Question about 2001 GMC Jimmy
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Posted on Jan 02, 2017
SOURCE: four wheel won't engage
Theres a vacume dash pot under the battery box. It pulls a cable that engages the front diff. Put the vacume line and you'll have lights and four wheel drive. (it happened to my blazzer)
Posted on Dec 29, 2008
try going into reverse for 10 feet then go to drive for 10 feet that might help if not it is to the wiring to you 4x4 engage system (wires to your wheel hub)
Posted on Jul 04, 2009
On the full size, the front actuator is electric, not vacuum.
When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the front differential - it looks like a large bullet that threads into the front diff.) If it has 12 volts, the actuator is the problem. If it does not have 12 volts, check the transfer case switch and the power feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.
If I were you, I would buy a new heated actuator. They are available at most auto parts stores, and are about $90. They are also on eBay for about $55 plus shipping. These are very easy to change - just thread out the old one, and thread in a new one.
Good luck. The actuator is usually the problem 90% of time but recheck all of the wire harness just to maker sure there is no short before replacing any parts.
Posted on Jan 02, 2010
Testimonial: "This is exactly the info i need to troubleshoot and repair efficiently complete with wire numbers and colors thanks for the help buddy"
Good Evening. So from the sounds of it you say the hubs are not engaging, which means you probably checked the driveshaft and saw it moving. There is a actuator on the right hand side of your front differential and has plug in with 2 wires going to it. First off take a test light and hook it between the wires start the truck and be sure it is in 4wd and if the light turns on you need to replace the actuator which is a common replacement item. We only use the 88 and newer chevrolet trucks for our snow plows so I have seen this too many times. If there is no power there is a fuse in the fuse panel then take your test light and check them as well. I hope this helps you.
Posted on Aug 11, 2010
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