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post #1 of (permalink) Old 02-11-2002, 01:41 PM
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4x4 Engagement problems on 99???

OK I just bought a 99 Silverado with the 5.3 engine and the AutoTrac transfer case. On the way home the Service 4x4 light came on. That kinda pissed me off, but the sale was final. (BTW during the test drive light never came one) Then I decided I better stop and recheck the 4x4 engagement and stuff like that. Well it seemed like sometimes I would have to push the button excessively hard to get it to engage, and other times just a normal push of the button would work. And also the "service 4x4" light doesn't always come on. Like today I drove 45 miles back to school and it never came on. And me and my buddies rode around all afternoon Sunday and sometimes it would come on and other times it wouldn't. So I would stop occasionally and see if the 4x4 would engage and like I said before, sometimes it would work flawlessly other times it would take several "very" hard pushes of the button to get it to light up and engage. But once it did light up it was definitely engaged. If anyone has had this problem or anything like it I would appreciate if you could steer me in the right direction.
Thanks
John

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post #2 of (permalink) Old 02-11-2002, 03:49 PM
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Re: 4x4 Engagement problems on 99???

Does it say in the owners manual what to check when the light comes on? Or does it just say...get it to a authorized service center yada yada...?

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post #3 of (permalink) Old 02-11-2002, 04:12 PM
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Re: 4x4 Engagement problems on 99???

Guys,

This is exactly the kind of post that the dozen current threads are talking about. The 4x4 actuator is a POS. There are hundreds of threads on this subject and even two in the past week.

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post #4 of (permalink) Old 02-11-2002, 04:22 PM
 
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Re: 4x4 Engagement problems on 99???

<font face="Comic Sans MS">Actually I don't think so. I believe the autotrack uses a "different" setup than that.

Plus the new ones use an electric actuator not thermal anymore. [img]/wwwthreads_images/icons/crazy.gif[/img]</font>

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post #5 of (permalink) Old 02-11-2002, 05:00 PM
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Re: 4x4 Engagement problems on 99???

Yeah, I don't think it's an actuator problem. I assumed he was saying that he is driving in 2wd, on the road, and is getting this light. That of course is not to imply that the actuator is not the problem...it may be where it is stemming from. Usually though, the actuator problem comes from the "I tried to engauge 4wd and it won't engauge". I don't have any idea why it would give him that light when he is just driving around noramlly.

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post #6 of (permalink) Old 02-11-2002, 05:23 PM
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Re: 4x4 Engagement problems on 99???

this "service 4x4" light must be on new trucks, right? i don't recall seeing one.

you drive with the autotrac on or do you leave it in 2wd?


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post #7 of (permalink) Old 02-11-2002, 05:31 PM
 
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Re: 4x4 Engagement problems on 99???

I'm not too keen on this auto track thing, but If my idea of it is right it puts the truck in 4x4 when needed even if you didn't touch the buttons - right? If that is true, then I'd guess there's something wrong with a sensor or wire that tells the auto track to come on. My idea is flawed by the possibility that these same sensors and wires are used by the ABS system too and you're not geting an ABS light. The pushing the button hard thing I think is just your imagination, I mean that it might just not be engaging and when you get frustrated and bang on the switch then it fineally does (but not due to the force used, it's because of the times tried). possibilities like relays computers and accuators may be possible. On this new of a truck I'd advise using a diagnostic tool (computer) to pull the codes after exhausting all possible "little problems". I would also talk to the dealer (if you bought it there) and give them a sob story about your new truck flashing lights at you, and while you don't expect them to fix it you would be grateful if they would run the codes so you can fix it. Save the "I'm going to tell everybody this car lot sucks ass" card for when they decline to help you. If you bought it less than a week ago and you didn't get an unbelieveable deal on it, they may fix it for you - but don't expect it. I'm sorry to hear about this, buying a new truck is supposed to be exciting and enjoyable.

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post #8 of (permalink) Old 02-11-2002, 08:53 PM
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Re: 4x4 Engagement problems on 99???

yeah it's just when I'm driving around normally or sometimes when I get down on it a bit the "service 4x4" light comes on. I always run in 2hi because right now I don't need the autotrac...so anyone have this problem?


post #9 of (permalink) Old 02-12-2002, 03:02 AM
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Re: 4x4 Engagement problems on 99???

Boss,

First of all, if your light is coming on, you definitely have something going on. These systems are not known for faulty readings. Even if you do a full check and find nothing, something usually gets worse until you can "see" it later. This is only verified by the fact you had trouble shifting the T-case. You should be able to shift on the fly between 4hi and 2hi all the way up to 55 mph. The same is true for A4WD (Autotrac). However, you have to slow down below 3 mph and put the tranny in Neutral before going to 4lo. Wait for the little light in the 4lo button to stop blinking, then put it back in gear. I assume you did this. I'm not trying to treat you like an idiot, just kinda expounding for the benefit of those other fellas who were kinda unsure about this engineering marvel known as Autotrac (don't even get me started on some of the fancy new crap I've heard GM researching for newer trucks....better get one now[sad]).

