Question about 2004 Chevrolet Suburban

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At start up if you dont verify that the transfer case is in 2wd, sometimes it will automaticly shift on its own to 4wd or auto 4wd or 4wd lo. only just as the car is started will it change,never while driving, and it does this frequently for about two weeks then it goes away for about two weeks, then it starts doing it all over again.

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  • gary crawford Apr 06, 2011

    when I said at startup I should have said when you turn on the key, not even turning the motor over. you said possible poor connections. where exactly are these on trans and diff? thanks gary

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  • Chevrolet Master
  • 11,800 Answers

In this car the shifting command is electronic, directly controlled by the the TCM - it shifts uncommanded because the power supply from the battery to the transmission computer fluctuates wildly and the computer malfunctions .
Since this happens only at startup it means that the battery can't deliver enough voltage during startup - measure it to see its status, it might be old and in need of a replacement. After that check the connectors in the wiring to the TCM and at the battery, they might be loose or corroded.

Posted on Apr 03, 2011

  • Azrael SRL Apr 06, 2011

    This is in the wiring that goes from the TCM to the gearbox. But since this happens exactly when you put the contact you should verify it - the contacts inside it might be iffy. Since they cannot be fixed you will have to replace the entire key hub.

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2002 ford ranger - Where is the 4x4 actuator located


On the transfer case
Transfer Case - Electronic Shift
The four-wheel drive electronic shift-on-the-fly feature electrically shifts the vehicle transfer case between 2WD, 4WD HIGH, and 4WD LOW. The system mode is selected by the operator through the mode select switch (MSS) on the instrument panel. The operator is informed which mode the system is in by two instrument cluster indicators: one for 4WD HIGH which appears as 4WD, and one for 4WD LOW, which appears as 4WD LOW. Shifts into 4WD HIGH can be made at any speed. When shifting into 4WD HIGH with the vehicle stationary, tooth blockage may occur preventing shift completion. When the vehicle is driven above 8 km/h (5 mph) the shift will complete. When shifting in or out of 4WD LOW, the four-wheel drive (4WD) control module requires that the vehicle speed be less than 5 km/h (3 mph), the brake pedal be applied, and the transmission be in NEUTRAL (automatic transmission) or the clutch pedal be depressed (manual transmission).
The gearmotor encoder assembly is mounted externally on the transfer case. It drives a rotary cam which moves the mode fork and range fork within the transfer case between the 4WD HIGH, 4WD LOW, and 2WD range positions.
The four-wheel drive (4WD) control module controls the gearmotor encoder assembly that shifts between 4WD HIGH, 4WD LOW, and 2WD modes.

Mar 17, 2017 | Ford Cars & Trucks

1 Answer

2OO9SIVERADO 1500W/T 4X4 WHY DONT FRONT HUBS ENGAGE


Automatic transmission or manual ? Which Transfer case does it have ?
Transfer Case - BW 4485-NR3
Transfer Case - MP 1222/1225/1226-NQG
Transfer Case - MP 1625/1626-NQF
Transfer Case - MP 3023/3024-NQH

Do you hear the transfer case lock the axles in ?
The Magna Powertrain (MP) 1625/1626 RPO NQF transfer case features a 3 mode shift control switch located on the instrument panel.

The Magna Powertrain (MP) 1222/1225/1226, RPO NQG transfer case is a 2-speed, part-time with mode shift-on-the-fly capability

Circuit/System Verification
Place the vehicle in 4WD install a scan tool and using engine data 2 look at the display for 4WD signal.
Verify that the scan tool indicates that the vehicle is in 4WD.
? If the scan tool indicates that the vehicle is in 2WD go to circuit system testing.

Your best bet , take your vehicle to a qualified repair shop !

Jan 31, 2017 | Cars & Trucks

1 Answer

I recently purchased a 1999 Chevy Blazer 4WD LT with the 4WD AUTO 4 switch push button. We picked it up cheap. We now know why... 4WD dash switch is dead, changed it with a used one lights flash and n


Sounds like the encoder switch is bad ..it on the transfer case .it has a motor with wires going to it.when you press the button it sends a signal to that motor to switch into a certain gear..

Apr 21, 2012 | Cars & Trucks

1 Answer

4wd/4low lights flash


Hi there:
That flashing is a signal from the GEM computer that indicates a failure in the Control-Trac system. Typically it is one of the Hall-effect axle speed sensors (located in the t-case) that has failed. In the auto position on your model the system monitors relative front and rear axle speeds, increasing the period of engagement of the clutch pack in the transfer case to eliminate the rear moving faster than the front. If it gets to full-lock, for example, and the rear still seems to be turning faster then it reverts the system to 4WD (locks the transfer case in 4wd as it does in 4wd-lo) and flashes the lights to tell you of the problem (in 97 and later models it reverts to 2WD in the default, auto position). Some have reported cleaning the contacts on the speed sensors has helped, but you may want to get to a dealer if the problem persists. Watch that they dont automatically try to replace the computer or the transfer case. Usually it is just a sensor problem, which is relatively easy and inexpensive to replace. There is a shift motor on the t-case on these models, but it is only used to select 4wd-lo and yours seems to do that OK.

Other details HERE.

