Possible Causes

WARNING: This page is about a different car, the 2005 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.

high speed CAN circuits (W) and (B) shorted to ground or open
DLC D-01
0318-01
4WD control module

FOUR-WHEEL DRIVE (4WD) CONTROL MODULE DOES NOT RESPOND TO DIAGNOSTIC TOOL - DIAGNOSTIC PROCEDURE

PINPOINT TEST 4		THE FOUR-WHEEL DRIVE (4WD) CONTROL MODULE DOES NOT RESPOND TO THE DIAGNOSTIC TOOL
STEP	INSPECTION		ACTION
1	CHECK THE HIGH SPEED CAN CIRCUITS BETWEEN THE 4WD CONTROL MODULE AND THE DLC FOR AN OPEN Key OFF. Disconnect the 4WD Control Module 0318-01. Measure the resistance between the 4WD control module 0318-01 pin 5, circuit (W), harness side and the DLC D-01 pin 6, circuit (W), harness side; and between the 4WD control module 0318-01 pin 13, circuit (B), harness side and the DLC D-01 pin 14, circuit (B), harness side. Are the resistances less than 5 ohms?	Yes	GO to next step.
1		No	REPAIR the circuit in question. CLEAR the DTCs. REPEAT the self-test. CARRY OUT the data link diagnostics test.
2	CHECK FOR CORRECT 4WD CONTROL MODULE OPERATION Disconnect all the 4WD control module connectors. Check for: corrosion pushed-out pins Connect all the 4WD control module connectors and make sure they seat correctly. Operate the system and verify the concern is still present. Is the concern still present?	Yes	DIAGNOSE the high speed CAN. See PINPOINT TEST 8: NO MODULE/NETWORK COMMUNICATION - NO POWER TO THE DIAGNOSTIC TOOL .
2		No	The system is operating correctly at this time. Concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test. CARRY OUT the data link diagnostics test.
Courtesy of MAZDA MOTORS CORP.
Courtesy of MAZDA MOTORS CORP.