Hi i have a 2002 gmc sierra diesel and i was driving down the road and the security light came on and the truck put it into 4low and wouldn't come out. I drove it home in 4 low and started looking into it and still can't figure it out. I hooked up my scan tool to it and I got codes PO500, PO700, PO836, PO2106 one was for vehicle speed sensor and another was for transmission fault and the other two it didn't say what it was for. When i push the button to put it in 2 wheel drive nothing happens. It dosen't even try to do it. Let me know what you guys think. It seems like the truck is in anti theft mode but it still lets me start the truck. I appreciate the help
Josh

The 4wd switch panels are known to go faulty, also nsbu switch on trans when wet. Also check your transfer case for leaks/fluid level. If it's run dry its likely hamburger inside.

I will check that stuff out. Last time i checked the t-case it was good. also i think it has something to do with the security because the security light will flash at me and than it put it into 4 low all on its own weird
thanks

There is a sensor in the encoder motor on the side of the t/case that goes bad. Reads one thing....displays another. I bet you have t/case codes, but your programmer just won't read them.

is there anyother way to get it out of 4low. i will have to check that sensor to see if its good. Where can i see what all of my check enging light codes mean. I didn't have a up to date cartridge in my scan tool so i couldn't see what to mean't PO836, and PO2106

There was a thread on another site about the ground on the drivers side front body mount deteriorating and causing transfer case and 4wd module problems. There are 2 different sizeable wires that are grounded there. I need to check these on mine too, as I am having similar problems. You might also have a c0327 code which is for the transfer case range select. Mine clears up on its own with letting it sit for a little bit(key cycles), but comes back again randomly.

I think you are on to something, I did have that ground wire off i wonder if i didn't tighten it up all the way... I will have to double check that tomorrow and i will let you know.

I made sure that ground wire was tight and still have the same problem.. Is there anyway to get it out of 4 low or what would you guys recommend me to do. Also do you know what these codes mean po2106 and po836
thanks,
josh

P2106 comes up dry, but P0836 is a trans code set when there is a t.case selection error.

Document ID# 1477530
2002 Chevrolet Chevy K Silverado - 4WD
DTC P0836

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1477530&psdid=271&evc=sm#ss1-1477530">Circuit Description

The 4WD low signal is used to notify the transmission control module (TCM) that the vehicle is in 4WD low range.
DTC P0836 is a type B DTC.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1477530&psdid=271&evc=sm#ss2-1477530">Conditions for Running the DTC

• DTCs P0721 and P0722 are not active.
• The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
• Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
• Output speed is greater than 60 RPM.
• Transmission fluid temperature is 20-130°C (68-266°F).
• The shift is complete and NEUTRAL range is not selected.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1477530&psdid=271&evc=sm#ss3-1477530">Conditions for Setting the DTC

DTC P0836 sets when one of the following conditions occur:
• The transfer case switch indicates high range, and the calculated range is low range for 5 seconds or greater.
• The transfer case switch indicates low range, and the calculated range is high range for 5 seconds or greater.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1477530&psdid=271&evc=sm#ss4-1477530">Action Taken When the DTC Sets

• The transmission control module (TCM) illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
• DTC P0836 will be stored in TCM history.
• The TCM inhibits torque converter clutch (TCC) engagement.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1477530&psdid=271&evc=sm#ss5-1477530">Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1477530&psdid=271&evc=sm#ss6-1477530">Diagnostic Aids

• Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
- A bent terminal
- A backed-out terminal
- A damaged terminal
- Poor terminal tension
- A chafed wire
- A broken wire inside the insulation
• When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
• You may have to drive the vehicle in order to experience a condition.
• Inspect for any transmission DTCs that may have set again.

Hope this helps.....just some quick info I came across....

thanks for the help. Those codes came up when the truck put it self into 4 low when i was driving down the road. It grinded really bad i cam to a quick complete stop than it locked in to 4low and now it won't come out. The switch lights do lite up but it dosen't do anything when i press 2 hi or 4hi.

also is there anyway of seeing why the service 4wd light is on with a scan tool

Also do you know what these codes mean po2106 and po836
thanks,
josh

Hey Josh, FYI: At the top of the Forum page is a sticky for DTC codes. :)

thankyou

I am wondering if my switch is bad because it dosen't even realize that i am pushing the button for 2hi, usually when you push the button the light will flash even if it is unable to go into four wheel drive, its just weird that it put the truck into 4low all on its own. Also i was messing around with it tonight it is in 4low but still in 2wheel drive.

I am wondering if my switch is bad because it dosen't even realize that i am pushing the button for 2hi, usually when you push the button the light will flash even if it is unable to go into four wheel drive, its just weird that it put the truck into 4low all on its own. Also i was messing around with it tonight it is in 4low but still in 2wheel drive.

I had a switch go bad, but it went with symptoms of not knowing what was selected. None of the lights would light up.

At the time +/- 4 years ago I paid $70 for the switch and changed it right there in the parking lot in about 5 minutes. The service 4wd light would come on randomly as well.

I would think that the pushbutton switch is what is causing yours to stay in 4low as there is no other place a transfer case shift could be commanded from. I wouldnt think a security issue would engage 4 low as a deterrent.

just my $0.02 (canadian)

Thanks, i think i might have to buy a switch. I am going to try to borrow one from a buddy first to see if that is the problem. I took mine apart and just realized that they still have the auto 4wd button just a different cover.

Try jacking all 4 tires off the ground. Now try shifting out of 4lo to N, then any other setting w/ tranny in P and/or N. It sounds like you're "locked" mechanically in 4lo, not electronically.

ok its worth a try. I am going to bring it down to my buddy today at a tranny shop, he gave me a switch to try but still didn't work. I don't know its weird

Well i jacked it up and tried putting it in 2hi and nothing happened. I brought it down to my buddy at the tranny shop and he hooked his modis up to it and it brought up code c0308 which is low voltage signal. I am going to check all the connections. I also pulled off the encoder motor on the t-case so i could manually put it in 2wd so i can drive it. He is going to get me a motor so i can try it and if that dosen't work i guess i will be spending 300 dollars on a module.

I read that you had messed with the ground wires earlier. Have you ground the frame down to bare metal and remade the ground?

I had brake issues and that cured it. Actually had them twice, a year apart, and new ground fixed them both times.

These trucks are picky about needing good ground connections. Then again, it could be the $300 module.

jb

yea i don't know i will double check. On the ground on the firewall there already is a studd that is welded on the firewall but i will double check.
thanks

Well here is the latest my buddy at a tranny shop gave me a t-case motor for 4wd and i tried that and it didn't work. So i figured the only other thing it could be is the 4wd module. I pulled it out tonight and looked on the back of it and there was a good old junk yard number written on it so its been replaced once and looks like this is a common problem. I seen that there is a service bulletin on the error code for 4x4 module so thats what i am going to have to buy.
Josh