Borg Warner 4405 transfer case

How Borg Warner 4405 transfer case works

The Borg Warner 4405 transfer case was introduced in 1995 and is used by Ford in Explorer and Mercury Mountaineer vehicles. Borg Warner 4405 transfer case is an Automatic Four Wheel Drive system. It’s controlled by the Generic Electronic Module (GEM). When in the automatic mode, the transfer case can vary the torque between the front and rear drive shafts so the vehicle can drive at highway speeds in full time 4WD.

Borg Warner 4405 transfer case

Borg Warner 4405 transfer case in Automatic Mode

The transfer case includes a viscous clutch that is normally applied at a minimum duty cycle which transfer most of the torque to the rear wheels. The viscous clutch is filled with a high viscosity fluid, which flows through slots in the plates. The resistance to shear causes the plates to transmit torque at the needed ratio. The ratio that torque is transmitted at is approximately 35% front and 65% rear. The clutch is a non-repairable item.

The GEM monitors wheel speed differences between the front and rear wheels and increases the duty cycle on the clutch packs to send up to 98% of the torque to the front wheels. When the GEM detects that the front and rear drive shafts speeds are equal, it returns the clutch pack to minimum duty cycle

Borg Warner 4405 transfer case in 4X4 HI

The driver can manually choose to operate the transfer case in 4X4 HI mode by using the dash mounted rotary switch. When set to 4x4HI, the transfer case equally divides the torque 50/50 to the front and rear wheels for driving in snowy or slippery conditions.

The shift to 4x4HI can be made at any time “on the fly”.

Borg Warner 4405 transfer case in 4X4 LO

The driver can also manually operate the transfer case in 4×4 LO mode by using the dash mounted rotary switch. This 4x4LO mode should only be used in low speed situations or off-road conditions. To shift into 4x4LO, the brake must be applied, transmission in neutral and vehicle speed less than 3-MPH.

Borg Warner 4405 transfer case inputs

The GEM module receives inputs from these sensors:

• 4WD Mode Switch

• Vehicle Speed Sensor

• Front and Rear Drive Shaft Speed Sensors

• Transmission Range Sensor

• The brake switch

• Contact Plate 4 position Sensor inside the transfer case electric shift motor.

Borg Warner 4405 transfer case clutch

The transfer case clutch pack receives a pulse width modulated signal from the GEM module and through a solid-state clutch relay. This signal is grounded when the clutch is active and shows battery voltage when off. The A4WD indicator shows the mode chosen. When active, the indicator circuit is grounded.

Borg Warner 4405 transfer case GEM module

The GEM performs self diagnosis and sets trouble codes. It’s important to note that components OUTSIDE of the transfer case system can create conditions that will set codes, so external checks must be made prior to any further diagnosis.

Borg Warner 4405 transfer case and tire pressure

Tire pressure and size can have a substantial effect on the inputs from the drive shaft speed sensors to the GEM. Even a few psi difference in tire pressure or tread wear between the tires can set a trouble code.

So it’s critical to equalize all tire pressures and measure all tire diameters as the first step to diagnosis.

Borg Warner 4405 transfer case fluids

Fluid capacity 1.3 quarts

Fluid type Mercon ATF

Borg Warner 4405 transfer case known failures

Noise

The Borg Warner 4405 transfer case will make noise if there’s a difference in tread depth of more than 0.15mm (0.06-in.) between front and rear wheels. The difference in rolling circumference can be caused by tread wear or tire pressure differences.

The transfer case can also make noise if the unit is low on fluid.

Wheel/Tire bounce, vehicle skip

Again check tread wear difference

Loss of drive

The Borg Warner 4405 transfer case is known to suffer mechanical failure resulting in a loss of drive accompanied by a ratcheting noise coming from the transfer case during coast or deceleration or when in reverse. Prior to the failure, the transfer case likely made an occasional thump noise at a constant road speed of 40-60 MPH. Upon inspection you’ll find the range hub and range fork damaged. Replacing these items will NOT solve the problem.

The range hub is designed with helical cut gearing that stays in mesh under load, but moves out of mesh on coast due to the thrust loads generated by the helical design. Adding power causes the gear to return to the correct position. However, the bottom of the teeth get damaged and the constant pressure on the fork causes it to degrade and burn. The root cause of the problem is an offset in the centerline distance, which places the shift rail at an angle, allowing the range fork to move out of position.

The transfer cases is made from magnesium and rebuilding shop can re-machine the case to correct this design flaw. If you see units with oblong holes in the cases where the shift rail rides. It is cheaper and more efficient to buy a rebuilt unit that has been re-machined than to try and correct this problem yourself.

Borg Warner 4405 transfer case trouble codes

Ford has programmed the GEM module to generate 134 pinpoint tests to track down the electrical glitches.

B1342 ECU Defective

P1804 4WD HIGH Indicator Light Circuit Fault

P1806 4WD HIGH Indicator Light Circuit Short To Voltage

P1808 4WD LOW Indicator Light Circuit Fault

P1810 4WD LOW Indicator Light Circuit Short To Voltage

©, 2018 Rick Muscoplat