4X4 troubleshooting

Tiny
DAPHNIESMAN04
  • MEMBER
  • 1999 GMC JIMMY
  • 4.3L
  • V6
  • 4WD
  • AUTOMATIC
  • 102,000 MILES
The vehicle listed above has a 4 button electronic switch for four wheel drive. When I click on any setting other than 2 hi I just get a blinking light. I can hear it click under the truck but the light flashes. Now I have a service 4wd light on. No codes picked up with my reader. I replaced all of the obvious vacuum lines first. I don't know how to check/diagnose the vacuum solenoid on the firewall nor how to check the check valve that is in line. But I did manage to break the nipple off of the vacuum reservoir that is located inside the fender. I tried to glue that nipple back into the reservoir but I don't know if that is wise or if it is even necessary. I've seen some guys cap it off. Not sure what to do next.
Saturday, July 11th, 2020 AT 11:32 AM

19 Replies

Tiny
94 TRANSAM
  • MECHANIC
  • 680 POSTS
This is probably a bad hub lock actuator on the front axle. Check for vacuum leaks on the hoses. You can also remove it and apply vacuum and make sure it is working though it probably has a ruptured diaphragm.

Rich
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Saturday, July 11th, 2020 AT 12:12 PM
Tiny
DAPHNIESMAN04
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  • 13 POSTS
Are you referring to the part under the battery cover?
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Saturday, July 11th, 2020 AT 12:36 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Good afternoon.

There is a code stored in the system but most code readers will not access the transfer case module.

There is a motor on the case that needs to operate when you command changes from 2 to 4 and back again. that motor is a common failure.

I attached a wiring diagram for you to view as some checks need to be done. Please test all the fuse in the diagram for power on both sides.

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

https://www.2carpros.com/articles/how-to-check-a-car-fuse

That vacuum tank must be fixed as it is critical to the operation of the system.

Roy

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Saturday, July 11th, 2020 AT 12:45 PM
Tiny
DAPHNIESMAN04
  • MEMBER
  • 13 POSTS
I have to find a new vacuum reservoir/canister I guess. Advance does not have one.
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Saturday, July 11th, 2020 AT 1:12 PM
Tiny
ASEMASTER6371
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Correct. They will not have that. That will be either Dorman part or GM.

I just checked with Dorman and they do not have one listed.

I checked wit GMparts direct and they do not list it anymore.

Roy
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Saturday, July 11th, 2020 AT 2:29 PM
Tiny
DAPHNIESMAN04
  • MEMBER
  • 13 POSTS
I pulled the fuses. They all look intact. I got epoxy and repaired the nipple on that canister. I've noticed fuel economy not as good as before. I'm not sure if this matters but my A/C is coming out of my defrost and my vents no matter what position I place the dial inside. About a year ago I had to remove my dashboard to repair a leak that developed up under the wiper cowling up against the firewall/bulkhead. I'm not sure if the A/C has been coming out like this or not. I can't remember. I don't drive my venicle very often because I have a company car. But now my daughter has her license so I need the wheels.
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Saturday, July 11th, 2020 AT 4:43 PM
Tiny
ASEMASTER6371
  • MECHANIC
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In my previous post I asked you to check the fuses for power. This is not a visual test but a power test at the fuse box.

As far as the vacuum, is there vacuum coming out of the canister to the dash? There should be vacuum at port 6 of the control head. Verify that as well.

Roy
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Saturday, July 11th, 2020 AT 5:06 PM
Tiny
DAPHNIESMAN04
  • MEMBER
  • 13 POSTS
I took my test your light grounded it and check both sides of each of the four fuses and all four show power. As far as the vacuum on port 6 I don't even know where a port 6 is. The only canister that I know of is the one inside the fender that I broke and fixed, but it only had one port on it.
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Saturday, July 11th, 2020 AT 5:52 PM
Tiny
DAPHNIESMAN04
  • MEMBER
  • 13 POSTS
Ah, I'm an idiot. Sorry control head, as in the dash. I will check it in the daylight, sorry for my lack of understanding the terminology.
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Saturday, July 11th, 2020 AT 5:55 PM
Tiny
ASEMASTER6371
  • MECHANIC
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No problem.

Let me know the results.

Also, was fuse 15 in the instrument panel fuse block one of the fuses you tested?

Roy
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Sunday, July 12th, 2020 AT 3:30 AM
Tiny
DAPHNIESMAN04
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Yes sir, I checked that fuse as well.
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Sunday, July 12th, 2020 AT 6:26 AM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, good.

In the first post, I attached a diagram of the wires that power the module. Can you verify those powers at the module to be sure you do not have a wiring issue?

Also, when you command 2 or 4 wheel, can you verify power to the motor on the case? I highlighted the 2 wires for the motor.

Roy
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Sunday, July 12th, 2020 AT 6:58 AM
Tiny
DAPHNIESMAN04
  • MEMBER
  • 13 POSTS
Sorry, I have been crazy busy at work. I'll try to get time to look at it this weekend.
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Wednesday, July 22nd, 2020 AT 2:43 PM
Tiny
DAPHNIESMAN04
  • MEMBER
  • 13 POSTS
Okay, I made some time. I turned my ignition to on (not running) probed the plug on the axle and on the brown wire it showed 11.43v. On the black wire with white stripe it showed.43 v.
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Wednesday, July 22nd, 2020 AT 3:46 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, was that with the connector off the motor? If it was plug it back in and check the black wire again. Back probe it for voltage.

Roy
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Wednesday, July 22nd, 2020 AT 4:03 PM
Tiny
DAPHNIESMAN04
  • MEMBER
  • 13 POSTS
Okay, I put back on and got a.16v.
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Wednesday, July 22nd, 2020 AT 4:31 PM
Tiny
ASEMASTER6371
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Okay, based on that result, the motor itself is bad.

Replace the motor.

Roy
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Wednesday, July 22nd, 2020 AT 4:35 PM
Tiny
DAPHNIESMAN04
  • MEMBER
  • 13 POSTS
Thanks, I will attempt that next. As far as the other vacuum issues and the A/C coming out of the same vent regardless of what position should I start a new thread?
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Wednesday, July 22nd, 2020 AT 4:54 PM
Tiny
ASEMASTER6371
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You are welcome.

Yes, please.

Roy
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Wednesday, July 22nd, 2020 AT 5:01 PM

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