'99 LT 4WD Service Light
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'99 LT 4WD Service Light - 9/12/2006 10:43:10 PM
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trwolf
Posts: 22
Joined: 7/16/2006
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This is the automatic (electronic) 4WD system (4 buttons on the dash)...
Does anyone have schematics or troubleshooting guides for the 4WD Electronics (like the TCCM)??? Moreover, what feeds power to the 4WD system (fuse#’s, relays, etc)?
I have a problem with the 4WD... the TCCM doesn't click (self check) like it should at start-up. So it will not choose a mode (2WD , 4 Auto, 4Hi, or 4Lo) and all lights on the selector switch go blank. I had someone look at it (they replaced the selector switch, but it didn't help). The TCCM seems fine (visual), but I have no idea how to truly test it. After the last battery problem, the TCCM worked a few times and it was in 2WD. I got it to switch to 4 Auto, but no other modes could be selected. After choosing 4 Lo, it tried for a minute then popped the service 4WD light. That light is normally on all the time when the TCCM doesn't pass self check at start-up. The actuator motor in the Transfer case is supposed to be good according to the mechanic and it moves freely.
Any help would be appreciated. Thank you!
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RE: '99 LT 4WD Service Light - 9/13/2006 3:11:24 AM
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Chevy Lover
General Tech Moderator
Posts: 3411
Joined: 6/11/2006
From: Vancouver. B.C. Canada
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Here are a couple of wiring schematics for the switch and encoder motor.
As far as diagnostics go, it's pretty hard to figure out without a scan tool.
These pictures I'm sending , you'll probably have to put into a photo editing program so you can blow them up larger to see them properly.I can send you what I have for diagnostics, but they include the use of a scan tool.
If you click on the thumbnail and then click on the image, there is a tool to expand it a little.
Thumbnail Image
Thumbnail Image
 Attachment (2)
< Message edited by Chevy Lover -- 9/13/2006 3:16:34 AM >
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RE: '99 LT 4WD Service Light - 9/13/2006 8:56:55 AM
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trwolf
Posts: 22
Joined: 7/16/2006
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Anything you have is appreciated at this point...
It sounds to me, like the TCCM isn't getting powered correctly at start-up and the Service 4WD light stays on from initial crank. The control switch (dash) blinks all lights once for just a millisecond, but the normal self check clicking and light patterns are not there. I was wondering about some sort of ignition relay that controls power to the 4WD system, since it worked briefly after the battery change.
Thanks for the schematics... I'll look them over.
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RE: '99 LT 4WD Service Light - 9/13/2006 10:12:42 AM
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lastcoupe
Posts: 1137
Joined: 7/27/2006
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The battery voltage is supplied by the ATC fuse in the underhood fuse block via circuit #1640 which is a 3mm orange wire connected to the black 4-pin connector terminal D at the tccm.
The Ignition voltage is supplied by the 4WD fuse in the instrument panel fuse block via circuit #241 which is a 0.35mm brown wire connected to the big connector terminal #E10 at the tccm.
You realy need a scan tool to check this thing for codes though, because if there is an internal malfunction, it will set a C0550 in the tccm, and turn ON the service 4WD light.
Hope this helps, and keep us posted please.
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RE: '99 LT 4WD Service Light - 9/25/2006 8:08:35 AM
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trwolf
Posts: 22
Joined: 7/16/2006
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I'm still working on this one... The schematics have been helpful, but the details are too grainy to read. I checked on resetting the 4WD system (like what happened when I changed the battery) by pulling the two fuses RDO BATT and ATC, but I cannot duplicate the reset. I'm interested in the Body Control Module and how it impacts the 4WD system. One mechanic indicated that he didn't think the switch (dash) was getting power like it should, but the LEDs all do a quick flash (fraction of a second all at once) at crank.
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RE: '99 LT 4WD Service Light - 9/25/2006 8:13:06 AM
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trwolf
Posts: 22
Joined: 7/16/2006
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One other question... does the '99 have all the vacuum actuator equipment that so many of the other model-year's refer too. Furthermore, is there anything that controls 4WD under the batter tray in the '99 (since I had a battery leak acid all over the ground I suspect anything under the tray could be damaged).
