TRANSFER CASE SERVICE - 1997 Ford Expedition

Which of these does your vehicle have
Transfer Case - NVG 126-NP4
Transfer Case - NVG 226-NP8
Do you know what a RPO code is ? Where it's located on the vehicle ? RPO code NP4 or NP8 will tell you which transfer case your's has . Vacuumn has nothing to do with it . controlled electroniclly . Having a professional scan tool hooked up an DTC'S - diagnostic trouble codes check is what you should do .

The production/process codes provide the description of the Regular Production Options (RPOs) used on the vehicle. The RPO list is printed on the Service Parts Identification Label. The following is a list of the RPO abbreviations and the description of each:
NP4
Transfer Case Active Single Speed All Wheel Drive (AWD)
NP5
Steering Wheel Leather Wrapped
NP7
Steer Column EEC Approved
NP8
Transfer Case Active All Wheel Drive (AWD) 2 Speed

SERVICE 4WD indicator
The SERVICE 4WD indicator is an integral part of the cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle that a transfer case system malfunction. The SERVICE 4WD indicator is controlled by the transfer case shift control module via Class 2.

Which transfer case does it have ????

Is the service light on ?
SERVICE indicator (4WD/AWD) Lamp
The SERVICE indicator (4WD/AWD) lamp is an integral part of the cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle of malfunctions within the automatic transfer case (ATC) system. The SERVICE indicator (4WD/AWD) lamp is controlled by the transfer case shift control module via CKT 1567.
Circuit Description
The ignition switch supplies Ignition 3 voltage to the transfer case shift control module at connector C1 terminal E10 using the 4WD Fuse. When the ignition switch is first turned to the RUN position, the transfer case shift control module responds by flashing the SERVICE indicator (AWD/4WD) lamp for approximately 2 seconds, then turning it OFF, while performing tests on the ATC system. The transfer case shift control module will continue to perform tests on the ATC system during a normal drive cycle.

Hooking up a factory or some other professional scan tool that can view DTC'S - diagnostic trouble code's in the 4X4 control module would be the best way to find the problem.

DTC B0768 Service Indicator Circuit High
DTC B2725 ATC Mode Switch Circuit Malfunction
DTC C0300 Rear Speed Sensor Malfunction
DTC C0305 Front Speed Sensor Malfunction
DTC C0308 Motor A/B Circuit Low
DTC C0309 Motor A/B Circuit High
DTC C0310 Motor A/B Circuit Open
DTC C0315 Motor Ground Circuit Open
DTC C0323 T-Case Lock Circuit Low
DTC C0324 T-Case Lock Circuit High
DTC C0327 Encoder Circuit Malfunction
DTC C0357 Park Switch Circuit High
DTC C0362 4LO Discrete Output Circuit High
DTC C0367 Front Axle Control Circuit High
DTC C0374 General System Malfunction
DTC C0376 Front/Rear Shaft Speed Mismatch
DTC C0387 Unable to Perform Shift

There are three different transfer case's ! Which of these does your olds have ?

Transfer Case - NVG 136-NP4 (One Speed Automatic)
Transfer Case - NVG 233-NP1 (Two Speed Selectable)
Transfer Case - NVG 236 (Two Speed Automatic)

All three have an electronic control module ! When the light is on DTC'S are stored in the transfer case shift control module .

SERVICE indicator (AWD/4WD) lamp
The SERVICE indicator (AWD/4WD) lamp is an integral part of the instrument cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle of malfunctions within the automatic transfer case (ATC) system. The SERVICE indicator (AWD/4WD) lamp is controlled by the transfer case shift control module via a Class 2 serial data message.

There are three speed sensors on the Automatic Transfer Case (ATC), two on the rear output shaft and one on the front output shaft. Each speed sensor is a Permanent Magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases as speed increases.
Vehicle Speed Sensor
One of the two speed sensors on the rear output shaft is the vehicle speed sensor (VSS). It is an input to the vehicle control module (VCM). The VCM sends this information to the transfer case shift control module via the Class 2 Serial Data bus.
Rear Propshaft Speed Sensor
The transfer case shift control module converts the pulsating AC voltage from the rear propshaft speed sensor to a Rear Propshaft Speed in RPMs to be used for calculations. The Rear Propshaft Speed can be displayed with a scan tool.
Front Propshaft Speed Sensor
The transfer case shift control module converts the pulsating AC voltage from the front propshaft speed sensor to Front Propshaft Speed in RPM to be used for calculations, and to monitor the difference between the front and rear propshaft sensor speed. It is also used in the AUTO 4WD mode of operation to determine the amount of slip and the percent of torque to apply to the front axle. The Front Propshaft Speed can be displayed with a scan tool.

