Goes Into 4Wd On Its Own

Michael Owner/Technician Colorado Posted   Latest  
Unsolved
Drivetrain
2008 Chevrolet Silverado 1500 LT 5.3L (0 LMG) 4-spd (4L60-E) — 2GCEK19J481219982
Shifts Into 4 Wheel Drive On Its Own

Customer states the truck will go into 4wd by its self. Of course it wont do it for me., No codes are present. Any ideas on where to start? Any body seen this before? If it makes any difference he says it seems to happen on left turns. The lights on the selector do not change and works fine by turning the knob.

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William Technician
Illinois
William
 

A difficult one for sure. This switch works off a 5v reference and a resistance ladder built into the 4wd mode switch, so a simple short to ground will not cause this fault. The only logical fault is a faulty switch. On intermittent faults like these I advise the customer to take a video of the fault if possible. It protects them with evidence and myself as I can easily believe there is a real…

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Jared Diagnostician
Maryland
Jared
 

I've had encoder circuit issues cause this before. May be worth watching your encoder feedback PID(S) and see if it reads steadily.

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Anthony Owner/Technician
Pennsylvania
Anthony
 

I had a 2002 trailblazer that would put the transfer case into Neutral by it's self the dealer reprogramed it and it stop doing that but would gone in to 4wd randomly turn knob to 4wd then back to 2wd and it would go back to 2wd maybe have transfer case programing updated

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Eric Manager
Arizona
Eric
 

The encoder motor has a hold side that will let loose at times. Usually replace encoder motor but hard to prove. Also sometimes the position sensor in encoder goes bad and thinks it is in the wrong gear and will move on its own. Have also done a fair amount of switches. My approach is to ask the customer if want to try both switch and encoder assembly or wait until worse.

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Rusty Owner/Technician
Massachusetts
Rusty
 

I’ll assume they believe it’s going into 4WD. Because of some binding or resistance that they feel Or something they hear perhaps?? If it has traction control, I might suspect a WSS issue Given that it only happens on a left turn.

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Martin Instructor
British Columbia
Martin
   

Michael, apart from the suggestions so far, it may be possible to engage 4WD on some transfer cases, if there is a broken snap ring on the output shaft under some situations depending which transfer case is installed. The shaft with gear train then slides forward through the synchro sleeve, with the same results as shifting into 4WD intentionally. Without any disassembly, a quick check for a…

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Glenn Owner/Technician
Texas
Glenn
 

Hi Michael, What they may be perceiving as the 4-wheel drive having a mind of its own may very likely be an outer axle joint starting to seize up. It will create the same ‘wheel hop’ affect when turning like it is in 4-wheel drive. This problem will come and go, but it is best to duplicate the issue before you start digging into it. A quick inspection and cleaning of the front ABS sensors may…

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Lee Owner/Technician
Michigan
Lee
 

Following

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Robert Technician
Michigan
Robert
 

ATRA and the Trans Digest should give you some information not sure what RPO or splines you have but they are all listed . - MP3023, RPO code NQH, 2ML70 trans, 32 input splines, 32 output splines, automatic electric shift, half-ton truck, light-duty

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Andrew Technician
Utah
Andrew
 

This is a time to ask the customer EXACTLY what the truck is doing. Is it shifting into 4 wheel drive complete with transfer case thunk? Is only the indicator coming on? Does it feel like it is in 4WD with no other symptoms? If it is indeed actually shifting into 4WD does selecting 2WD cause it to shift back out?

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Randall Technician
Pennsylvania
Randall
 

Michael, Interestingly I looked at a 2006 Dodge Dakota today with the exact same complaint. I believe that Chrysler uses a New Process Gear transfer case that is similar to GM. It was the second visit for this truck as the owner wasn’t clear about the symptoms. I did scan the FCM, during the road test I observed the erratic encoder activity in the photo. No code, no wiring, connector or…

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Mark Engineer
Colorado
Mark
 

Michael Today I take care of a fleet of Suburbans and back then took care of a fleet of suburbans a decade ago. Often the driver would complain of the vehicle going into 4WD on its own What I finally figured out is the driver was reaching for the headlight switch which is a round knob right next to the 4WD knob (they are both round and next to each other). How I finally figured it out was a…

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Todd Diagnostician
Michigan
Todd
 

I had this happen on a 2008 Trailblazer and found a loose ground terminal at the transfer case control module connector. When the ground potential changed, the module would interpret it as a shift request. I found it by wiggling the transfer case control module connector while watching the lights on the switch, I found they would flicker when the connector was manipulated.

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Tamiyal Educator
Florida
Tamiyal
 

Lots of great input!!! Please let us know the outcome.

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