Mechanics

CHEVY 4X4 ENGAGING

1996 Chevrolet Truck

1996 Chevy Truck V8 Four Wheel Drive Automatic 180000 miles

I have a 1996 chevy 4x4 Z71 5.7. I put it in 4wd last week while I was on a wet slick dirt road at the hunting club. When I got on the paved road I took it out of 4wd. A a few mins. Later I tried to put it back in 4wd and it would not engage. I have 3 buttons on the dash one is 2wd one is 4wdh and one is 4wdl. The light on the 4 high and 4 low would just flash. I can hear the transfer case shifting into 4wd but the front dif is not activating. To make it short the light on the buttons will flash but the front end will not lock in to 4wd. Nothing I that I do will make the 4wd lock-in. I disconnected the plugs from the Actuator Switch one of them had a little water in it but it looked like new inside. I checked the voltage on the plugs with my fluke meter. I was getting around 6 volts on one and around 8volts on the other one. I am guessing the actuator is a normally closed contact because with the I actvated the 4wd there was no reading(voltage). I also checked the fuse and it was good.
What is keeping my 4wd from activating?
Avatar
1996z71
October 7, 2010.




To help me better visulize your condition, I am going to start basic. When you are in 2wd sitting at a stop, in park or neutral, and you press four high, do you hear anything, and does the light continuously flash or revert back to 2wd. How about four lo, you should definately hear and feel that shift, as well as the gear reduction, does it continue to flash, or revert back to 2wd.
Which wires(what colors) at what switch did you check? At the actuator I am showing a two wire connector, a light blue wire and a black wire. The black wire is shown as hard wired to ground(g105). There is also a front axle switch that has a two wire connector, the same lght blue circuit as the actuator, and a black white hat looks like, in theory, should be grounded by the transfer case control module. There is a bulletin, and a revised schematic, if the new styl front axle actuator has been installed.

Factoryjack
Oct 9, 2010.
When I press the 4wdh or 4wdL I can hear and feel the transfer shift. The light on the 4H or the 4L will flash on the button that is pressed. It does not revert back to 2wd until the 2wd botton is pressed I let it flash for about 10min the night it started doing this. I can hear the switchs or relays in the dash when the 4wd bottons are pressed but I havn't went into the dash and checked them. The wires that I was talking about are the wire that go to the actuator under the front end (not sure what the proper name for it is but it is where the actuator for the 4wd is located or the gear box that locks the front two cv's in to make it 4wd.) One set of wires went directly to the actuator switch and one set go above it on top of this front transfer case(gear box).
Sorry I can't discribe it better. I am a electrical eng. And I don't know certain terms of car parts. It seems to me that everything is working but the final part that makes the 4wd lock-in. So what do you think. If this doesn't help then I will get my brother to discribe it better tomorrow he knows what all of name of these parts are.

Tiny
1996z71
Oct 10, 2010.
If you check the two wire connector at the front axle actuator, one should have 12 volts when 4wd is selected(light blue). The other black wire should have continuity to ground. You could also connect a test light across this connector, and when 4wd is selected, the light should light, does it?

Factoryjack
Oct 11, 2010.
Ok, I put the truck in the guarge where I could get some light on the situtation. I unpluged the connectors at the actuator I am getting around 13vdc when I press the 4wdh or 4wdl buttons. I might be wrong but it sounds like the actuator is not activating. A couple of questions. If it is the actuator and I take it out will the gear oil drain out when it is removed if so where and how much oil do I replace it with. Also what is the other two wires for that go to the transfer above the actuator.

Tiny
1996z71
Oct 12, 2010.
Was that 13v using the ground at the connector for the actuator? If you remove the actuator, you should not have much oil leak out, maybe even less to none if you lift the RH front side of the vehicle a bit. If you do have some loss, the fill plug is on the LH side of the differential, above the drain plug toward the front. The fill plug is 15mm, the drain is 13mm. Fill it through the fill hole until fluid runs out.
The wire colors at the actuator should be light blue, and black, is that correct? What are the wire colors that go o the other item that you are speaking of. My guess is, it is a switch that will confirm that the actuator is locked in, this may be what will stop your lights from flashing. The problem with the service information that I am referencing, is it gives no component location description or views. I am going off of the wiring schematic from ALLDATA.

Factoryjack
Oct 13, 2010.
Yes, I plugged the leads of my fluke meter in to the connector for the actuator and this is where I got the 13v from. I am getting power to the actuator but it is not engaging. The wires both look black or dark blue to me I could not tell, But there is not a light blue wire. If the actuator is not working then it is not going to activate the switch at the actuator to sent a signal back to the switch in the dash to let it know that the 4wd has been actatived. I am thinking that the switch above the actuator is working like a limit or some call it a lever switch. Once the actuator is engaged it actavates the switch above the it and it will send a signal back to the dash switch to let it know the the 4wd is actavited.