Transfer Case Encoder Motor
The transfer case encoder motor is a permanent magnet D.C. motor and gear reduction assembly. The encoder motor is controlled with a Pulse Width Modulated (PWM) signal provided by the transfer case shift control module. It is located on the left hand side (drivers side) of the transfer case. When activated it turns the sector shaft of the transfer case to shift the transfer case. This circuit consists of a power supply relay (Motor Feed A circuit ) that supplies voltage to the motor. The Motor Control B circuit is a PWM driver that varies the duty cycle to control the amount of current through the motor to ground.

There are a number of codes that can set .
DTC C0300 Rear Speed Sensor Malfunction
DTC C0305 Front Speed Sensor Malfunction
DTC C0308 Motor A/B Circuit Low
DTC C0309 Motor A/B Circuit High
DTC C0310 Motor A/B Circuit Open
DTC C0315 Motor Ground Circuit Open
DTC C0374 General System Malfunction
DTC C0376 Front/Rear Shaft Speed Mismatch
DTC C0550 ECU Malfunction
DTC C0611 VIN Information Error

You don't want to just start replacing parts , that could cost $$$$$$ . You could check connections at all the sensors an the control module , but other then that ,well . Your best bet , take it to a qualified repair shop .

Need to have it check for DTC'S - diagnostic trouble codes , see if a scan tool will communicate with it , see if it will show data PID'S .
SERVICE indicator (4WD/AWD) Lamp
The SERVICE indicator (4WD/AWD) lamp is an integral part of the cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle of malfunctions within the automatic transfer case (ATC) system. The SERVICE indicator (4WD/AWD) lamp is controlled by the transfer case shift control module via CKT 1567.

Is your service indicator lamp lit ?
which of these does your jimmy have
Transfer Case - NVG 233-NP1 (Two Speed Selectable)
Transfer Case - NVG 236 (Two Speed Automatic)

Which transfer case does your truck have ?
SERVICE 4WD
Refer to
?€¢
Transfer Case Description and Operation for the Transfer Case - NVG 149-NP3

?€¢
Transfer Case Description and Operation for the Transfer Case - NVG 246-NP8

?€¢
Transfer Case Description and Operation for the Transfer Case - NVG 261-NP2

?€¢
Transfer Case Description and Operation for the Transfer Case - NVG 263-NP1

The SERVICE 4WD indicator is located in the instrument panel cluster (IPC), and shares the common power and ground of the IPC. The transfer case shift control module controls the service indicator by sending the IPC a Class 2 message. This indicator may be controlled with the scan tool using the IPC device controls.
You should take it to the dealer an have it checked for DTC'S -diagnostic trouble codes

You need to check wiring an connectors at the transfer case shift control module an check power an grounds at the module ! If all seams good there a scan tool will need to be hooked up to check for codes ! If none of this makes no sense or you don't under stand any of this you need to take it to someone who does !

1

Was the Transfer Case Diagnostic System Check performed?
--
Go to Step 2
Go to Transfer Case Diagnostic System Check

2

1. Install the Scan Tool .
2. Turn the ignition ON, engine OFF.
3. Use a Scan Tool in order to command the SERVICE indicator (AWD/4WD) lamp OFF.

Does the SERVICE indicator (AWD/4WD) lamp turn off?
--
Go to Step 3
Go to Step 4

3

Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement .
Is the repair complete?
--
Go to Transfer Case Diagnostic System Check
--

4

Replace the instrument cluster. Refer to Instrument Cluster Replacement in Instrument Panel.
Is the repair complete?
--
Go to Step 5

I guess you probably don't know what transfer case you have ?
SERVICE 4WD
Refer to
?€¢
Transfer Case Description and Operation in Transfer Case - NVG 149-NP3

?€¢
Transfer Case Description and Operation in Transfer Case - NVG 246-NP8

?€¢
Transfer Case Description and Operation in Transfer Case - NVG 261-NP2

?€¢
Transfer Case Description and Operation in Transfer Case - NVG 263-NP1

The NVG 246 EAU provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and Neutral.
The four manual mode, or range gear positions, of the NVG 261 transfer case are:
?€¢
2HI - 2 wheel drive high range

?€¢
4HI - 4 wheel drive high range, part-time

?€¢
4LO - 4 wheel drive low range, 2.72:1 gear ratio reduction

?€¢
N - Neutral, 4 wheel

The NVG 263 transfer case provides the driver with 4 manual mode/gear positions:
?€¢
2HI - 2 Wheel Drive high range

?€¢
4HI - 4 Wheel Drive high range

?€¢
4LO - 4 Wheel Drive low range

?€¢
Neutral

With the info I've given you ,you should be able too now !
There is probably a code stored somewhere !
DTC B0790 DTC B2725 DTC C0300 DTC C0305 DTC C0306 DTC C0321 DTC C0327 DTC C0359 DTC C0374 DTC C0379 DTC C0550.

