Question about 2002 Chevrolet TrailBlazer

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Transmission shifting into various 4wd modes on its on

Shifting while car is still in motion

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It is most likely the sensor attached to the 4wd motor that tells the computer what position the motor is in. The easiest thing you can try on your own is to dis-connect the neg term on your battery, wait a few mins and re-connect the battery. This re-boot procedure may fix it permanently, temporarily or not at all but its worth a shot since it wont cost you a cent.
Mike in Hawley,PA

Posted on Feb 15, 2009

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How do I repair the four wheel drive on a 1999 Ford Ranger XLT?


It depends on what is wrong , is the 4x4 light flashing ? Are you aware of the complexity of the 4x4 system ? Has a electronic control module , has the ability to set an store DTC'S - diagnostic trouble codes !
Transfer Case The four wheel drive system is an electronic shift 4X4 system that allows the operator to choose between three different modes. The operator can switch 4X4 HIGH modes at any speed. To engage or disengage 4X4 LOW the vehicle speed must be less than 5 kph (3 mph), the brake depressed, and the transmission must be in NEUTRAL.
The shift motor sense plate, an integral part of the electronic shift motor, informs the generic electronic module (GEM) of the transfer case shift motor and contact plates A, B, C and D position.
The digital transmission range (TR) sensor is located on the LH side of the transmission, and informs the GEM when the transmission is in the NEUTRAL position.
The electronic shift motor is mounted externally at the rear of the transfer case. It drives a rotary cam which moves the mode fork and range fork within the transfer case between the 4X4 HIGH, 4X4 LOW and 2WD range positions.
When the GEM verifies the completion of the transfer case shift from 2WD to 4X4 HIGH (reading the contact plate positions), the GEM will then energize both pulse vacuum hublock (PVH) solenoids (supplying ground for 45 seconds). The PVH solenoid will allow a HIGH flow of intake manifold vacuum to the "wheel end hublocks", engaging the wheel end hubs to the front differential and transfer case to achieve four wheel drive.
Here are just a few DTC'S the system can set an store in the module !
P1804 4WD High Indicator Circuit Failure GEM GO to Pinpoint Test C . P1806 4WD High Indicator Short to Battery GEM GO to Pinpoint Test C . P1808 4WD Low Indicator Circuit Failure GEM GO to Pinpoint Test C . P1810 4WD Low Indicator Short to Power GEM GO to Pinpoint Test C . P1812 4WD Mode Select Switch Circuit Failure GEM GO to Pinpoint Test A . P1815 4WD Mode Select Switch Circuit Short to Ground GEM GO to Pinpoint Test A . P1820 Transfer Case CW Shift Relay Circuit - Failure GEM GO to Pinpoint Test A . P1822 Transfer Case CW Shift Relay Coil Short to Power GEM GO to Pinpoint Test A . P1824 4WD Electric Clutch Relay Circuit Failure GEM GO to Pinpoint Test A . P1826 4WD Low Clutch Relay Short to Power GEM GO to Pinpoint Test A . P1828 Transfer Case CCW Shift Relay Coil Circuit Failure GEM GO to Pinpoint Test A . P1830 Transfer Case CCW Shift Relay Coil Short to Battery GEM GO to Pinpoint Test A . P1838 Transfer Case Shift Motor Circuit Failure GEM GO to Pinpoint Test A . P1846 Transfer Case CONTACT PLATE "A" Circuit Failure GEM GO to Pinpoint Test A . Now are you sure you really want to mess with this ? You would need a factory diagnostic scan tool to check this out before you start replacing parts !
Here

May 30, 2015 | Ford Ranger Cars & Trucks

1 Answer

Which fuse is the one for the 4/4 switch on the 2001 ranger xlt


All fuses supply power to the four wheel drive control module , the control module supplies power to mode select switch . The 4WD control module accomplishes shifts by interpreting inputs from the following:
  • mode select switch (MSS)
  • vehicle speed signal
  • encoder plate position
  • brake pedal switch
  • digital transmission range (TR) sensor
  • ignition switch
  • transfer case shift motor
  • Based on these inputs, the 4WD control module controls the shifts into 2WD, 4WD HIGH or 4WD LOW with the following outputs:
    • shift motor (clockwise)
    • shift motor (counterclockwise)
  • Fuses
  • Battery junction box (BJB) fuse:
    • 1 (50A)
    • 3 (50A)
    • 13 (20A)
    • 30 (10A)
  • Central junction box (CJB) fuse:
    • 28 (7.5A) (manual transmission)
    • 10 (7.5A)
    • 11 (7.5A)
    • 5 (15A)
    • If the concern remains after the inspection, connect the diagnostic tool to the data link connector (DLC) located beneath the instrument panel and select the vehicle to be tested from the diagnostic tool menu.

