2001 GMC Jimmy, 125,000Kms. Automatic with 4 button 4wd.

Was driving down the street yesturday, and had my vehicle go into 4LO while I was at a stop light (good thing I noticed the lights flashing).

From then on, I can only get my truck into Auto 4WD or 4LO.
If I press 2HI it just goes into 4LO
If I press 4HI it does NOTHING.

Tommorow I will be tracing all my Vac lines, and checking everything posted in the 4x4 No Workie thread.

Im just fishing for people who might have had this exact problem, or who know what i need to replace/fix.

Thanks,

- Bill

 

I would start by pulling the passenger side kick panel and having a look at the electrical connection on the TCCM (transfer case control module). When there are erratic problems with the 4wd system, it is likely caused by corrosion in the electrical connection at the TCCM.

 

Alright, update time.

Checked out the TCCM.
Took it out, checked the connections.

The Orange cable (on the power harnesss I assume) was corroded to hell and back. I spent some time cleaning the socket and the connector on both the harness and the TCCM.



Went through all the data connections on the other plug, 1 of them was corroded, so I fixed the pin and the socket on that one.

Hooked it back up, and oooh.

I can change out of Auto 4WD to 2 HI, and it was intermittantly allowing me to change to the 4Lo and 4Hi modes. (all of which were acompanied by the normal sounds of the transfercases and such changing positions)

Went for a test drive to get a coffee, only works on 2HI now, the buttons on the dash give me no response when I press them. It wont go into Neutral (holding 2HI and 4LO down for 15 secs) either.

Could the buttons be broken? or something to do with the resistances that the modules want?
I think this is mostly an electrical problem, am I correct in assuming this?

Any more ideas? (I have pic's of what I did today to write it up in a psuedo guide if anyone is interested)

- Bill

[IMG]local://upfiles/11771/98F626D617CE435CB17FF405ADEEA7E6.jpg[/IMG]

 

Another Update:

Back to the original Behavior.

Auto 4WD and 4LO.

I can get it to go into 2HI and stay there if I pull the fuse under the hood.

No codes in the computer either, even with the Service 4WD light on.
I used this code reader: http://www.iequus.com/product_info.php?product_id=3110&category_id=1 _10_7

Help?

 

That scan tool cannot read Chassis codes (Cxxxx) which is what would result from the Auto4wd TCCM if/when it had stored codes.

The dirty connections were not helping anything, but you may want to try actually removing the pins from the plastic connector one at a time and really getting into them to mechanically clean them, then massage the contact for greater pressure against the pin. Once you are done with that, coat the connector with some dielectric grease to protect the now clean contacts.

If the connections are all good, then there are a few possibilities for the random engagement of 4HI/LO/Auto4HI. One is that there is a small vacuum leak that is affecting the engagement of the front axle. This could be a failed vacuum switch on the top/side of the transfer case or an actual broken/cracked line. Another is the possibility of the encoder motor position sensor starting to go bad.

 

Took appart the TCCM again, cleaned all the leads, male and female ends all taken apart and put back together. (No Die-electric grease on hand)

Took the dash switches out cleaned, and re-assembled.

Still the same behavior.

Should I pull the negative from the battery for 30mins? or pull a couple fuses to force a reset?

Im thinking Bad TCCM at the moment. Im trying to wrangle up someone elses to test.