Ok, I drive a 2001 4 door Chevy Tracker LT 2.5 V-6. I just got back from a snowmobiling trip over the weekend. Everything worked just fine, it went into and out of 4x4 every time, no problems. I get home tonight, driving into the yard to park the trailer, no 4 wheel! The light comes on and stays on, but it is not in 4x4. I looked at the hoses just to make sure one didn't come off, from what I see, everything is in it's place. It did clunk a bit going into 4 wheel the last time when I was leaving the camp, but it went in. Where should I start to look? we are expecting 20" of snow in the next few days. I would really like to have my 4x4 when it comes!

If the light is on, it means the air system is holding pressure, so I would say the problem is mechanical and in the front diff.  The air operated clutch device is failing to engage, despite the actuator holding pressure.

If the light is on, it means the air system is holding pressure, so I would say the problem is mechanical and in the front diff.  The air operated clutch device is failing to engage, despite the actuator holding pressure.

Not 100% certain on this, but, I believe a failed (open) pressure switch (in the pump module) or a bad ground to the module can bring the 4WD light on without actually engaging the free wheel clutch - the 4WD controller will see +12V on the P circuit (the pink wire at the pump) and think the system is pressurized.

When you shift in to 4HI is there a 1 second (or therabouts) delay between the shift and the light coming on?  If there isn't, disconnect the line from the pump to the differential and try again - with the line disconnected, the light should not come on and the pump should run for roughly 10 seconds.

A new pump is around $300 from a dealer or $100 from Hawk Suzuki, but yours may be repairable - depending on what's failed - I've just finished disassembling mine right down to cutting it open to get to the diapragm and valves - I took pictures so a write up is on the way.

By the way - you should be able to test this without actually starting the engine - ignition on and shifting between 2HI & 4HI would start the pump in my case (mine is a 5 speed)

Thanks for the replys guys. I just went out and checked again, there is a second or 2 delay between shifting and the light comming on. This is just happening at the wrong time for me. I spent a year out of work, now I start 12 hours days at 2pm today. Not to mention I can't get into my garage.

OK, pump is working and holding pressure. I put my vacuum/pressure gauge on and it runs to about 10lbs. I was kinda wanting it to not be working, then I could just do the manual hubs and zip-strip thing to get 4 wheel working again. Now, could it still be a blown hub? There is no grinding or anything. I can hear the pump work and it sounds like an actuator engaging, but no power to the front.

All good info!

One suggestion. Is your front drive shaft turning under power during this front "no engage" problem? Check that too, because IF you have a transfer case problem (or broken drive shaft or "U" joint for that matter), you won't get front drive even with the front diff actuator locked in and working.  

On tie zip tying the front actuator in the closed position...that will be all well and good ASSUMING that the dog clutch "teeth" of the actuator are still serviceable and not all tore up.  

The drive shaft is is good shape, no u-joint problems. I didn't check to see if the shaft is turning under power, I'll have to wait til tomorrow to check that out. I have to get off to work now. Thanks for the response. I'll take my shop manual to work and look into how hard it is to take apart and check the dog clutch. I'll only get a few hours a day to work on it, I guess I'll be driving the van for a few days.

Switch the ignition OFF and shift into 4WD, slide under, grab the front shaft and try to twist it - if 4WD is engaged in the transfer case it should not turn.

Looks like the transfer case is in working order. I just know it's not gonna be as easy as putting in a new set of hubs. And of course, blizzard warnings start in a few hours and no 4 wheel drive

Have you visually checked the rubber hoses and connections to the metal lines.  There may be a split near one of the connectors at the pump or up at the diff.  If your pump is putting the pressure out (no blinking 4WD light) you should be pulling the front end.  All of them "clunk" occasionally.  Just because the pump is putting out pressure doesn't mean the air is getting to the diff in sufficient force to push the actuator over and hold it.  The pressure could be bleeding off through a crack/leak in the line.

I did visually check the lines, they "look" ok, but that doesn't mean squat! It sounds like the actuator is engaging and staying, but that's just a sounds like. I'll get to look at it some time tomorrow I hope, I want 4x4 back!!!

I guess I'll pull the front end on it when I have time. These 12-16 hour days don't leave me much time to work on it. I'm glad I saved my old diff that just had a bad wobble in the right axle shaft. At least I'll have the chance on having the right parts to repair it. I'm not looking forward to wrenching on it out in the snow though! I need a bigger garage, or my old job back with the hoist and air tools.

Check your automatic hubs.  If one of them is not engaging no 4WD.  With the weather you are having it is probably frozen in place.  Do not pack with grease, clean and soak in ATF, that is all.  I was thinking a CV joint so I would check that next. 

Thanks BRD HNTR, good idea. Much easier than pulling the diff! I'll pull the hubs tomorrow.

I was looking in my Suzuki service manual, and I can't find any mention about the hubs. I just always like to read up before I start any type of job, I'm sure I can handle it, just wanted to read up on it first. The manual I have was a free down load from some site in the UK. Is there another section I need? And if so, where can I get it?