Jan 02, 2015 | Cars & Trucks

1 Answer

2005 blazer won't shift out of 4WD


put in reverse get going 5-10 mph put in neutral then try to get out of FWD while still in motion.This doesn't always work but it eliminates
a lot of possibilities.

Mar 10, 2013 | Cars & Trucks

1 Answer

What does this shifting means..3,2,1 on automatic transmission range rover 2.5. Can you still shift the gear from D to 3 while the car is in motion...?


Yes, you can shift while the car is in motion. It works in a similar manner as a manual transmission, except that there is no clutch. Your car has 4 gears + overdrive. 1, 2, 3, 4=D, 5= Overdrive. So if you're on the highway and you shift into 3rd, you're down-shifting twice (from 5th to 3rd). The car will downshift itself if you hit the gas hard enough though! So, yes, you can shift from D to 3 while the car is in motion. No problem. Alex

May 31, 2011 | Land Rover Range Rover Cars & Trucks

1 Answer

How do you use the the four wheel drive gear on a 1998 prado


prado has a fulltime 4wd. you can use the 4wd in any speed but preferrably stop before the shifting to the 4wd mode. if you are using an automatic transmission, put it to neutral before changing the 4wd mode. each mode depends on the surface you are travelling. on pavement the 4 low setting is an advantage for drivers who need to tow and maneuver a heavy trailer. select 4WD high on snow and for easy to moderate off-road (dirt roads, easy trails).


Feb 20, 2010 | 2000 Toyota Land Cruiser

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

2 Answers

4wd does not work


Electronic Shift On the Fly (ESOF) Operation
The ESOF system is an electronic shift 4x4 system that allows the operator to choose between two different 4x4 modes as well as 2-wheel drive. The operator can switch between 2WD and 4WD HIGH mode at speed. To engage or disengage LOW Range, the vehicle speed must be less than 5 kph, the brake depressed, and the transmission must be in NEUTRAL.

The transfer case is equipped with an electromagnetic clutch which is located inside the case. This clutch is used to spin up the front drive-line when shifting from 2WD to 4x4 High mode at speed. When the control switch on the instrument panel is turned, the generic electronic module (GEM) recognizes that a shift has been requested and activates the electromagnetic clutch and the relays which power the transfer case shift motor. When the shift motor reaches the desired position as determined by the contact plate position inputs to the GEM, power to the shift relays and motors will be removed. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the main-shaft hub to the drive sprocket. Finally, the front axle collar is engaged and the electromagnetic clutch is deactivated.

Shift Between 2WD and 4x4 HIGH:
Shifts between 2WD and 4x4 HIGH can be made at speed. Listed below are the inputs and outputs needed by the GEM to execute a change between any of these modes.

Feature Inputs:
*4WD Mode Switch (Various resistances).
*Contact Plate Position Inputs A, B, C, D (grounded when closed, open circuit when open).

Feature Outputs:
*4x4 Shift Motor Relay Outputs
*Transfer Case Clutch Relay (grounded when relay is on, open circuit when relay is off).
*4x2/4x4 Vacuum Solenoid (grounded when activated, open circuit when deactivated).
*Cluster Indicators (ground when activated, open circuit when deactivated).

Shifting Into/Out of 4WD LOW:
When shifting into or out of 4WD LOW, the GEM requires that the vehicle speed be less than 5 kph, the brake is applied, and the transmission is in NEUTRAL.

Feature Inputs:
*4WD Mode Switch (Various resistances).
*Contact Plate Position Inputs A, B, C, D (grounded when closed, open circuit when open).
*VSS Sensor (Sinusoid Signal: 0.7V-20V, 2.2 Hz/mph).
Brake Input (battery voltage when brake is depress, open circuit when not activated).
*Transmission Range Sensor (grounded when transmission is in NEUTRAL, open circuit otherwise).
8Start/Clutch Depressed Input

Feature Outputs:
*4x4 Shift Motor Relay Outputs
*4x2/4x4 Vacuum Solenoid (grounded when activated, open circuit when deactivated).
*Cluster Indicators (grounded when activated, open circuit when deactivated).

