4 Wheel Drive Diagnostics

loulblades

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I ran across this troubleshooting guide for 4 wheel drive from another source. I cleaned it up a bit and reformatted it some. It is in a Microsoft Word format
 

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jwpotts0413

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interesting, i did not know you could determine DTC (diagnostic trouble codes) without an OBD II scanner. that file provides instructions on how to make the 4x4 buttons blink in a "Morse Code" like fashion to reveal any trouble codes concerning the 4x4 system. very cool!

haven't tried it, but if it's accurate that is a great find.
 

mross

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i can't get the word document to open,is there another link around with this info?
 

leatherneck

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diagnostics codes

loulblades,
I've went through your word document and it looks very promising for troubleshooting the electric version of tahoes 4x4. As for my self i consider my self to be some what knowledable about cars and electricity. So I'm coming to you for your opinion on a matter of my 4x4 recently my 4x4 has gone out the 4hi and 4lo blink constantly when i try to engage it. i can hear the soleniod engage but i can tell its not in 4wheel drive. so i put it on a lift then engaged the 4hi and again i can hear the soleniod engage on the transfer case plus the front driveshaft also starts to spin but of course the wheels are doing nothing. So i took it a step further and checked to see if there was voltage at the front diff soleniod and yes there was so i assumed it was the soleniod gone bad. Then i go to a local junkyard and replace it with another one and what happens the same thing. But i do notice when i manually engage the front diff the 4hi indicator light stays on and the front wheels spin and switch does not blink making me think that the other electical plug on the front diff is the indicator for the switch on the dash. So do i just have bad luck and grabbed a bad front soleniod from a junkyard that cost me 5 bucks or is there something else i'm missing. When i tested the other soleniod i did not install it first time instead plugged it in then had the 4hi button pushed i wanted to see if i can see the plunger stick out or not, i also tried it in the axle as well.. fuses were also checked and came out good with power running through them..

Your help on this matter is greatly appreciated.
R.Flores
Sgt./USMC
 

loulblades

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Since you said the light quit blinking when you manually engaged the front diff that let's you know that the fedback to the TCCM is good.

Also since you said there was another connecter on the diff, I am figuring this is the thermal solenoid type. There is a TSB to convert from the thermal to motor type. With the motor type the proximity sensor (second connector) is not used.

The thermal type are very prone to problems. If it is cold out they take longer to engage and sometimes don't. It wouldn't surprise my at all to pick one up in the junkyard that didn't work. They can be tested by applying 12 volts to it (again the thermal variety). The motor type is a little more complex.

Of course I said all this without knowing the year of your truck. Pre January 96 Tahoes had the thermal types as far as I know unless they were converted.

Hope this helps.
 

leatherneck

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thermal

Ah yes just a couple of things i forgot to mention that you reminded me on your post.
Well first of all My TAHOE is a 97 second of all i thought about that not knowing if it was thremal or not i went ahead and tried warming up the soleniod but still nothing. you stated something about a different type actuator the motor type HMM might be something i want to look into. I'm trying to get all the lil bugs and stuff out the truck before i deploy next year so that way it doesn't worry my wife . thanks again..
 

loulblades

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This is not what I was referring to. The Posi-Lok is used to get rid of the actuator and manually engage the front diff.

The motor type actuator requires 12 volts all the time (when ignition is on). 12 volts is applied to cause the actuator to engage and the other pin on the connector is the feedback to the TCCM (transfer case control module) to let it know the diff is engaged.

If you put the Posi-Lok in, you don't have to worry about actuators any more.
 

leatherneck

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12vdc actuator ??

Oh ok well in that case i need a lil help in guiding me to the right direction on that one. Last night i really couldn't sleep so i had found that posi-lok actuator for $179-202 but the more i was looking into it and at it I was thinking well if i can find an 12vdc actuator that can push that pin in then i'll fabricate a bracket and some sort of rubber gromet to stuff inside the hole where the soleniod was. Anyways i really didn't find anything but if you got something a pic or website then please shoot it my way so that way i can look more into it.
 

loulblades

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Look above the actuator on the diff to see if there is a 2 pin connector. This is what is used on the thermal actuator type to determine if the diff is actually engaged or not.

I think that since your truck is a 97 it should have the motor type actuator. I believe that 96 was the last year that the thermal actuator was used on 1/2 ton trucks but I can't state that as a fact, someone else may know.

The actuator is available at an auto parts for less than $100.
 

leatherneck

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pin

both the plug that connects to the actuator and the plug that sends the signal to the tccm acknowledging it is in 4x4 have 2 pins just one plug is wider than the other .. I've priced the actuator its about $50-70 depending on where i take it..i might just go ahead and replace it new and call it a day.. but the truck does have 137k and was originally from jersy used as a snow plow, when i bought it the truck had 87k since then i have put down some ruff miles on it through the mud in North Carolina and the sands in Florida, now im here in Cali.
 

loulblades

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Then it is the thermal type.

As I said, they are prone to failure and there is a TSB to convert to the more reliable motor type actuator. I don't have the number in front of me but there is a small amount of wiring to do.

