GMC Jimmy 4WD Problems

rcf

I have a 2000 GMC Jimmy SLT that I purchased knowing the 4WD didn't work. Afetr the sale I put it in a small,private shop and they said (if I understood correctly) that an ABS sensor was out of alignment and something about a bearing was not allowing it to go into 4WD. They fixed it and after I left I tried it out. It now goes into four wheel drive but the following occurs.
1.If you press 4 Hi from 2 Hi.....the 2 Hi light goes out and 4 Hi light blinks but does not stop blinking although 4WD is engaged(I can feel it while turning).
2.When selecting the Auto 4WD button the Auto light starts blinking and instead of being in the 4WD "on demand" mode it goes directly into 4WD.
3.No code or check 4WD lights appear on the dash.
The repair facility had closed for the day when I discovered all of this and I plan on going back but I just wanted some ideas as to the problem before I do. Thanks for any help.

repairdog

Heres the story:
The front hubs each have an ABS sensor in the 1 piece hub for the ABS and Autotrac (only 4wd mode effected) to work. The rear sensor is in the transfer case.
The passenger side front axle has a coupler that engages the axle to the front differential when any 4wd mode is activated and a sensor tells the TCCM computer in the cab located in the pass side kick panel its engaged. That axle has a vac actuator under the battery that is vac activated and it pulls a cable from it to the axle. 99up have an additional electric switch for the vac mounted on the firewall. CHECK all vac hoses from the intake to reservior (in drivers front fender) to the firewall switch, to the actuator under the battery (5/32 small and 7/32 larger). Note that both front axles CVs always turn as well as front drive shaft. Thats covers Autotrac and 4Hi. For 4Lo the transfer case has an encoder motor that is on the transfer case that engages a lower gear when you stop, put trans in neutral and push 4 lo and a clunk is heard. Again a sensor on the transfer case to tell TCCM it is engaged. Hope that wasn't too confusing. Blinking dash light means the sensor did not work/actuator did not work/ or the TCCM computer is confused - yes it can happen. After you check all operations try and disconnect the battery for 30 min and then retry and that should have cleared any error. Finally, check the front diff fluid and make sure its full and the transfer case requires blue autotrak II GM fluid - this has a GM bulletin on it so do not use Dexron red in it due to the clutch packs in yours.

reddog719

my 98 jimmys lights flash when you try to put it in 4wd but doesent engage. the only way I can get it to engage is to put it in neutral hit the low lock button and while its flashing put it back in gear. but it will only go into low any suggestions?

repairdog

Many posts on this if you search the main area.
Assume 3 button 4wd (no Autotrac):
1. Check the vac hoses from the untake over to the reservior and T off to the actuator under the battery tray.
2. Chack the actuator (crawl under the pass side front) by looking /listening to see it the cable pulls the axle coupler.
3. Check the front axle coupler sensor(wires to it) by unscrewing and pushing the ball in) which tells the TCCM or 4wd computer that the axle is coupled for all 4wd modes.
4. Check the similar sensor on the transfer case for the encoder motor that engages the low gear for 4LO.
5. Check all connectors are tight and wires not cut all the way to the transfer case.
6. Disconnect the battery for 30 min and see if the TCCM reboots (must be a windows system - thats a joke) cause often this does fix it as it hangs up.

larenz71

I bought a 1986 blazer and having vibrations and leaks fluid.I changed transmission fluid I am thinking it may be transfer case. I have enabled 4xhigh and have been driving around for a short period time. Is this a good idea to loosen up gears,etc.? This is my first 4x vehicle.

repairdog

No, 4hi is only to be used off road where the wheels can slip and not bind up the drive train. Snow is OK too. Its 20 years old so will leak at the seals. Change the transfer case fluid too. The drive shafts exit from the transfer case and there are seals there that can be replaced easily. Check/change the front and rear differential gear oil and the pinion seals can leak there too. Vibration must be traced to type - tire or drive train. If the U-joints are original and have no zerks on them they may be loose. Check the front wheel bearing and tire balance.

lskarvan

I can't get my Jimmy to go into 4X4, did anyone else have any problems with this? Please help me out.

repairdog

Do a search in the forum on this and many answers already posted on the components to check. I'll give you more after you do that.

jenfen2

I have tried a new motor , light just flashes and won't go into 4 high or low. I also had a brain box from a junk yard and 2 wheel drive just flashes and won't go into 4 high or low. I can take motor off and put in 4 wheel drive by hand, so I know the acuator works.

