what controls front axle actuator

malibu795

misspeelleerr
Apr 28, 2007
7,855
284
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in the buckeye state
I have a mechanical shift t case.. There is a 3 wire plug right above the selector shaft.. Educated guess tells someone whether tcase is in 4L/N/2/4H.

Front axle actuator is not working.. Replaced it same results.. Front drive shaft spine.. Wheels don't. And 4x4 light doesn't come on.

Something is telling the TCM the tcase is in 4L because I don't get wrong ratio codes when I drive it in 4L

Any help?
 

Noreaster

Active member
Jun 13, 2007
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Cape Cod,MA
looked back in some of my saved stuff when I had an issue with 4wd

When the ignition switch is placed in the run position and the 4WD control lever is in the 4WD position, the transfer case switch closes, supplying a ground to the 4WD relay coil supply voltage circuit. With the ground applied, the logic of the front axle actuator actuates a DC motor to engage the front axle and supply voltage to the Four Wheel Drive (4WD) engaged signal circuit. The 4WD engaged signal circuit notifies the PCM and the Anti-Lock Brake System that the vehicle is in the 4WD mode. The 4WD indicator is commanded on via a Class 2 serial data signal from the PCM. When the 4WD control lever is in the 4WD Low range position, the transfer case switch closes and supplies a ground on the 4WD low signal circuit. This informs the PCM that the vehicle transfer case is in Low range. When the vehicle is in Low range, the PCM changes the shift pattern of the automatic transmission.
 

juddski88

Freedom Diesel
Jul 1, 2008
4,651
116
63
Chesterfield, Mass.
In my experience, if you already replaced the actuator and checked fuse, it's usually a worn switch on the tcase. I found a supplier in Arkansas and bought a few because they are dumb expensive through gm
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
21,171
4,953
113
Phoenix Az
And guys who have a switch on the actuator wiring to keep it off to gain "2 low" for backing trailers up. That's on my list of things to do
 

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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ZEPHYRHILLS, FL
If it's anything like my 01's was, it is a REAL basic system just like GM has used since 97 for the most part(88-96 was simliar but GM changed to the electric servo instead of thermo electric sometime in 97). The transfer case switch has 3 pins in it. A is ground, B is grounded internally in the switch when you go to 4 low, and C is grounded to A when you move it out of 2 high. The front axle actuator has 4 wires in it, A is the signal wire to the ECM, TCCM, ABS, and so on to tell it when it is in 4X4, and is powered from C. B is the pin that gets grounded by the transfer case control switch to enagge the actuator. C is the 12V+ keyed on power source to the front axle actuator that powers it. And E is the ground(The ground for E is also the same ground for the transfer case control switch).
 

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