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RE: '99 LT 4WD Service Light - 9/25/2006 10:58:15 AM
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Chevy Lover
General Tech Moderator
Posts: 3411
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From: Vancouver. B.C. Canada
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Yes there is a vacuum actuator under the battery tray.
Data Memory Retention Check
The TCCM checks the stored diagnostic trouble code memory to see if the memory has changed since the ignition switch was last positioned to OFF. This self test checks in order to see if the RAM standby power supply has been interrupted. If the TCCM detects a RAM standby power supply interruption, (the loss of stored diagnostic trouble code) the TCCM stores a DTC of 1 indicating RAM standby power failure.
This condition occurs when the TCCM is disconnected from the wiring harness or battery power is removed. The DTC of 1 automatically clears from the TCCM after cycling the ignition switch ON and OFF five times
Transfer Case Control Module Description
The TCCM performs the following functions:
- Receives input signals
- Processes the signal information
- Develops output signals
- Sends the output signal in order to control the shifting of the transfer case
The TCCM receives input signals from the following sources:
- The transfer case shift select buttons
- The NSBU switch on the vehicles with automatic transmissions
- The clutch position switch on the vehicles with manual transmissions
- The vehicle sped sensor calibrator module
- The encoder/motor range and the mode feedback signals
- The diagnostic enable
- The front axle mechanical status signal
In order to ensure the electronic shift system is operating properly, the transfer case control module (TCCM) continually performs diagnostics checks on itself and other parts of the electronic shift system when the ignition switch is in the run position. The following are different types of system checks that the TCCM continually performs.
Range Shifts
The range shifts are the shifts between the HI and the LO ranges.
- 2HI to 4LO
- 4HI to 4LO
- 4LO to 4HI
- 4LO to 2HI
A range shift can only be made with the automatic transmission in neutral or with the manual transmission clutch fully depressed. The shift occurs when the vehicle speed is below three miles per hour. Whenever a shift into 4LO is initiated, the 4LO shift select button blinks. The 4LO shift select button will continue to blink until the shift is completed mechanically or until 30 seconds elapses. The 4LO shift select button must be on and not blinking prior to shifting the transmission into gear or releasing the clutch pedal.
If a range shift is initiated when the transmission is engaged or the vehicle speed is above 3 mph, the 4LO shift select button will blink for 30 seconds and no range shift actually occurs, the TCCM will default and position the transfer case into 4HI.
_____________________________
Give a man a fish and he will eat for a day, teach a man to fish, and he will sit on a boat drinking beer for a life time
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RE: '99 LT 4WD Service Light - 10/17/2006 9:20:45 AM
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roscoe
Posts: 2
Joined: 10/17/2006
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Have you ever figured out what was the problem? My wifes blazer is doing the exact same thing. The atc fuse was blown so i replaced it. I verified that there is power to the orange wire of the black plug on the TCCM and power to the brown wire of the orange plug. The service 4wd light is also on and the lights on the switch flash for a split second. I have a OBD scanner but it does not read 4wd codes. Thanks.
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RE: '99 LT 4WD Service Light - 10/27/2006 11:24:51 AM
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trwolf
Posts: 22
Joined: 7/16/2006
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Well unfortunately, I have no answers, but I do have more information...
I cannot find any obvious cause of the problem. However, I got into my blazer yesterday after it sat in the Texas Rain (2-3 inches and the normal temperature dropped by 20 degrees) for 2 days. I started it up, drove to work, and noticed the SERVICE 4WD light was not lit and the system was in 2WD. I thought it would go back to failure after turning off the vehicle. At lunch, the normal under-dash clicks occurred at crank and it started up in 2WD again. While headed down the road I pushed in Auto 4WD and it changed to that mode. I pushed 4HI and it went into that mode. I thought surely it would fail 4Low, but in a parking lot in neutral rolling below 3 mph, it clicked into 4Low. The darn thing works in all modes (when it wants to). It came back out of 4Low at the push of a button and I cycle through the other modes one my way back to 2WD. It continued to work through 5 or 6 more stops and restarts, but this morning (the day after) it comes up with the SERVICE 4WD light again at crank. GRRRRRR!
So everything must work mechanically (transfer case and tranny). The vacuum portion, whatever it is, must work. The dash switch must work and the TCCM can work (although the problem could still be intermittent there). Anyone have any thoughts… Something that could get wet or that changes with colder temperatures? A ground problem on some portion of the system? It seems like it has be electrical/electronic since it functions in all modes (when it wants to).