lskarvan

Thanks, I will do a search now. I am new to this so I really don't know where to go for my answers.

rick1002

I have a 2000 Jimmy SLT and 91,000 miles when I started hearing a thumping noise underneath when I would start to drive or slow down and stop. My mechanic says it is the transmission, that a gear is getting worn down and will eventually break and I will lose Reverse, 2nd and 4th gear. Is there any truth to this and is there a quick easy fix? I thought maybe it was just the U joints, but he says no that I will need a transmission overhaul and that is a common occurance with certain transmissions.

repairdog

Sorry I don't always see the Jimmy stuff.
That rev/2/4 thing is caused by an internal broken Sunshell and the neck breaks off all at once usually from drivetrain shock as hard 4wd or towing. Noise could be many things as u-joints, hubs, brakes, tires etc so need to look under it and start checking. Also look at the transfer case fluid and change every 50k as well as trans fluid/filter.

bangorbear

On my 2000 Jimmy, when I press the 4WD button, I hear the clicking and I feel it shift. REALLY feel it shift! Feels like I've got the brakes on. Vehicle starts to slow down slightly and there is a low whine. When I press the 2WD button. There is a loud Bang :surprise: or thump and it goes back to 2WD. My daughter recently had a ball joint replaced by a shade tree mechanic. I switched vehicles with my daughter so not sure how it has been cared for. She did take it to the dealer last year due to a loud...REALLY loud siren like whine from the 4WD. That cost $800+. Winter is coming so would like to get the 4WD working correctly. Thanks all for your help.

repairdog

Assume you are pressing 4Hi and you get the bang.
Front drive shaft always turns and keeps both diffs at same speed, so when you depress the 4Hi vac makes the actuator under the battery tray pull a cable that couples the pass side CV axle to the diff (drives side always connected). If thats the bang then see if the actuator vac line is good and the actuator pulling the cable. The 4Lo will only work at a stop in neutral or a 3mph or less roll in neutral, then the lower gear in the transfer case engages. That really loud noise FIX needs to be looked at to see what they really did - if the 4Lo gear is being engaged when 4Hi is pressed you have a sensor problem - probably best to go back to the last work shop and ask or pay the dealer to determine - this gets very expense very fast. If you have 4 button Autotrac the transfer cases sometimes have clutch problems and use special blue syn fluid to smooth out.

bangorbear

The Bang comes going back to 2WD. When going into 4WD, you hear the clicking of the relays and feel it shift and hear a low whine/rumble. 4LO seems to be working as advertised. I brought the car to a stop and engaged 4LO and then 4Hi and there is an obvious difference so it is going into 4WD.

repairdog

I am somewhat confused - so you have regular 3 button 4wd and are engaging it on the hard street and driving it, then say it bangs going out of 4wd - it should cause you are probably binding up the drivetrain so do it on a soft surface like dirt and report back. These 3 button systems are NOT designed for street use at all - snowing or dirt allows slippage between front and rear diffs. 4Lo engages the transfer case low gear and you hear a clunk as it engages and disengages.

bangorbear

Yes, it is a 3 button 4WD. Today I took it out in a dirt parking lot and along a dirt road and it still does it. Goes into 4wd with a low whine and goes out with a bang. On the hard surface, was at low speed and going straight.

repairdog

If you mean 4Lo then the encoder or shift motor on the transfer case is binding up when its disengaging the low gear so first see if any fluid in the transfer case - make sure its full and I'd change it.
If its 4Hi then have to look at the front actuator under battrey going to the pass side axle.

bangorbear

What should I be looking for? This is my first 4WD vehicle.

repairdog

They all clunk loudly when the 4Lo is disengaged and engaged so maybe try doing it at a 2-3 mph very slow roll - thats the best way so the gears can unmesh easier - I do that and it aviods much of the noise. This is for 4LO only of course as the 4Hi can be done up to like 55 mph (stated in your owners manual). Maybe that will help or when you see another Blazer ask them to engage and disengage to compare - many will be glad to help you as they have had similar things hard to explian without comparing. I have 3 4wds so often see if the others do the same thing - ops, guess thats really not a problem but a Blazer design quirk.

