[fordem]

The 98~05 Grand Vitara uses an air operated free wheel mechanism that is a part of the front differential assembly - in a nut shell - it works like this.

When you shift in to 4HI or 4LO, the stubby lever shifts the front output hub into mesh, transmitting power to the front drive shaft and also closes a switch on the transfer case, sending an electrical signal to the 4WD controller.

On early models the 4WD controller is a little black box under the driver's side dash, later models it's part of the ECM/PCM.

When the 4WD controller gets the signal from the transfer case, it sends power to the free wheel air pump (on the inside of the front bumper) which pumps air at low pressure (6~8psi) to the actuator in the front differential to engage the free wheel clutch.

The 4WD controller starts & stops the pump to maintain the required pressure and also vents the pressure to the atmosphere to disengage the free wheel clutch when you shift out of 4WD.

The pump occasionally gives trouble, the air lines will come loose or crack and leak, and it's perhaps not as reliable as it could be - replacement pumps cost a bundle, however, they're actually quite simple and can sometimes be repaired.

[fordem]

First - a quick & easy diagnosis...

If the 4WD light does not come on, or flashes when you select 4WD, there is a good chance your control system has a problem - a flashing light usually indicates a leak - so let's deal with no light first.

It may be a simple as a hose pulled off, so a quick visual check is the first step. The pump is located on the inside of the front bumper and has two rubber hoses connected to it, and leading to metal lines along the right frame rail. One line goes up alongside the radiator, this is the intake - the other goes back to the front cross-member and along it to the differential where it connects to the underside of the differential with another short piece of hose.

If every thing is in place, you'll need a 12V trouble lamp or a meter for the next step - unplug the connector to the pump and connect your trouble lamp or meter between the black & red wires, switch on the ignition and select 4HI - the lamp should come on (or the meter indicate +12V) for approximately 10 seconds.

If this happens your 4WD controller is OK - if it doesn't you need to find the 4WD switch on the transfer case and check that for continuity to ground when the shift is in 4WD.

Let's assume your trouble lamp turns on for those 10 seconds - which points to a problem either in the pump or in the differential housing.

[fordem]

Briefly - here's the 4WD controller logic.

When 4WD is selected the controller sends power to the pump module (+12V between red & black wires) - this does two things - it closes a dump valve and turns the pump motor on.

By the way - you can usually hear the pump running if you listen for it - but it only runs for a second or two if the system is working properly.

After sending power to the pump module, the controller monitors the module for feedback from the pressure switch (pink wire), the pump module will normally pressurize the system within 1~2 seconds and turn itself off, at the same time, sending a signal back to the controller, and the controller, after receiving the signal turns the 4WD light on.

If the system has a leak and never reaches the required pressure, the controller never receives the feedback and will turn the pump module off after 10 seconds as a protective measure - the 4WD lamp will not turn on.

If the system has a slow leak, the pump module may be able to reach operating pressure and turn off, but as the system loses pressure, it will cycle on and off as necessary to maintain pressure - and every time the pump turns on the 4WD light turns off - so you can actually estimate how bad the leak is from how often the light goes out.

When you shift out of 4WD, the controller turns off the power to the pump module and the dump valve opens releasing the air pressure so that the free wheel clutch disengages

[fordem]

Leak diagnosis - a low pressure guage is very helpful here.

Connect the pump to the controller and disconnect the output hose from where it connects to the differential and plug the hose (you can also do this instead of the trouble lamp in the earlier step), switch on the ignition and select 4HI - if the 4WD light comes on & stays on - the pump module and the hoses are intact - your problem is the actuator in the differential.

If you have a gauge connect it to the line rather than plugging it - you should get 6~8 psi and it should hold pressure until you de-select 4HI.

If the light does not come on or comes on & flashes (or if the gauge shows a drop in pressure), you have a leak, either in a hose or in the pump module.

Disconnect the hose where it attaches to the pump module and block the outlet on the pump (or connect the gauge) and repeat the test - this will show you if the leak is in the pump module or in the hoses.

[fordem]

Assuming that the 4WD controller is supplying power to the pump module and either the module is leaking internally or the pump is not turning on - you can simply replace the entire module ($$$$) or attempt a repair, and that's actually what this thread is about - taking the pump apart.

First take it off the bumper - two bolts hold it in place - and disconnect the hoses and the cable, next take it off it's bracket - three screws secure it to the bracket and this is what you're looking at.

Attachment:

DSCF0103S.jpg

Attachment:

DSCF0105S.jpg

[fordem]

There's a square metal cap crimped on, covering the electricals - with a flat screwdriver, gently pry the edges up and remove the cap, don't lose the sealing gasket

Attachment:

DSCF0109S.jpg

If your pump does not run - check for broken wires & bad solder joints - the pressure switch under the PCB could be defective, and there is also a splice in the harness.

You can remove the insides by taking out the two small screws and gently levering the assembly upwards - there is enough slack in the wires to get it all the way out.