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Feb 23, 2012 | 1997 Ford Explorer AWD

1 Answer

4wd 4wdlow light flashing


Hi there:
That flashing is a signal from the GEM computer that indicates a failure in the Control-Trac system. Typically it is one of the Hall-effect axle speed sensors (located in the t-case) that has failed. In the auto position on your model the system monitors relative front and rear axle speeds, increasing the period of engagement of the clutch pack in the transfer case to eliminate the rear moving faster than the front. If it gets to full-lock, for example, and the rear still seems to be turning faster then it reverts the system to 4WD (locks the transfer case in 4wd as it does in 4wd-lo) and flashes the lights to tell you of the problem (in 97 and later models it reverts to 2WD in the default, auto position). Some have reported cleaning the contacts on the speed sensors has helped, but you may want to get to a dealer if the problem persists. Watch that they dont automatically try to replace the computer or the transfer case. Usually it is just a sensor problem, which is relatively easy and inexpensive to replace. There is a shift motor on the t-case on these models, but it is only used to select 4wd-lo and yours seems to do that OK.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Feb 23, 2012 | Ford Explorer Cars & Trucks

1 Answer

2003 F-150 regular cab automatic transmission and the 4WD will not engage.


Operationally vacuum shifts the front axle between 2WD and 4WD mode. The GEM ( Generic Electronics Module ) applies ground to the solenoid needed for the mode selected on the switch ( for ESOF ) or when the transfer case shift lever is moved ( MSOF ).The contact plates in the transfer case signal the GEM that the transfer case is engaged, and the Vacuum solenoids need to be activated ( either 2WD to 4WD or 4WD to 2WD ).


Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
- If it turns it is a problem with the transfer case.
- If it doesn't it is a front axle engagement problem.

- If the front drive shaft does not turn :
•With the truck running ( with front wheel back on the ground ), switch from 2WD to 4WD and back again, the vacuum shift motor should move the lever on the front axle.
{ picture of shift motor }
-- If the vacuum shift motor does not move:
•Check for vacuum on the lines while shifting between modes. Pink vacuum line is 2WD mode, Light Blue vacuum line is 4WD.
•Check the fuses for the 4WD system and the solenoids.
•Check the vacuum lines from the vacuum shift motor to the solenoids on the firewall.
•Check the vacuum lines from the solenoids to the vacuum reservoir box behind the battery.
•Check the vacuum reservoir box for cracks.
•Typical solution is the vacuum lines ( to the solenoids or to the vacuum shift motor ) are cracked or the vacuum shift motor has a cracked diaphragm and has water in it.
•Could be the shift plate contacts in the transfer case are corroded / not making good contact, and not activating the solenoids.
sscullys_111.jpg

- If the front drive shaft turns:
•For ESOF system
-- Check the fuses for the transfer case, engine compartment fuse panel, 17 & Cab fuse panel fuses 13 and 23 ( verify with owners manual, 97-97 & 99-03 MY can be slightly different on some items ).
-- Try hitting the transfer case with a dead blow hammer ( do not use a metal hammer, it can damage the transfer case ) to see if the transfer case shift motor is hung up .
-- Check the transfer case connector, to make sure the connector pins are clean and making good contact.
•For MSOF systems
-- Check that the shift linkage on the transfer case is moving when the lever is moved from 2W to 4H and 4L.

Jan 10, 2011 | 2003 Ford F150 Regular Cab

2 Answers

My 4x4 is stuck in four wheel low it is shift on the fly and i have already replaced the transfer case motor


Ok here is a long shot but sometimes it will work. Put the 4wd position switch to 4wd Lo, put your transmission in reverse and back up for about 50 yards, stop and put your transmission in neutral, then shift the 4wd to 4wd hi, wait a few seconds and shift the 4wd to 2wd hi, Sometimes the t-case will get stuck and this is how you reset the computer. I have known people that really got their t-cases messed up because they thought that shift on the go meant that they could shift the t-case into 4wd LO while moving but shift on the go is only for 4wd hi the gears will not mesh up fast enough for 4wd LO because the ratio is 1 to 1 . I hope this helps you.

Feb 08, 2010 | 1990 Ford Bronco

1 Answer

1997 Suburban Transfer Case stuck in 4WD Lo


most likely needs an encoder motor. That is the fancy term for the motor that switches the t_case through the gears. The flashing lights indicate a code had been stored and you should have gotten it serviced then before further damage. as long as you dont drive it in 4 wheel you should still be ok

May 10, 2009 | 1997 GMC Suburban

2 Answers

Stuck in Lo Range 4WD. Suggestions?


Try key in run position(without starting it) and try to shift it into 4wd high with the shift lever in neutral.

Apr 26, 2009 | Chevrolet Suburban 1500 Cars & Trucks

1 Answer

4WD


Look for damaged wires, or something bent, on the Auto Disconnect Device on the front axle before you do anything else. The 4WD HI light is not coming on because the front diff is not engaging.
Re 4 LO: In 4 LO, you ar NOT getting "4 LO", what you are really getting 2WD LO, because of the output gearing of the transfer case.
In any case, your front diff is not locking in, in either mode. The A.D.D. controls the 4 Hi lite.

Oct 11, 2008 | 1997 Toyota 4Runner

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