OVERALL SYSTEM CHECK 1. Raise vehicle off ground and support with jackstands, so all 4 wheels can rotate. Start engine and place transfer case shift lever in "L" position on Land Cruiser, "L4" position on Tacoma, and 4WD position on 4Runner. On Land Cruiser, turn differential lock control switch to "RR", on all other models turn differential lock control switch on. Ensure indicator light turns on. Go to next step. 2. If light indicator light is blinking, rotate tires to engage differential gears. Turn differential lock control switch off, and ensure indicator light turns off. Go to next step. 3. Turn differential lock control switch on. Locate 4WD control unit. See Fig. 1, Fig. 2 or Fig. 3. With wheels turning at 5 MPH, measure voltage between 4WD control unit terminals No. 2 and 3 by backprobing connector. See Fig. 4. Voltage should be 0.5 volt or less. If voltage is not as specified, check wiring harness for short to voltage. See WIRING DIAGRAMS. Repair as necessary. Turn differential lock control switch off. Stop engine and lower vehicle. Fig. 4: Identifying 4WD Control Unit Terminals Courtesy of TOYOTA MOTOR SALES, U.S.A, INC.
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DIFFERENTIAL LOCK CIRCUIT 1. Ensure battery voltage is 10-14 volts. Disconnect 4WD control unit connector. Turn ignition on and go to next step. 2. Check differential lock actuator circuit. Using ohmmeter, measure resistance between 4WD control unit wiring harness connector terminals No. 2 and 3. See Fig. 5. Resistance should be less than 100 ohms. If resistance is as specified, go to next step. If resistance is not as specified, go to step 9. 3. Check ground circuit. Check continuity between 4WD control unit wiring harness connector terminal No. 7 and ground. Continuity should exist. If continuity is as specified, go to next step. If continuity is not as specified, go to step 9. 4. Check vehicle speed sensor circuit. Check continuity between 4WD control unit wiring harness connector terminal No. 10 and ground. Move vehicle slowly (at least 5 MPH). A pulse of continuity should exist for each 15.8" (401 mm) of movement. If continuity is as specified, go to next step. If continuity is not as specified, go to step 9. 5. Check DIFF fuse circuit. Measure voltage between 4WD control unit wiring harness connector terminal No. 5 and ground. If battery voltage is not present, check and replace fuse as necessary. If fuse is okay, go to step 9. If battery voltage is present, go to next step. 6. Check differential lock position switch circuit. Measure voltage between 4WD control unit wiring harness connector terminal No. 1 and ground. When differential lock indicator light is on, no voltage should be present. When differential lock indicator light is off, 10-14 volts should be present. If voltage is as specified, go to next step. If voltage is not as specified, go to step 9. 7. Check 4WD position switch circuit. Measure voltage between 4WD control unit wiring harness connector terminal No. 8 and ground. With 4WD shift lever in "N" or "H" position, no voltage should be present. With shift lever in "L" position on Land Cruiser, "L4" on Tacoma, and 4WD on 4Runner, voltage should be 10-14 volts. If voltage is as specified, go to next step. If voltage is not as specified, go to step 9. 8. Check differential lock control switch circuit. Measure voltage between 4WD control unit wiring harness connector terminal No. 4 and ground. With control switch off, no voltage should be present. With control switch on, 10-14 volts should be present. If voltage is as specified, go to step 10. If voltage is not as specified, go to next step. 9. Check components and wiring harness. Check appropriate component (if necessary). See COMPONENT TESTS. Replace as necessary. If appropriate component is okay, check harness and connectors for terminal damage, corrosion or pins pushed out. Repair or replace as necessary and retest system. 10. Check circuit with control unit connected. Turn ignition off. Connect 4WD control unit connector. Turn ignition on. With differential control switch in specified positions, check voltage at 4WD control unit by backprobing connector.
Saturday, November 23rd, 2019 AT 5:50 PM
(Merged)