Attachment:

DSCF0111S.jpg

This next picture is actually the same as the one before, but the use of flash allows you to clearly see the ports in the bottom of the module and the O ring seals - I've been told that these O rings sometimes leak.

Attachment:

DSCF0112S.jpg

[fordem]

Here's the pressure switch side - the pressure switch is a standard SPDT microswitch, clipped to a housing with a diaphragm - it might be possible to find a replacement at an electronics place if you need one.

Attachment:

DSCF0115S.jpg

And this is the dump valve - basically a solenoid with a rubber tipped plunger that seals a metal tube when energized. Look closely at the tip and you'll see a thin ring of rust - this is one of the places they leak from - you can polish the rust away with a wire brush in a rotary tool.

Attachment:

DSCF0117S.jpg

[fordem]

Hopefully you don't need to take it this far apart - to get the diaphragm out, you have to grind the top of the diaphragm housing away, and that means reassembling it with some sort of epoxy - I used Devcon plastic steel - the little red rubber piece is the outlet valve.

Attachment:

DSCF0121S.jpg

And finally the diaphragm itself disassembled - the little semicircular flap in the center is the intake valve.

Attachment:

DSCF0123S.jpg

[fordem]

My problem, which I think is fairly unusual, was that the pump would not build enough pressure to engage the free wheel clutch and trip the pressure switch - the FSM says 6~8 psi - I was getting just around 5 psi.

The pump ran fine and there were no leaks, just not enough pressure - the problem turned out to be debris in the intake valve - so basically a good clean up and new O rings for good measure and I saved myself a bundle.

I have no idea what a pump costs in Australia, but a new one in the US is around $465 - not bad for a few hours work.

[Built4thrashing]

nice write up. well done.

[MacDaddy]

Built4thrashing wrote:

nice write up. well done.

X 2
Very well done !
Some good info there !

[shabz]

Brilliant write up!

[zoukshin]

Thought I would add my own experience to this absolutely brilliant thread. I wish it existed in 2009 when I had my issue.

So, my issue was, 4WD was not engaging. I discovered that just out of the barge on Moreton island.
4WD light was coming up, but wheels were not rotating. I became rather bogged and upon returning on the mainland, I took the car to a 4wd mechanic.

'Dead pump' was the diagnosis. Second hand maybe 250$ (hard to find) new one quoted 550$. Diagnosis 65$.
I thought it was steep for a little pump (I thought it was just a pump, but thanks to this thread I have learnt it also has a pressure switch and a sensor)
Dealing with a broken diff or a mechanical issue was beyond my skills, but an electrical pump, I thought I could have a shot.

So, the 4WD light was coming up, but not engaging the diff.
I listened, and could clearly hear the pump. I removed it from the bullbar (hint, no longer in the bumper) and I could feel it vibrate, then stop (which puzzled me at first)
As any typical troubleshooting procedure goes, I checked the connections. Checked the pipes. Looked good. What the hell.
Electricals - ok
Pipes - ok
Pump - ok
Light - ok

Wait .. pipes ... I took the pipes out, checked the pump, felt air coming out ... of what I had marked 'input pipe'
Sudden realization .. could have the pipes been plugged the wrong way ? Would that explain the 4WD light coming up ??

I reassembled the whole thing with the pipes now plugged opposite to what they were. Went for a test drive, 4wd mode, light on, yep. It 4WD'd. DAMNIT, a simple pipe swap could have saved my Moreton trip. I swore, a lot.

I believe what happened was;
- People who installed the bullbar (ECB) plugged the pipes the wrong way after moving the pump.
- The 4WD mechanic I took the car to is totally useless. Won't see me again (actually I heard he passed away, RIP)

In short, if you have a problem where 4WD is not engaging despite the light on, pump working etc, simply check the pipes are plugged correctly.
I haven't had an issue since then,

[gravity_powered]

Good write up!

I had mine apart a couple of times. First with leaking o-rings and then with a bit of crap in the flap valve in the center of the piston.

On my pump the wires didn't have enough slack to get the switch and solenoid out of the body, so I had to pull the wires through the grommet a bit further. When I put it back together I tried leaving the extra wire inside the housing but it was bunching up and pushing the switch and solenoid across. This caused the new o-rings I put in to not seal properly. I had to feed the wires back through the grommet to get it everything lining up properly.


I once did a trip through Finke Gorge NP having to activate 4wd by using a bike pump on a tire valve jammed in the end of the hose to the front diff.

[Bosco15]

Awesome responses. Thank you, all.
Very helpful.
An especially big thanks to Fordem. Great write up.
I now know what and how to attack my problem.
Fingers crossed that it was just a cracked hose that prompted someone to bypass the pump.
I am pretty sure that this has been a highway car, with little if any front diff action. 360000km and the diff was mint when I had it open to retrieve spring clip.

[yeyocas]

Hi everybody,
First of all Sorry for my english and I have to say that i was looking for some place where i cuold post my greeting to the forum members but i didnt found it.

