD indicator flashes continually at 4hz but the check lite does not come on. I have vacuum at the...


We have a 1998 Trooper that had the same problem. The fix was an electronic switch for the 4WD - a vacuum sensor - on the front axle that just plugs in. You can see it - if you look under the car from the front, it's mounted in the middle of the front axle. It cost $175 from the dealer. We had somebody install it for $50. Don't know where you live, but they are exposed and can corrode. That's what happened to ours. Good luck - hope it's the same problem. This was an easy fix, and we were pleased.

Jul 20, 2008 | 1998 Isuzu Trooper

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