As usual, any help or thoughts are appreciated.
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RE: '99 LT 4WD Service Light - 10/27/2006 9:40:43 PM
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trwolf
Posts: 22
Joined: 7/16/2006
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I think I’ve found something that affects the problem...
I have noticed that a shift from D to R seems to influence whether or not the 4WD works. More specifically, at crank the 4WD wasn’t working. I shifted into R and then turned off the vehicle. I turned the key back on and heard the 4WD system do the self-test (like it would work). I kicked it into neutral, cranked the engine, and the 4WD system came on in 2WD as normal. The next time I went to drive the vehicle (later in the day) 4WD didn’t work at crank. I put it in D, then in R, turned off key, moved to neutral, cranked the engine, and the 4WD system came on in 2WD.
I thinking either some kind of interlock switch or connector that gets squeezed or pinched with the change in tranny torque???
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RE: '99 LT 4WD Service Light - 10/27/2006 11:08:00 PM
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20Blazer00
Posts: 862
Joined: 9/16/2005
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Check the Neutral/Brake Safety switch, if you read Chevy Lovers post if that switch is malfunctioning it could affect the TCCM...reread the post...
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RE: '99 LT 4WD Service Light - 10/28/2006 1:12:11 AM
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4lowlife
Posts: 1562
Joined: 12/29/2005
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Get a new TCCM. I had to a year ago. (we have the 4 button 4wd too.)
The problems you have sound familiar.
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RE: '99 LT 4WD Service Light - 11/6/2006 10:13:37 PM
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roscoe
Posts: 2
Joined: 10/17/2006
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Well,I figured out what my problem THIS TIME was! I mean that I am quite sure that I will have more trouble with this vehicle. I wish my wife didn't like it so much.
As I stated before, the ATC fuse blew and I replaced it. The Service 4 WD light was on and no lights were lit on the dash switch. I took it to a buddy's place to connect it to a code reader. He has a Snap On MT 2500 and we tried to capture a code. There was none, but the Service 4 wd light was still on(not sure if maybe he needs some more experience using the unit). My buddy has a vehicle lift and he had an idea. It seems that he likes to tap things with a hammer, and told me to get in the truck,put it in drive and he started tapping the transfer case motor and front diff. Would you beleive that when I shut it off(while still on the lift), and then restarted the Blazer, the 2wd light came on the switch!! I put the thing in 4 wd and the 4h light came on for a second and they all went off again. We let the Blazer down and the ATC fuse was blown again. I assumed that somehow he released something in the Transfer Case Encoder Motor and took the thing home. I tried putting a new ATC fuse in but it blew instantly.I got under the truck with a meter and started testing. This is what I figured out: The Encoder motor has 2 plugs. The 4 pin plug is what controls the motor while the six pin plug is the position sensor. On the motor plug there is a thicker red and a thick black wire. When I replaced the ATC fuse the thick red wire from the wiring harness has voltage. The thick red wire going into the motor had a .8 ohm short to ground. Obviously that is what was blowing the fuse. I got a rebuilt encoder motor and tested the red wire and found that there was a 7 ohm short to ground. I assumed that replacing the motor would fix my problem and changed it. Of course the negative battery terminal had to be disconnected for quite awhile to clear the codes, but when I connected everything, it works like new.
I was pretty sure that the trouble was not the TCCM because that thing went about six months ago and I got a replacement. I could not find any after market TCCM suppliers so a new one from GM was about $965 CAD. I found one on Ebay cheap.
I would try replacing the cheaper parts first if you are still trying to fix it yourself. I have been reading alot of forums and it seems that the encoder motor is a very common problem, so I figured that I would need one sooner or later. I found a rebuilt one for $270 CAD and it only takes about an hour to change.
Good luck and sorry for the long post.
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RE: '99 LT 4WD Service Light - 1/10/2007 2:12:40 PM
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Icarus76
Posts: 45
Joined: 8/22/2006
From: Central New York
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"the Service 4WD light stays on from initial crank. The control switch (dash) blinks all lights once for just a millisecond, but the normal self check clicking and light patterns are not there."
