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Discussion Starter · #1 ·
Can a front actuator be bad and still work? My light came on when useing 4x4 (although 4x4 still worked). took to the shop and they said the TCM code showed a bad front diff actuator. But they - and myself - verified it seemed to engage and disengage properly. So they cleared the code. LIght is now back on...4x4 still works and disengages. Don't want to waste money on new front actuator if u guys think there is a different problem. What do u think?
 

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It's possible.
The operated actuator will return a signal saying that it is operated.
If the control unit doesn't receive the signal it won't operate the clutches to send power forward.
I think the signal wire is black and white and I think it should have 12volts when returning the signal.
The actuator may be fine, the wire may be damaged and the signal is leaving the actuator but not reaching the control module. Under the truck is a nasty environment for electrical wires.
 

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Discussion Starter · #4 ·
Yeah the first thing I did was clean all the ground connections as per a common problem for these...but it's a tx truck, no rust...didn't change anything. But I'm not sure what you mean that it won't send the power forward...my 4x4 system indeed works. I was in wet grass yesterday going up a slope, back tires started to slip, put in 4wd, service light came on but still went into 4wd. Up the slope I went. And that is my dilemma...4wd system seems to work perfectly.
 

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Ok, I guess we need to know the code(s) that are being generated, the OBD2 codes that are attached to the Service 4wd message.
 

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Discussion Starter · #6 ·
The 'service 4wd' codes are stored in the tccm which can only be pulled from an 'enhanced' scan tool. But my mechanic said the code was related to a bad front actuator.
 

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A $150 scanner will retrieve those codes, most parts store (those that want to sell actuators) will be able to read the codes.
 

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Discussion Starter · #8 ·
Are there multiple different codes that can indicate a bad front actuator? If so, I can investigate. But if only one code then really no need to go down this path.
 

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2001 GMC Sierra SLE 2500HD , AT , 6.0 , 4x4 extra cab
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Are there multiple different codes that can indicate a bad front actuator? If so, I can investigate. But if only one code then really no need to go down this path.
What I would do [ suggest ] is get a wiring diagram , and double check that is for specific truck , not something close .
You count how many wires , take note of the color codes , then go to the control unit [ 4 wheel drive control ] and match the wires to control unit , the diagram should show this as a box / rectangle lines , inside the box should be 1st incials of each circuit 4x4 sense , 4x4 act , 4x4 gnd , 4x4 pwr , etc.
For most computer controlled devices [ things may have changed some in the last 15 yrs ;) - the grounds control & sense , the Positive is on with KOER - Key On Engine Run , grounds are common for sensor & actuator .
Check each circuit to function , repair as needed , then use a logic probe to test all circuits in the actuator .

A lot of this stuff I will take apart and service or repair , even circuit boards , let along connectors - especially if the cost is worth my time [ that varies both for myself & customers - that can be some kind of flat rate ;)

Could be just sticky moving parts .
 

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Discussion Starter · #11 ·
I bought a front actuator. I don't need to clear any codes first do i? I have read somewhere else that if the service 4wd message comes on, all u have to do is hit the reset button. Codes are stored in computer but service message will not come back on the dash unless there is a problem again. Does anyone know for sure?
 
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