Four wheel drive does not work

RKP209

MEMBER
1994 GMC SONOMA
4.3L
V6
4WD
AUTOMATIC
92,000 MILES

When I push the 4HI button nothing happens. I've checked the fuse, it's good, checked the fuse for power and it has power. The 2HI light is lit but nothing happens when I hit the 4HI button. No flashing, nothing. When the transfer case shift motor when out in the past, the 4HI button light would flash and then go back to lighting the 2HI button light. I installed a new push button switch thinking that was the problem and did not solve the issue. Is there a relay to the shift motor?

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,179 POSTS

Hi,

If the switch is new and not responding and you made sure there is power to and from the fuses, the next thing to check would be a circuit ground.

There are several grounds spliced together from the shift module. Check to see if there is continuity to ground at those wires.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

I attached the wiring schematic below for the 4wd circuit. I had to cut the pic in half to make it readable for you. I did overlap them so you can follow from one to the next.

Let me know what you find or if you have other questions.

Take care,

Joe

See pics below.

Images (Click to make bigger)