4 Wheel Drive Selector Switch went Crazy!!!

Djordan2

Original poster
Member
Feb 5, 2012
46
Hi all.. This morning I got into my Trailblazer and Turned the truck on and on the 4 Wheel drive selector switch the yellow
2WD light was flashing and the red N was lit up..The truck was still in park. I put the truck in reverse and the lights were still the same
so I backed out of the driveway (No issues there) after backing I put the truck in drive to continue to work and everyting went to normal
I didnt notice anything out of the ordinary, no Service light so Im a little confused!!!!
 

RayVoy

Member
Nov 20, 2011
939
You could be having trouble with the Transfer Case Control Module (TCCM), but likely it is the switch.

The switch is just a bank of rotary contacts and the metal surfaces will oxidize.

Twist the switch from left stop to right stop 50 or 60 times, the wiping motion should clean the contacts.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
2002 models did indeed have a bad batch of TCCMs, but the red "N" is a big clue for your incident. The switch isn't actually a set of separate contacts for each mode with a separate wire back to the control module. It's like a potentiometer (volume control) with only five different volume levels. And the signal (resistance) is carried on only two wires back to the TCCM. So the GM designers had a choice - which direction should the OPEN circuit condition be a signal for? Because a switch is more likely to go open (high resistance) from dirty contacts or a broken wire then to a SHORT, or a low resistance indication. Which direction shoulf the GM designers have chosen - 2HI (the safest mode that everybody can limp home in if the circuit has a fault) or NEUTRAL?

Yep - they chose "N" as the mode that gets commanded if the switch goes open. Goofballs.

The switch was redesigned around 2005 to be more reliable and cheaper. If the cleaning process doesn't work reliably for you, just go to the dealer. They're under $30.
 

Mark20

Member
Dec 6, 2011
1,630
I've had mine do some funky things so I engage AWD & 4H once a month to exercise the system. I unfortunately don't remember to cycle the switch to 4L & N.
 

Djordan2

Original poster
Member
Feb 5, 2012
46
the roadie said:
2002 models did indeed have a bad batch of TCCMs, but the red "N" is a big clue for your incident. The switch isn't actually a set of separate contacts for each mode with a separate wire back to the control module. It's like a potentiometer (volume control) with only five different volume levels. And the signal (resistance) is carried on only two wires back to the TCCM. So the GM designers had a choice - which direction should the OPEN circuit condition be a signal for? Because a switch is more likely to go open (high resistance) from dirty contacts or a broken wire then to a SHORT, or a low resistance indication. Which direction shoulf the GM designers have chosen - 2HI (the safest mode that everybody can limp home in if the circuit has a fault) or NEUTRAL?

Yep - they chose "N" as the mode that gets commanded if the switch goes open. Goofballs.

The switch was redesigned around 2005 to be more reliable and cheaper. If the cleaning process doesn't work reliably for you, just go to the dealer. They're under $30.

This is what I was thinking as well Thanks for all your input Guys.. Ill Try the Contact cleaning first because I have to admit I might have switched The 4WD
twice since I bought it in 2002... and I havent seen it do this before and being that it went into gear fine in reverse and drive so Again thanks a tong fellas!!!!!!!
 

RayVoy

Member
Nov 20, 2011
939
Djordan2 said:
This is what I was thinking as well Thanks for all your input Guys.. Ill Try the Contact cleaning first because I have to admit I might have switched The 4WD
twice since I bought it in 2002... and I havent seen it do this before and being that it went into gear fine in reverse and drive so Again thanks a tong fellas!!!!!!!
Not a lot of 4x4 requirement in SC, but occasionally, switching into and out of 4x4 is good for the numerous parts. Should be done a few times a year.

In NB, we get a few opportunities to need 4x4 after an ice/snow storm, but like you guys in the south, I need to remind myself to exercise it in the dry months.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
For anybody else reading this - TEST your switch and 4WD system every month if you want it to be there for you when you really need it. The front axle actuator and transfer case encoder motor can also freeze solid if never exercised. If for no other reasonthan to increase your resale value when you sell the 4WD you really didn't need in the first place. :wink:
 
Feb 24, 2012
133
I always put my truck into 4lo when I drive up ramps. Half for the excersizing of parts, half for the fun of all that torque... But rarely do I need to use ramps. I can just roll underneath with a creeper...
 

Mark20

Member
Dec 6, 2011
1,630
the roadie said:
For anybody else reading this - TEST your switch and 4WD system every month if you want it to be there for you when you really need it. The front axle actuator and transfer case encoder motor can also freeze solid if never exercised. If for no other reasonthan to increase your resale value when you sell the 4WD you really didn't need in the first place. :wink:

:iagree:
 

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