Tiny
1996z71
Oct 14, 2010.
That switch actually sends the message to the transfer case control module. A quick test would be to jumper the terminals of that switch together. If this stops the lights from flashing, and you are getting the signal to the actuator, then I would suggest a bad actuator. You might be able to bench test the actuator by applying power and ground to it. The symbol in the actuator shows that it is a coil of wire, or a resistor of some sort. You could also check the continuity of the actuator. If it is open, then it is safe to say it's faulty. Service information does not specify an electrical specification for the actuator. It should have some resistance, probably like a fuel injector or similar, possibly 10 to 20 ohms I would guess. Substantially low resistance could indicate shorted windings, excessively high could indicate high resistance or open circuit. I believe the case of the actuator is plastic, so if it was shorted to the case it would not find a path to ground. The following bulletin may interest you if you need to replace the actuator. I am not certain if this upgraded part and procedure address just the complaint as stated, or if it is necessary in the case of any actuator replacement.
Drivetrain - Slow Or No Engagement of Front Axle

File In Section: 4 Drive Axle

Bulletin No: 76-43-01A

Date: September, 1998

Subject: Slow or no Engagement of Front Axle when 4WD is selected (Replace Front Axle Actuator)

Models: 1988-97 Chevrolet and GMC K Models
excluding 1988-93 Models over 8500 # GVW

This bulletin is being revised to add information to the Service Procedure, add a new part number, and include schematics. Please discard Corporate Bulletin Number 76-43-01 (Section 4 - Drive Axle).

Condition

Some owners may comment that the colder the outside temperature is, the longer it takes for the front axle to engage when 4 wheel drive is selected, or the front axle does not engage.

Cause

The front axle engagement actuator is a thermally activated component. Because of this characteristic, the time required for the actuator to complete 4 wheel drive engagement is extended as the temperature drops.

Correction

Replace the front axle actuator and include the applicable wiring harness kit. Refer to the Parts Information in order to determine which wiring harness kit is needed.

1996 model trucks with a build date on or after January 2, 1996 are considered as " 961". If the build date of the truck is unknown, verify the 3 character " axle code" on the front axle label in order to determine which wire harness to order.

This new actuator uses a motor to engage the front axle and is not affected by temperature. On 1988-93 models with a GVW rating over 8500$, the new actuator cannot be installed and the thermal actuator will remain the service part.

Parts Information

P/N Description Qty

26060073 Actuator Asm, Frt Drive Axle 1
22510339 Fastener 1
15313272 Harness, Jumper (Z Splice) 1
(86-93 K1-3)

Parts are currently available from GMSPO.

Warranty Information

Some owners with actuators that are operating as designed (5-30 seconds engagement time) may choose to upgrade to the fast actuator at their own expense. The fast actuator is a new product enhancement and should not be used to replace actuators that are operating as designed.

For vehicles repaired under warranty, use:
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Factoryjack
Oct 14, 2010.
Ok i'm back. I changed the actuator tonight the 4wd works know. But the lights are still flashing on the 4wdh and 4wdl buttons. I also tested the old actuator. It was dead I could not get it to do anything. What do you think is going on with the flashing switchs. I even disconnected the battery to see if this might reset something. Do you think that it could also be the other switch on the hoghead. I will try to jump the switch's wire togeather tomorrow night and see if the lights quits flashing. If you go to O'ReillyAutoParts. Com and type in the part # FWD18. This is the switch you are talking about. BWD - Four Wheel Drive Indicator Lamp Switch
Part Number: FWD18

Tiny
1996z71
Oct 25, 2010.
I am wondering if that is not indicating there is a system fault. Explain the flashing in detail, and I will provide you with the info that I have. When you are just turning the truck on, in 2WD, the indicator is?, on solid?. Say you make your first request to 4HI, does all the indicators flash, or just 4HI? Does it continue, or revert back to 2WD? What about 4LO? It is capable of displaying trouble codes through that switch(indicators), it requires jumping a terminal at the DLC connector, are you familiar with that connector?


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Fig. 25 Data Link Connector Pin Terminals

Displaying Diagnostic Trouble Codes

Install jumper wire between DLC terminal 13 and ground, Fig. 25 . The DLC is located under the lefthand side of the instrument panel, right of the steering column.
Turn ignition switch to On position.
Wait three seconds, then observe transfer case switch status lamps.
Reading Diagnostic Trouble Codes
The transfer case status lamps will flash to indicate the DTC's stored in memory. If only one DTC is stored in memory, that DTC flashes repeatedly with a three second delay between flash sequences. If more than one DTC is stored in memory, the first DTC flashes once, then the next code is flashed. This sequence continues to flash until the jumper wire is disconnected.

Fig. 28 Test A: Status Lamps Flash


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You said you disconnected the battery, and one would think that would clear a fault, but here is the code clearing procedure.
Clearing Diagnostic Trouble Codes - NV 243 (Electric Shift)

Turn ignition switch Off.
Remove T-case 20 amp fuse.
Wait a minimum of two minutes and 30 seconds, then replace fuse.
Cycle ignition switch On and Off 5 times.

Factoryjack
Oct 27, 2010.
When I turn the truck on the 2wd is on and not flashing.
When I switch to 4wdh the 4wdh light flashes and only that light.
When I swtch to 4lo the 4lo light flashes and only that light.
They will keep flashing until I switch back to 2wd.
They are not flashing any codes it is just a constant flash.

Ok, I installed a jumper in the DLC on #13 to ground and swtched the truck on. The 2wd light will flash very dimly and then about a second later all three will flash one time 2wd, 4h, and 4L there is about a five second interval between the flashs. I can bearly see the 2wd flash before all three light flash. I'm not sure if that dim flash even means anything.

I also removed the t-case fuse per the instructions and switched the truck on and off 5 times. Nothing happened.

Tiny
1996z71
Nov 2, 2010.

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