Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 26 other vehicles, including the 1999 Mercury Tracer, 1999 Mercury Sable, 1999 Mercury Mystique, 1999 Mercury Mountaineer, and 1999 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the following:

Electronic shift control module wiring harness circuits. See Fig 1 and Fig 2 .
Powertrain Control Module (PCM).

NOTE: Electronic shift control module is also referred to as Generic Electronic Module (GEM).

Fig 1: Identifying Electronic Shift Control Module Circuit (Electronic Shift)

Courtesy of FORD MOTOR CO.

Fig 2: Identifying 4x4 Low Switch Circuit & Connector Terminals (Mechanical Shift)

Courtesy of FORD MOTOR CO.

1) DTC P1729 & P1781

DTC P1729 indicates open or short in 4x4 switch circuit. DTC P1781 indicates 4x4L switch position closed during QUICK TEST. If switch position was not 4x2 or 4x4H during KOEO SELF-TEST, select 4x2 or 4x4H and repeat QUICK TEST . If switch position was as specified, go to next step.

2) Check Intermittent Circuit Failure

Using scan tool, select 4x4L PID. Turn ignition on. Cycle 4x4L switch to 4x2. 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 and repair as necessary. If no faults are found, go to next step.

3) Check Signal From PCM

Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition on. While cycling 4x4L switch, measure voltage between PCM connector pin No. 14 and negative battery terminal. If voltage cycles, replace PCM. If voltage does not cycle, go to next step.

4) Check 4x4L Circuit Continuity

Turn ignition off. Disconnect electronic shift control module. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between PCM connector pin No. 14 and 4X4L terminal at electronic shift control module wiring 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 4x4L circuit.

5) Check For Short To Power Or Ground

Reconnect electronic shift control module. Measure resistance between PCM connector pin No. 14 and negative battery terminal. Also measure resistance between PCM connector pins No. 14 and 71 (VPWR). If both resistance readings are more than 10,000 ohms, 4x4L circuit is okay. Check transfer case for mechanical fault. If any resistance reading is 10,000 ohms or less, repair short in 4x4L circuit.