Diagnostic Aids

Perform this test when directed by QUICK TEST. This test is intended to diagnose:

Fig 1: Identifying 4x4 Low Switch Circuit & Connector Terminals

Courtesy of FORD MOTOR CO.

1) DTC P1729 Or P1781: Perform Switch Functional Check

Turn ignition on. Observe 4x4L indicator and switch to and from 4x4L. If indicator light agrees with lever position, go to next step. If indicator light does not agree with lever position, go to step 4).

2) Check 4x4L Parameter Identification (PID)

Ensure scan tool is connected to Data Link Connector (DLC). Using scan tool, select 4x4L PID from PID/DATA monitor menu. Observe 4x4L PID reading and switch to and from 4x4L. If 4x4L PID reading agrees with lever position, go to next step. If 4x4L PID reading does not agree with lever position, go to step 11).

3) Check For Intermittent

While observing 4x4L PID, wiggle and bend all wiring harness circuits for 4x4L. If 4x4L PID switched states (ON/OFF) at any time, isolate fault and repair as necessary. If 4x4L PID did not switch states, no problem is indicated at this time.

4) Check Voltage At Switch

Disconnect 4x4L switch 2-pin connector. Switch is located on front of transfer case. Measure voltage between ground and Light Blue/Black wire at 4x4L switch wiring harness connector. See Fig 1. If voltage is more than 10.5 volts, replace 4x4L switch. If voltage is 10.5 volts or less, go to next step.

5) Check Indicator Light

Observe 4x4L indicator light and shift to and from 4x4L. If indicator light always stays on, locate and repair short to ground between indicator light and switch connector. If indicator light does not always stay on, go to next step.

6) Check Voltage At Fuse

Measure voltage between ground and both sides of fuse No. 19 at instrument panel fuse block. If battery voltage is present at both readings, go to step 9). If battery voltage is not present at both readings, go to next step.

7) Check Power Feed To Fuse

Measure voltage between ground and power side of No. 19 fuse holder (Red/Light Green wire). If battery voltage is present, go to next step. If battery voltage is not present, repair open circuit in Red/Light Green wire.

8) Check For Short To Ground

Ensure 4x4 lever is not in LOW position. Turn ignition off. Measure resistance between ground and non-powered side of No. 19 fuse holder (Red/Yellow wire). If resistance is more than 10,000 ohms, replace fuse. Clear DTCs and repeat QUICK TEST . If resistance is 10,000 ohms or less, locate and repair short to ground in Red/Yellow wire.

9) Check 4x4L Bulb

Turn ignition off. Remove and inspect 4x4L indicator bulb. Replace bulb as necessary. Clear DTCs and repeat QUICK TEST . If bulb is okay, go to next step.

10) Check Voltage At Indicator Bulb

Turn ignition on. Shift out of 4x4 Low. Measure voltage between ground and Red/Yellow wire at indicator bulb socket. If battery voltage is present, locate and repair open circuit in Light Blue/Black wire between indicator bulb and 4x4L switch. If battery voltage is not present, locate and repair open circuit in Red/Yellow wire between fuse and indicator bulb.

11) Check Circuit No. 784

Turn ignition off. Disconnect PCM 104-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Disconnect 4x4L switch connector. Measure resistance between Light Blue/Black wire at 4x4L switch wiring harness connector and test pin No. 14 at breakout box. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, locate and repair open circuit in Light Blue/Black wire.

12) Check For Short To Ground

Measure resistance between ground and Light Blue/Black wire at 4x4L switch wiring harness connector. If resistance is less than 10,000 ohms, locate and repair short to ground in Light Blue/Black wire. If resistance is 10,000 ohms or more, replace PCM. Clear DTCs and repeat QUICK TEST.