Remove old connector.

The new connector has a wire for 12 V to the actuator (hot side of transfer case switch).

Splice to the wire to run the actuator (this comes from the switched side of the transfer case switch).

Splice to the feedback to the TCCM.

If you are not keeping it for another 50K and you are not running in cold weather, just putting in another thermal actuator might be the best bet.
 

leatherneck

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fabrication

ok so your talking about thermal actuator, i figured it be my luck well the truck is a d**n good truck so i'm keeping it and giving it to my boy in 15 years lol. But anyways as for the motor actuator i'm sure if i can see what it looks like and how it is wired then i can get it from there. Cause i know i can get the 12vdc whenever i push the 4x4 button. next question i'm gonna try to throw your way what about fabricating a pin that would keep the 4x4 engaged at all times and keep the front drive shaft spinning at all times but no power until actually engaging the transfer case. Will that affect the longevity of the front diff. I'm guessing no because there will be no actual power going to the front axle but then again theres no telling. So heres what i got for a fabrication i tore apart the old thermal actuator down to the bare bolt and this is what i got.
[/ATTACH][/ATTACH]

so i figure with that i can find a bolt big enough to fit inside the actuator housing and long enough to push in the pin once the actuator housing is threaded into the front diff. and using a nut to keep the bolt from backing out the actuator housing. similar to thishttp://www.autozone.com/autozone/catalog/parts/partsProduct.jsp?skuDescription=Duralast+/+Four+Wheel+Drive+Actuators&categoryDisplayName=Drivetrain&fromString=search&itemIdentifier=860640_131728_0_&productId=860640&sortType=&parentId=12-0&filterByKeyWord=actuator&isSearchByPartNumber=false&navValue=11201483&categoryNValue=11299999&fromWhere=&itemId=1483-0&displayName=Four+Wheel+Drive+Actuators&store=3351&searchText=actuator&brandName=Duralast
 

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loulblades

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There would be extra wear and tear if the diff is engaged all the time. Also a decrease in gas mileage.

TSB 76-43-01A is what I referred to for updating to the motor actuator.

I see that 97s also had thermal actuators.

I also see Autozone lists both the thermal and motor actuator.

http://www.autozone.com/autozone/ca...Value=&categoryDisplayName=&_requestid=146426

(Hope that link comes through)

I personally wouldn't keep the front diff engaged all the time but that's me.
 

leatherneck

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yep

You see i was thinking the same thing but hoping you might not be . oh well i'll take a look further into that motor actuator for sure though..
 

leatherneck

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got it

well i went ahead and did it went back to old thermal switch i bought @ Kragen(oriely) for 60 bucks i saw the motor type with the 5 pins it but i needed that thing in a flash i took the tahoe out on a hiking trail with a f350 on 38 M/T' s diesel leading the way. It was my first experience up a mountain that was very narrow and rocky and scary at times but none the less the tahoe kept up with a times of bottoming out on a few big rocks and my nitto terra grapplers A/T held up to the challege in 4lo. so i felt pretty good about the only thing i didnt like was coming back down and then after washing the Tahoe seeing all the damn scratches from the brush but a small price to pay for a lil family time of fun
 

loulblades

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If you want to play...you must pay. Generally the scratches from brush will rub out pretty easily.
 

BobGTahoe

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You seem to be pretty familiar with this issue. I have a 97 that had the thermal actuator. Got a motor actuator and wiring harness and tried to hook it up tonight. First problem, the two prong connector on the new harness that I assume is meant to connect to the existing wiring for the thermal actuator is slightly different than the connector on the frame and won't connect. Just to test, we try to connect the wires to see if it will work. No luck. The other problem we have is we don't know what the long brown wire is for. Supposed to go to "CKT 241 (BRN) BETWEEN CONNECTORS C120 AND C100". Without a wiring diagram, it's hard to know where this is.

Do you know what this wire is for?

Can you tell me where to connect it?

Thanks in advance. Appreciate your help to others that I've been reading.
 

loulblades

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I do have a copy of the wiring diagram for the new harness at home so I will look for it tonight.

So I will tell you what I can for now.

The long brown wire connects to the hot side of the transfer case switch.

The 2 pin connector, if I am recalling correctly, connects to the proximity sensor wires (unplug the connector that goes to the sensor which is located above the actuator on the diff).

Unlike the thermal actuator, the motor type requires voltage to engage and disengage and that is what the brown wire provides. In reality you could connect it to any fused IGN source.
 

loulblades

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Sorry it took so long to get back to you. I don't know if you got this worked out.

I found my wiring diagram which was faxed to me and I can barely read it so trying to scan and forward would be futile.

What I can tell you is this:

The 2 pin connector that came on the new wiring harness plugs into the cable that was connected to the thermal actuator (black and light blu wires). If the connectors won't mate for some reason then cutting and splicing is in order.

Cut the connector off that went to the sensor on the diff and splice the black/white wire from the new connector to the black/white wire that went to the old connector. Tape off the other wire that went to the old connector.

And the brown wire was as previously mentioned.

May the force be with you.
 
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