The 1995 & up Ford Ranger 4x4's with the electric shift transfer case uses a 4WD control module. The 1995-2000 Rangers have it in the dash. The 2001 and up models have it in the kick panel behind the drivers seat. This system monitors the 4x4 mode select switch and controlled external relays to power up the shift motor to move it into the commanded position. The module relies on four contact plates that are integral to the shift motor to tell it what position the shift motor is in. The system will fail and be unresponsive if the control module does not know the exact position of the shift motor. Usually if it is a contact plate problem, the 4WD module will output code P1867 for contact plate circuit failure.

Normal Operation:

When you turn on the ignition, the 4WD 4HI and 4LO lights should momentarily light up.

With the vehicle on, the 4HI light should come on, you should hear a click and hear the transfer case engage when you set the selector switch to 4HI.

With the vehicle on and in neutral, you should hear the same thing as the transfer case engages 4LO and the 4LO light comes on.

Diagnosing:

NOTE: Before doing anything, check to make sure the fuses for the 4WD system aren't blown. A blown fuse can cause the 4WD lights to flash. There is a fuse in panel in the dash and one in the distribution box under the hood.

The first step in diagnosing the system is to establish communication and retrieve trouble codes from the control module. After retrieving the codes, write them down, clear the codes and retest to see which codes are regenerated. False codes can be set if a component is disconnected when the key is turned on.

If the 4WD lights flash on and off, and no codes are found in the 4WD control module, try clearing the codes anyway. After a certain amount of key cycles, the codes will normally clear from the 4WD control module, but the module will not respond to commands until it is re-initialized by clearing the codes or disconnecting the battery to erase its memory.

If your scan tool will not communicate with the 4WD module, first verify that the scan tool has the proper software and the latest updates. If it does, then try another scan tool. If it still has no communication, the power and grounds that are supplied to the module will need to be tested. See if the scan tool will communicate with the other modules on the shared communication network. If they're OK, check the harness from the data link connector (DLC) for an open circuit to the 4WD module.

There are four contact plate sensors in the shift motor. The 4WD module sends a reference voltage (V-REF) to these contact plates and monitors this voltage. The actual REF voltage will vary depending on the calibration of the module, but the REF voltage should read the same on all contact plates. There is a fifth wire that is a ground. It will ground out the V-REF depending on the position of the shift motor. The contact plate parameter identification descriptions (PIDS) are usually labeled A, B, C and D on the scan tool data. Using this data, the PIDS can be monitored to see if they read correctly. The PIDS will read open or closed and change correctly when the shift motor moves.

If the PID chart is unavailable, monitor the contact plate PIDS and simply unplug the shift motor. When this happens, all four contact plates should read the same, either open or closed.

If the contact plates read correct unplugged but read incorrect with the shift motor plugged in, the shift motor will need to be replaced, as the contact plates are not serviced individually.

If all of the contact plates read the same, each circuit can be tested individually by providing the ground (the common fifth wire) to that contact plate circuit. Monitor your scan tool data and ground each contact plate wire in succession looking for the scan tool data to change from open or closed. The ground is usually identified as "position return" or "encoder ground" on the electrical schematics.

Member Examples:

Forum member 'Rich' experienced problems with the 4WD control module on his 1996 4x4 Ranger. Rich checked for DTC codes and found none. He worked through the series of pinpoint tests. He pulled the radio for access and disconnect and tested the 4WD switch for resistance in each position. He disconnect the GEM in dash and tested several wires for continuity and voltage. He disconnected and tested the transfer case shift control module behind the GEM. The relay module was supposed to show 80-140 ohms between two pins, showed zero. Rich went to the dealership, got a new module, went out to the parking lot and plugged it in, tested the 4LO, and it was fixed.

Rich reports that the 4WD control module is behind the GEM (closer to the firewall) and is much smaller. It's more of a cube, maybe 3 inches on a side. As he recalls, the GEM was mounted just to the left of the radio location, and the 4WD control module was at the same height and within about 6 or 8 inches of the GEM. It only has a few wires running to it.

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