The service 4x4 light coming on indicates problem with the system an DTC'S - diagnostic trouble codes are stored . Before replacing parts have a qualified repair shop do diagnostic's . ! Guessing an replacing parts on electronically controlled systems never fixes cars.
Do you know what DTC'S are ?
DTC B0775
DTC B0780
DTC B0785
DTC B0790
DTC B2725
DTC C0306
DTC C0379
DTC C0387
DTC C0396
DTC C0550
DTC C0569
DTC C0896
DTC P2160 or P2161
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-NQH
Transfer Case - NVG 261-NP2

You definitely need to have it serviced & checked out...The service 4WD indicator read across my screen, but I did not have serviced...Eventually, I heard a grinding noise & because I didn't have it serviced when I took it in, it was found that the transfer case had no tranfer case fluid at all...This damaged the transfer case which had to be replaced (used transfer case-$400.00)....The transfer case is part of your transmission...The shape mine was in could have broke my transmission...Have it taken care off before it gets too bad...You must use only GMC Transfer Case Fluid

How may buttons for the 4X4 two , three , or four ? Do the lights flash ? Any messages - service four wheel drive system ? Which transfer case does it have ?

Transfer Case - NVG 246-NP8 (Two Speed Automatic)
The transfer case shift control module uses the VIN information for calculations that are required for the different calibrations used based on axle ratio, transmission, tire size, and engine. The system does not know which calibration to use without this information.
Transfer Case Encoder Motor
The transfer case encoder motor consists of a permanent magnet (PM) DC motor and gear reduction assembly. It is located on the left hand side (drivers side) of the transfer case. When activated it turns the sector shaft of the transfer case (clockwise or counter clockwise) to shift the transfer case. The encoder motor is controlled with a pulse width modulated (PWM) circuit within the transfer case shift control module. This circuit consists of a driver on both the Motor Feed A and Motor Feed B circuits. The encoder motor is bi-directional to allow the motor to shift the transfer case from 2HI or 4HI to NEUTRAL and 4LO positions.
Transfer Case Encoder
The encoder is mounted to the transfer case encoder motor assembly and is replaced as an assembly. The encoder converts the sector shaft position (representing a mode or range) into electrical signals inputs to the transfer case shift control module. The module can detect what position the transfer case is in by monitoring the 4 encoder channels (P, A, B, and C). These inputs translates into AUTO 4WD, 2H, 4H, NEUTRAL, and 4L or in transition between gears.
Transfer Case Motor Lock
The transfer case motor lock is used to provide a 2H, 4H, and 4L lock-up feature. When the lock circuit is energized, the transfer case encoder motor is allowed to turn. When the transfer case is placed 2H, 4H, or 4L the motor lock circuit has no power provided to it and the lock is applied. This assures that the transfer case remains in the current gear position. When AUTO 4WD is selected the motor lock remains applied until an adaptive mode (torque is applied to the front propshaft) is required. During an adaptive mode the motor lock circuit is energized and the motor lock is released, enabling the encoder motor to turn and apply torque to the front propshaft.


SERVICE indicator (4WD/AWD) Lamp
The SERVICE indicator (4WD/AWD) lamp is an integral part of the cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle of malfunctions within the automatic transfer case (ATC) system. The SERVICE indicator (4WD/AWD) lamp is controlled by the transfer case shift control module via a Class 2 message or by a Sevice Indicator Control Circuit.

The first thing to do before assuming it's a loose wire would be to have it checked for codes , auto zone , advance etc... can not check this codes .
DTC B0768 Service Indicator Circuit High
DTC B2725 ATC Mode Switch Circuit Malfunction
DTC C0300 Rear Speed Sensor Malfunction
DTC C0305 Front Speed Sensor Malfunction
DTC C0308 Motor A/B Circuit Low
DTC C0309 Motor A/B Circuit High
DTC C0310 Motor A/B Circuit Open
DTC C0315 Motor Ground Circuit Open
DTC C0323 T-Case Lock Circuit Low
DTC C0324 T-Case Lock Circuit High
DTC C0327 Encoder Circuit Malfunction
DTC C0357 Park Switch Circuit High
DTC C0362 4LO Discrete Output Circuit High
DTC C0367 Front Axle Control Circuit High
DTC C0374 General System Malfunction
DTC C0376 Front/Rear Shaft Speed Mismatch
DTC C0387 Unable to Perform Shift
DTC C0550 ECU Malfunction
DTC C0611 VIN Information Error

If you know nothing about this , your best bet would be to take it to a qualified repair shop .