I've been fighting this problem for about a year now with no real direction. My 4wd selector switch (on the dash) is generally unresponsive and shows no real sign of life. I have, however, seen the brief occasion for the vehicle to start with the "service 4wd" light still on the gauge panel, but with the 2wd light on the selector switch illuminated. Anything I press from there (4HI, 4LO, AUTO) causes the selected mode to blink, and blink...and then time out. Then I get nothing all over again on the selector switch.
I have an OBDII scanner, but do not have a chassis module...so I cannot read 4wd system codes. I've brought the truck to 3 shops to have codes read...and no one seems interested. Each, seperately, told me not to bother to have codes read because the GM 4wd codes are cryptic at best (ie: 4wd failed to transfer). They seem to believe that old school process of elimination is the only way.
So far, I've been through both relay and fuse boxes (under the dash and under the hood), I've been through the entire vacuum system (that I can get to) and replaced the hoses, I've replaced the selector switch, I've inspected the vacuum actuator under the battery to be sure that it is free to move and that there are no tears in the diaphram, I've been through all electrical connections (that I can get to) and inspected for wiring damage or corrosion...and nothing has made any difference at all. In all of this, all I ever found wrong was a vacuum hose showing signs of dryrot. That, along with the others, has been replaced.
At this point, and ss far as I can tell, there are 3 components targetable for blind replacement...
There is a solenoid valve at the top of the firewall on the drivers side that seems to direct vacuum to the vacuum actuator (if working properly). There is the vacuum actuator, and there is the transfer case encoder motor. I'm not sure how much the solenoid vlve costs. But, of the other 2 parts, the vacuum actuator is the cheaper. So, I'm thinking of starting there.
These sets of circumstances, described as:
"the Service 4WD light stays on from initial crank. The control switch (dash) blinks all lights once for just a millisecond, but the normal self check clicking and light patterns are not there."
seem to be uniquely seperable from many of the other symptoms of 4wd system failure. Has anyone with these exact symtoms been able to directly correlate the origin of the failure to one of the three components I mentioned (or any other)???
The closest correlation seems to come from the guy who likes to tap on stuff.
Good luck to everyone...I'll be watching.
Icarus
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RE: '99 LT 4WD Service Light - 1/11/2007 7:55:24 AM
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Icarus76
Posts: 45
Joined: 8/22/2006
From: Central New York
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OK...
I have more info. I changed my ball joints last weekend, and had an appointment with one of the chain shops for a front end alignment. I got them to read the chassis codes (for free)...and this is what I've got:
Current:
DTC 323: Transfer Case Lock Circuit Low
DTC 308: Motor A/B Circuit Low
History:
DTC 387: Unable to complete shift
DTC 2725: Active Transfer Case Mode Malfunction
Without some help, experience, or documentation, I'm not sure where the codes point me. Transfer case lock circuit low could mean that the transfer case motor isn't engaging the front transfer case linkage due to low voltage...but I don't know. Not sure what the A/B circuit is...etc.
Can someone help point me to probable origins for the DTCs, or to probable origins of the problems I'm having (supported by the DTC codes)???
Thanks in advance.
Icarus
< Message edited by Icarus76 -- 1/11/2007 1:48:31 PM >
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RE: '99 LT 4WD Service Light - 1/11/2007 9:56:41 AM
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Icarus76
Posts: 45
Joined: 8/22/2006
From: Central New York
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I think I have more info:
I also learned that the encoder motor has 4 channels. I believe the self test procedure moves through the 4 (P, A, B, and C) channels to simulate transfer through the 4 modes or ranges (auto 4wd, 2HI, 4HI, 4LO).
DTC C0308 seems to mean that the self test failed because there wasn’t sufficient voltage to move the transfer case motor from the channel A position to the channel B position (or vice versa).
Check this out:
http://www.transmissiondigest.com/tech/TD200509/200509UpToStandards/200509UpToStds.htm
I think this all points to the transfer case (encoder) motor.
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RE: '99 LT 4WD Service Light - 1/11/2007 12:33:30 PM
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swartlkk
Posts: 14528
Joined: 5/1/2005
From: Waterloo, NY
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I'll check things out more when I get home from work, but that is a great link. None of my references give the detail into the auto transfer case, but then again, I don't have my GM eSI installed anymore... LOL. I'll have to do that again sometime on my workstation downstairs.
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