jenfen2

I have tried a new motor , light just flashes and won't go into 4 high or low. I also had a brain box from a junk yard and 2 wheel drive just flashes and won't go into 4 high or low. I can take motor off and put in 4 wheel drive by hand, so I know the acuator works.

repairdog

The encoder motor is ONLY for 4LO and there is a sensor to tell the TCCM that its engaged or not and both 4LO and 4HI need the front axle coupler engaged and the sensor on the axle to read it is or light will flash. Work on 4HI first and get that to work then worry about 4LO and encoder motor.

jenfen2

Where is the sensor located at on the front axle? Or is it the encoder motor?
Because if I get under the jimmy I can put it in 4 wheel drive by hand, it's just when you try to put in 4 wheel drive with the push button it will not go.

repairdog

To do searches on past posts enter the query in the "search" field when you are at the main page so it looks in all Blazer/Jimmy sections.
Front sensor is on the pass side so look under the vehicle and see the electrical connector plugged into the soild outboard part of the front diff. Encoder motor is in the transfer case for 4Lo only and a sensor on top of the transfer for that too (hard to see). The TCCM or 4wd computer in the pass side compartment kick panel controls all operations. I must assume you are only engaging the encoder motor for 4LO by hand and if the front axle is not engaged and sensor tells TCCM then the light blinks and no go. #1 check all vac lines from the engine down to actuator first.

doyarace

My 2000 Jimmy wouldn't shift out of 2x... Tracked the vacuum line from tranny to somewhere under battery. It came out through plastic harness to the firewall. About dead center just below the hood gasket theres a black vacuum actuated switch. It is either the switch (i doubt it) or the vacuum line is dry and crcked. Look right where the line slips on the nipple. It gets VERY hot in the engine compartment and alot of problems are from cracking vacuum lines...

guest

Vac line runs from the intake by the PCV hose, over to the drivers side fender/firewall where it Ts to the vac reservior can in the fender and to the 4wd and heater(hard plastic one). Then to that switch on the firewall so check all lines and replace 5/32 (and 7/32 for larger line) vac line. See if when in 2wd there is vac to the inlet side and none out the oulet. Then select 4Hi and see if vac on outlet - if not its probably the switch. The vac then goes down to the actuator under the battery tray that has a diaphram and it pulls a cable to the axle coupler. If that doesn't engage no 4wd. A sensor on the axle to tell the TCCM or computer that its enagaed or not. $lo needs that first also then the encoder motor puts in or engages the Lo gear in the transfer case. Once all is fixed and it still won't work pull teh 4wd fuse or battery cable for 30 min to do a TCCM reset (sometimes the logic gets confused).

lanae2

I have a 1995 gmc jimmy 4wd ,,,Does any-one know how to R&R my front passanger hub.....

repairdog

Buy the bearings and seals and a 36mm hub socket and go for it.

jackassjay

I have a 99' Chev Blazer and went to use the 4x4, but to no avail. I can press the button on the fly and in park and in neutral and nothing. All it does is flash the 4hi button and goes back to 2hi. I can hear it trying to engage at the transfer case but it sound like the encoder motor is seized or dying. It does this as well when I try 4lo. I'm at the end of my rope this ride as it only has 120,000 km. I've replaced so much it's rediculous. I need to fix to sell....Thanks Jay

mcleod9

I bought a 1996 Jimmy knowing it was a two wheel drive truck just because I was desparate for a car. But now I was gonna start working on it and fixing it up. I would love for it to be a 4x4 but I have no clue as to how hard this would be or what I would have to do or what I would need to do this. If anyone has ANY help it would be greatly appreciated. Thanks! :confuse:

repairdog

Push the 4Hi button and see/listen if the front axle coupler engages - thats all that should happen. If not follow the vac lines under hood and to the firewall center where a solenoid is mounted - is vac to it and when you push the button does it open and allow vac thru?
Transfer encoder motor is only for 4Lo.

repairdog

No way - buy a 4wd. The transmission rear is diff, need a tranfer case. front diff, and finally the whole front suspension is diff so its nearly impossible and would be a headache and $$$$.

preacher4jsus

4-wheel drive not working. Replaced switch,but will not engage into either 4-hi or 4-low. Anyone have any input as to what the problem could be?

