Test TG: 4WD Low (4X4L) Range
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2002 Lincoln Navigator, 2002 Ford Expedition, 2001 Lincoln Navigator, 2001 Ford RV Cutaway, and 2001 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
After each service or repair procedure has been completed, reconnect all components. Clear DTCs and repeat QUICK TEST. See RETRIEVING DIAGNOSTIC TROUBLE CODES (QUICK TEST) under SELF-DIAGNOSTIC SYSTEM. Ensure all EEC-IV systems are working properly and DTCs are no longer present.
Perform this test when instructed during QUICK TEST or if directed here by other test procedures. This test is used to diagnose the following: Electronic shift control module wiring harness circuits and faulty PCM. See Fig 1 and Fig 2 .
NOTE:
Electronic shift control module is also referred to as Generic Electronic Module (GEM).
- DTC P1729 indicates open or short in 4WD switch circuit. DTC P1781 indicates 4WD LOW switch position closed during QUICK TEST. If switch position was not 2WD or 4WD HIGH during KOEO SELF-TEST, select 2WD or 4WD HIGH. Repeat RETRIEVING DIAGNOSTIC TROUBLE CODES (QUICK TEST) under SELF-DIAGNOSTIC SYSTEM. If switch position was as specified, go to next step.
- Using NGS tester, select 4WD LOW PID. Turn ignition switch to ON position. Cycle 4WD LOW switch to 2WD. Check for indication of fault while performing the following: Wiggle and bend small sections of wiring harness starting at transfer case working toward PCM. Lightly tap on transfer case wiring harness connector. Wiggle and bend small sections of wiring harness starting at instrument cluster working toward PCM. Fault will be indicated by PID value changing (ON/OFF). If any faults are found, isolate fault. Repair as necessary. If no faults are found, go to next step.
- Turn ignition switch to OFF position. Disconnect PCM 104-pin harness connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition switch to ON position. While cycling 4WD LOW switch, measure voltage between PCM harness connector terminal No. 14 and negative battery terminal. See Figure. If voltage cycles, replace PCM. If voltage does not cycle, go to next step.
- Turn ignition switch to OFF position. Disconnect electronic shift control module harness connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between PCM harness connector terminal No. 14 and 4WD LOW terminal at electronic shift control module harness connector. See Fig 1. If resistance is 5 ohms or less, go to next step. If resistance is more than 5 ohms, repair open in 4WD LOW circuit.
- Reconnect electronic shift control module harness connector. Measure resistance between PCM harness connector terminal No. 14 and negative battery terminal. Measure resistance between PCM harness connector terminals No. 14 and 71. See Figure. If both resistance readings are more than 10 k/ohms, 4WD LOW circuit is okay. Check transfer case for mechanical fault. If any resistance reading is 10 k/ohms or less, repair short in 4WD LOW circuit.