4WD Mode Switch
A rotary switch allows the vehicle operator to choose between 2WD, 4WD HIGH, and 4WD LOW modes of 4x4 operation.

GEM Module
The Generic Electronic Module (GEM) controls the operation of the 4x4 system

Vehicle Speed Sensor
The vehicle speed sensor (VSS), mounted in the rear of the transfer case, informs the GEM of the vehicle speed.

Transfer Case Shift Motor Sense Plates

The shift motor sense plate, an integral part of the electric shift motor, informs the GEM to the positions of the transfer case

Transmission Range Sensor
Located on the left side of the transmission, this sensor informs the GEM when the transmission is in the NEUTRAL position.

Electric Shift Motor
The electric shift motor, mounted externally at the rear of the transfer case, drives a rotary cam which moves the mode fork and range fork within the transfer case to select between the 2WD, 4WD HIGH, and 4WD LOW positions.

4x4/4x2 Vacuum Solenoids
These two solenoids are attached to the upper RH side of the engine compartment dash, and alternately route vacuum to the vacuum motor which engages/disengages the center axle disconnect collar in the front axle assembly.

4x4 Shift Motor Relay
A module containing two relays which under the control of the GEM, shift the transfer case shift motor between the 2WD, 4WD HIGH, and 4WD LOW modes.

Transfer Case Clutch Relay
An electromechanical relay is used to activate the transfer case clutch within the transfer case.

Good luck and hope this helps,but start with the simple and check the fuses and wire harness. Both white/light blue stripe wires should have 12V in run. The GEM will ground the left side (closest to engine) solenoid to disengage the front axle. It will ground the the right side solenoid (closest to fender) to engage the front axle. If the GEM doesn't see Neutral it will not let the truck come out of 4Lo. If the GEM had water leaking on it it may well be the root of the problem. The shift motor only has power when the GEM sends it a signal to move the shift lever. Once the shift is completed the motor shuts off. There are 2 wires that control the shift motor. A yellow and an orange. The GEM alternates between 12v and Ground to these wires to control which way the motor turns. The GEM uses the transfer case shift relay module to control the power to the motor. There are contact plates inside the shift motor assembly that indicate the position that the shift lever is in. This is what the GEM used to know what the T-case is doing. Any one of these components can fail.







Jan 10, 2010 | 2002 Ford Explorer

1 Answer

1996 ford explorer 4wheel drive will not engage into the hubs need to know how it works


make sure your 4WD switch is working.and fuse is okay.because your 4WD is control by 4 electric shift motors in which drive a rotary cam which moves the mode fork and range fork inside the transfer case to select between 2WD HIGH A4WD - 4WD HIGH AND 4WD LOW RANGE.a shift motor sensing plate on the shift motor monitors the range in which the transfer case is operating a transmission range sensor monitors the gear position of the transmission.which must be in neutral to shift into low.a pair of solenoids one for 2WD one for 4WD.mounted on the upper right firewall route vacuum to the vacuum motor which engages and disengages the center axle disconnect collar in the front axle assembly.a 4 x 4 shift motor relay module contains two GEM controlled relays which shift the transfer case shift motor between 2WD and 4WD modes.a solid state clutch relay activates the A4WDclutch inside the transfer case.

Dec 13, 2009 | 1996 Ford Explorer

1 Answer

Slower engine speed in 4wd mode, 1st or 2nd gear (auto trans)


mcdevito75 here, I would figure yes, if your shifting while in motion, definetly yes, when you shift your changeing gear ratios in the 4 wheel drive or the transmission, this will cause the engine to slow but also make the gas pedal moe responsive.If you feel or hear this slowing down of the engine while standing still (at a red light) it"s most likely the computer contolled sensor in the tranny. I woulkd still check with my local shop for their advice too.

Nov 25, 2009 | 2004 Ford F150

1 Answer

Transmission shifting into various 4wd modes on its own


I had a similar problem with my van. The transmission randomly selected gears. It was the PRNDL1 switch..This switch is controlled by the gear shift lever. I had a shop replace the switch for me, so I don't know where it is located. Hope this helps

Feb 06, 2009 | 2002 Chevrolet TrailBlazer

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