I have a question about pink wire of air pump assembly.
Somebody power with 12 volts black and pink wires. I hear a noise like pump motor is working but i'm afraid that is something wrong with that since this wires are for returning a 12 vols to controller. In the other hand. if I power with 12 v red and black wires I only hear like the motor is been locked.
Can anybody help me with this issue?
Thanks a lot.

Yeyocas

[fordem]

I would say either a loose connection on that little printed circuit board or possibly a defective pressure switch.

[yeyocas]

May be. Right now somebody has unmounted the air pump , fix something, and now, the motor is working (red and black power). But it don't stop when I block exit air hose with my finger. May be the pressure switch is not working but is there any way to fix it?

[Ricey]

Great write up fordem! Just saved me a butt load of time and money trying to figure out why my 4wd light was flashing. Got the pump apart and sure enough there was rust on the bottom of the solenoid, quick polish with some wet and dry and a new o-ring and she was as good as new. Thanks mate

[fordem]

I just had to take my pump apart - again - this time the motor wouldn't run, it appeared to be seized, and the resulting over current burned one of the copper traces on the little circuit board.

Attachment:

DSCF0121S.jpg

This picture shows the motor removed from the pump - remove the two screws and the motor can be disassembled - mine was full of water and the iron laminations of the armature had rusted, and were stuck to the magnets, a good clean up with some fine waterproof sand paper had it running again. There are two rubber O-rings that seal the motor, I coated these with a light film of silicone grease hopefully that will keep the water out.

The last part of the repair was to solder a thin copper wire over the burned trace and I have 4WD once again.

[nrtoy]

Hi Fordem,

I am currently experiencing the issues you have described in this write-up.

My issue however is that the 4WD light was blinking (due to a leak in the air hose) and that while I was in 4WD I was unable/struggled to change through my gears.

The clutch pedal was very course and when it was pressed it, it wouldn't disengage the gears.

I was wondering whether this issue is because the 4WD wasn't properly engaging and whether it affects my normal clutch.

Once I got back to main land, i changed it back to 2WD and after about 30 minutes everything seems to be working fine.

I am headed back to the beach again this weekend and the 4WD light seems to stay on constantly, but I am unsure whether the issue I was experiencing is directly attributed to the 4WD mode not properly engaging.

Thanks

[fordem]

I've read your thread on the Suzuki forum, and you appear to have multiple issues - your clutch disengagement issue is in no way related to this.

[robnkylier]

hi guys,
this is the exact article i am after, but the pictures do not load.
the word "image" is there, but no photo, and clicking on them does not open up an image either..

turn ignition to "on", 4wd light comes on in the dash, and you can feel the pump click for an instant, but no air coming out of either pipe and the pump doesn't vibrate at all.
so looks like i need to pull the pump apart, so the photos would be really handy.

thanks in advance.

[Beniblack]

Great write up it explains a lot.. I currently have a 2002 GV with output bearing problem.. I am swapping diff for one I have out of a donor 2000 GV I know has done very little off reading as previous owner never used 4wd. Only off reading it's done is by me on the beach for about 4 years. So should be in good condition.. Now after reading this thread I realise I had the intermittent 4wd light problem when it was in other car and just assumed it was a stuffed dash light. I have the diff out of car now so can't test as mentioned. So I wish to test donor diff actuator before swapping to other car. How would I go about this? Could I possibly just run air hose from pump in new GV and hook up to donor diff on the ground and hope the 4wd light comes on? It does stay on currently with buggered bearing diff that's in the car.. I've fitted locking hubs atm and unlocked until I get time to do the swap..

[fordem]

The easiest way to test the diff actuator is going to be to hook the pump to it. My preference is to use a hand pump, which not every one will have access to.

[Beniblack]

Ok will go get a decent length of pipe & try that. So if I'm reading correctly the pump will sense when the pressure is up & the 4wd light stays on? So just need to hook the pump hose up then not the vent from top of diff..

[fordem]

That is correct - just hook up the line at the bottom of the diff to the pump outlet and if the actuator is holding pressure the 4WD light will turn on & stay on. By the way, you don't need to run the engine for this, just switch the ignition on.

[Beniblack]

Worked a treat.. Solid light so I'm good to I reckon.. Thanks..

[ml30kl]

Hi I Mikey from Macedonia and i have the GV 03 petrol 2.0 and after i change the clutch plate i have the problem with 4wd.
No indicator light
Not engage 4WD
All pipes and connectors is ok
Not work actuator pump
4wd switch on top on the transmision have the power In wires.
I noticet input wires on actuator have 5v power must be 12v or more?
Eny solution?
Sorry for my bad Engl.

[fordem]

First - if the problem showed up after clutch replacement, go back and recheck what was done/disconnected during the clutch replacement - presumably the transmission/transfer case was removed to replace the clutch - recheck the switch connections, make sure the 4WD switch is connected correctly, there should be no "power in the wires", the switch grounds a connection to tell the ECU/4WD controller that 4WD has been selected - the wire color here is black/orange and a black ground wire.

The pump connector should have three wires is it red, black & pink - using the black as reference, you should see 12V on the red wire, but it will only be there for 10 seconds after 4WD is selected if the pump is not connected or working properly.