jackassjay

I have vacuum to the actuator under the battery box. Today I replaced the vacuum actuator and nothing replaced the switch on front diff, switch on t-case, encoder motor traced the vac lines checked fuses again. Is the selonid on the firewall down behind the distributor? What about the modual?
Thanks Jay :sick:

repairdog

The solenoid is mounted on the firewall right under the hood seal - trace the vac line it goes thru it. If you push 4Hi with the engine running you should hear the vac actuator engage the axle coupler on front diff. If that occurs and the the new sensor switch you installed should tell the TCCM (computer behind the pass side in cab kick panel) that all is right engage 4HI and set the dash light to 4Hi. If you do not hear the actuator then it or the solenoid are bad. If they work then pull the battery cable for 30 min and reboot the TCCM and all may work fine - they get confused and hang sometimes, really just a cheap processor.

jackassjay

I can't seem to here it engaging at front diff... I can see the cable move from the actuator when I tested the vaccum actuator... What must I do now?
Thanks Jay :confuse:

repairdog

Buy a plastic in line connector and bypass the firewall solenoid (connect vac lines together) while running and see if it then engages. Solenoid is GM only at $45 and they do fail and leak internally - just changed my 99 but may be the sensor on the front diff also not seeing the coupler move - its a little ball that gets pushed up as the axle couples and sends the info to the TCCM then the dash light goes solid on for 4Hi. That sensor just unscrews off the axle so you can check it and the electrical connector.

mudman1

I have a 97 Jimmy that I put into 4wd (hi) and when i try to switch back to 2wd all I hear is a couple small knocks on the transfer case. The 2wd button flashes but it will not switch back to 2wd. I have tried moving forward ,backward,park neutral,accelerating,coasting. Nothing seems to work.
I need to get this problem resolved as I drive a long distance to work every day. Any suggestions?? TIA

repairdog

Check the vac lines under hood and then the one down to the transfer case (its 5/32 and is T off at the drivers side under hood and goes back behind the engine and down. 98 and earilier have a NP233 transfer case with a 3 port vac switch mounted on it that engages the front axle coupler and the front driveshaft. Look up under the Blazer on the drivers side at the transfer case just behind where the front driveshaft comes out. You can get a replacement Motormite #49315 for $15 at Advance and its on the Help part isle. Use a 7/8 box end wrench to remove after simply pulling the formed rubber top connector off. The formed rubber fitting is keyed to the tab on the switch top so hard to get wrong. The switches leak around where the pastic top meets the metal bottom usually. If the plastic top can rotate it leaks for sure.

mudman1

I checked all the vac lines and they all seem to be in good shape. I noticed than the actuator, under the battery case, does have vacuum to it. When I pull the line off the actuator, the cable running down to the front diff moves and the front axles are no longer engaged. Although the 4wd light does not go out. I also noticed that some front diff fluid leaking out of the diff. Further inspection found a loose front plug left that way from the oil change place. I still have plenty of fluid so I'm hoping nothing is damaged or seized. I assume that the switch on the axle housing is the one that turns the 4wd light on and off. Is it common for then to stick leaving the light on?? I'm not really sure how this system works as far as what happens when it goes from 2wd to 4wd and back. Could I do damage to the transfer case driving with the front actuator disconnected until I have more time to get more info as to where to look next?? Thanks Rob

mudman1

After a double check on all hoses I was still unable to find the problem with my issue (not coming out of 4wd). I'm very curious as to what I am hearing in the transfer case below the vacuum switch. It is 2 sets of small knocks. Only when I push the 2wd button. I hear nothing when I push the 4wd button so I'm assuming that the transfer case may still be in 4wd. The 2wd light still flashes a couple times while the knocks are heard. I also hear relays or something under the dash. Is there somewhere I can find out what happens when one of the buttons are pressed?? (Relays,vacuum solenoids if any.)I use to be an ASE cert. Mechanic many years ago, before I started having problems with my wrists hands and elbows do to many years of air tool use.

repairdog

Under the hood on the drivers side find the vac lines and at the last T you will see 1 line that turns to plastic for the heater and the other runs to the transfer case 3 port switch (line runs up over the PB assembly and down the rear of the engine pass side then crosses over to the transfer) - pull that one off and cap the T off and that will disengage 4wd and allow you to drive till you fix it. Most likely is the 3 port switch for $15 but hard to reach so if bad wrists go to a trans shop and a quick change and you will even stay clean!