So, you have a warning that says, hey you might potentially have a problem with your 4 wheel drive. I know, that's like saying you can get kinda pregnant[img]/wwwthreads_images/icons/tongue.gif[/img]. Seriously, though, the OBD II systems on these new trucks like ours is pretty complicated these days. The Powertrain Control Module will give you that warning simply when the right parameters are met. This could mean your truck really is about to s#!t the bed, or it could mean you have a sensing problem, which is what we want (cheaper). In ALL cases, the PCM has a decent safety buffer, and gives you the warning plenty early.

Basically, if you can get access to a decent diagnostic scan tool, you'll narrow this puppy down in a hurry. The make aftermarket ones either generic or manufacturer specific. I hear either can be pretty pricey. Maybe a buddy has one? I have a list in my repair manual of the typical generic codes, and, honestly, I only see one that relates to the transfer case. Most likely need a GM specific scanner to get some good indication of what's up. Plus, the PCM in these trucks has what's called a freeze frame feature. Basically, it senses something outside parameters, lights up your little light, but then begins to record readings from any and all other sensors related to that particular system. The dealer can plug into your diagnostic port and download all that and get a chronological "picture" of what happened where...kinda like watching a little movie. Even if they make you pay for accessing the codes, hopefully it'll be one of the following things below, which you can replace on your own and be out the cost of the codes and the new part.

From what you described, it's probably one of the following things that's malfunctioning:

1) Transfer case control switch (your silly buttons)
2) transfer case shift motor
3) transfer case speed sensors
4) transfer case control module

The T-case control module is a little electronic brain of it's own. It receives the signal from your control switch telling it to engage the transfer case shift motor. The motor rotates the sector shaft where you want it (the gear you called for). It then has a motor lock on it which engages to keep it from popping out of 4wd. A transfer case encoder is a sensor also mounted to the shift motor that relays the position of the sector shaft back to the module. Once it's in the right gear, the module (transmission control module...not the same one) then sends a signal to engage the front axle. Voila...4 wheel drive. Simple isn't it?? The only difference is when you put it in Autotrac, the shift motor lock is placed in an adaptive mode by the module so it can be applied and released as the module needs it. The transfer case speed sensors can detect wheel slippage by measuring the speed of both output shafts of the T-case. They send a signal to the control module, and it commands 4hi to engage and lock. Once the speeds of both shafts become equal again (your front and rear axles are all at the same speed...no slipping), the module re-instates 2hi. And back and forth you go.

So, the light coming on could mean anything. You never said anything about grinding or leaks or jumping in and out of 4x4, so I doubt it's driveline (good news...T-cases are expensive and so are differentials). So, it's merely an engagement problem at this point. It could be as simple as your buttons themselves are bad...to a bad control module, or shift motor, or motor lock or any of those. Even though you didn't try Autotrac (or did you??), it could be those speed sensors too. It's a sensor, which means the PCM probably monitors it, which means it could have illuminated your light. The only reason that doesn't make sense is you had problems engaging in the first place, which those sensors don't handle for 4hi or 4lo.

Holy cow, that was a lot. I got carried away, but I sure hope you get it fixed man.

-Coop


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post #10 of (permalink) Old 02-12-2002, 10:13 AM
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Re: 4x4 Engagement problems on 99???

WOW! Thanks for all the info, you seem to know what the hell you are talking about, so I'll tell you exactly what happened. I bought the truck with everything working flawlessly. Then on the way home about 65 miles away from where I bought it, the "Service 4x4" light came on. I had the truck in 2hi and hadn't touched it. I was running about 70-75 when it came on. I pulled over at a gas station shut it off for about 5 minutes and took off. It didn't come back on for awhile but eventually it did. Then I got home shut if off for about 30 minutes and drove around for awhile with no light. Then I picked up one of my friends and tried to show off a bit and get on it and the tires spun a little bit, then the light came on again..and again I was in 2hi. So then I decided to try the 4x4 again. They worked fine. The next day I took my dad for a ride, no light and the 4x4 worked with just a touch of the buttons. Then later that day me and my buddies went riding around for about 4 hours and the light came on and off, and I would every so often I would check the 4x4 and sometimes it would take several pushes of the button to get anything to happen. A couple other times it worked fine. For some reason it seems to kick in to AutoTrac better than just going to 4hi. And when I would stop and put the transmission in nuetral and try 4lo sometimes it would work good other times it would take awhile. And whenever I would have trouble getting the thing to go "in" to 4x4 it would have trouble kicking back "out". I'm pretty much lost as to what I could do. I guess I'll have to get it checked with a diagnostics tester.
One more question...does the light have to be on for the diagnostics tester to get a "reading" I know on my grandma's car the light had to be on for the code reader to pick up any "bad" codes.


thanks for all the help guys.

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