mudman1

I removed the line at the actuator. I just wanted to be sure there was nothing in the transfer case that also had to move (electronically}like another gear or fork to disengage anything in the transfer case. I will be replacing that switch today. I'll let you know how it turns out. Still not sure what turns the 4WD lights on and off. Thanks, Rob

mudman1

I installed a new vacuum switch this morning and found it was stuck in the pushed in position. I checked the hole (with mirror and light) that it screws into and found that the lever that pushes the button up was covering the hole. I'm assuming that something has moved in the transfer case to cause this to happen. I checked the transfer case fluid and found it was about an inch or so low. I am hoping that nothing has seized in the transfer case. I have been told that I should have a synthetic fluid in the case but it looks and smells like burned ATF. Anyone know what is really suppose to be in there? obviously NOT burned anything

guest

1.1 qts of Mercon-Dexron II red fluid. There is an electric shift motor that moves that lever controlled by the dash switch and the lights are set by the TCCM located behind the middle of your dash (pretty sure on that year - they moved them several times).

mudman1

After hours of changing fluids and checking switches I was finally able to coax it back into 2wd. After talking to a very good GM "Heavy Repair" mechanic I was not able to get in touch with for the past few days, He told me that sometimes the TCCM that is located in the passenger side kick panel sometimes gets moisture in the connector. He said Disconnect it and Spray the connector ONLY with WD40 and blow it dry with compessed air should take care of this problem. He has seen a lot of this happen. He has also replaced quite a few Encoder motors on the transfer case. I sprayed the connector on both the TCCM and encoder motor and blew them dry as instructed. I also gave the encoder motor a couple wacks with a small PLASTIC mallet hoping I would shake something loose or back where it belongs. I pulled the fuse before I started the other things and after I was done,I replaced the fuse and pressed the 2wd button and was very happy to see that something worked. I cant be sure what actually worked I'm just glad its out of 4wd for now. (Till the snow starts flyin'.) I will have to truly diagnose the problem when I have more time. Thanks for the replies it did help narrow the problem.

j2ther

I have been messing with my car to get it into 4wd. it will not engage, in the past the 4hi light has blinked and i would have to unplug the battery for a minute and plug back in and then the 4wd would work for about 3-5 switches from 2hi to 4hi. but lately, the past 24 hours of trying to switch into 4hi and even 4lo the lights will engage but the 4wd itself will not be engaged. i have tried pulling the 4wd fuse out, as well as the trans fuse. neither have done anything. right now i have my battery unplugged and will leave it for a half hour to see if that will help reset the transfer case. when i try to engage 4lo, it will engage but the 4wd wont, i can hear the transfer case parts moving and the transmission goes into the lo range gear but no 4wd just 2wd. from what i have been reading it sounds like the vacuum switch on the transfer case, its 10 degrees here and snowy so i haven't felt like getting under my car to check the lines yet. another possibility i have been reading about is the selnoid on the firewall. anybody have ideas as to what is causing this and a fix for me?

repairdog

You should have a 233 transfer case, 3 button so this is based on that. There is a vac line that runs down to the drivers side of the transfer case to a vac switch that controls the front axle actuator. Its a $15 part that I would say is the most common problem with all 92up 233 cases. Its a 3 port vac switch Motormite/Dorman #49315 and I just did a 98 same thing. Need a 7/8" box end wrench to replace and the formed rubber connector is keyed so pull it off. Hope that does it.

97jimmyslt

It "sounds" like i have an electrical problem!
The internal warning speaker (not sure of it's technical name somewhere inside the dash) is ALWAYS on as long as the key is in the ignition. It started last week, coming on periodically and now it progressed to non stop being all the time. i checked all fuses and they are ok, and i have no error codes displayed on my dash. Any ideas or advice? Were exactly is the speaker so i can remove it?

Tony

repairdog

Do you mean the key in ignition buzzer noise - if so only the 97 (your lucky day) has a known ignition problem with the ignition module (wires and connector in the steering column) but called the ign switch. Change it out and good to go.

rrrccc01

Greetings,

I am about to replace all the 4x4 vacuum hoses just to make sure they are right. I have read that they are 5/32" and 7/32". Some questions...

1. Tis is ID, correct?

2. Silicone hoses are OK?

3. Most hoses I find are metric, that is 4mm, 6mm... research is not clear but I believe I can use 4mm and 6mm, correct?

4. Approximately how much, in feet and meters, of each do I need to replace all the 4x4 related hoses?

Regards

RC