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TEST FH: 4x4 LOW (EXCURSION & PICKUP): Testing

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    NOTE: For additional testing information, see DIAGNOSTIC AIDS .

  1. 1) DTC P1729 Or P1781: Perform Switch Functional Check
    DTC P1729 indicates that PCM detected a 4x4 low switch error. DTC P1781 indicates PCM detected a 4x4L circuit out of self-test range. Possible cause are:
    • 4x4L Circuit Open Or Shorted To Ground
    • Faulty 4x4 Low Switch Or 4x4 Module
    • Faulty Instrument Cluster
    • Faulty PCM

    Turn ignition on. Observe 4x4L indicator while shifting 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. 2) Check 4x4L Parameter Identification (PID)

    Ensure scan tool is connected to Data Link Connector (DLC). Using scan tool, access 4x4L PID from PID/DATA MONITOR & RECORD menu. Observe 4x4L PID while switching to and from 4x4L. If 4x4L PID agrees with lever position, go to next step. If 4x4L PID does not agree with lever position, diagnose 4x4L circuits and instrument cluster. Go to appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT and repair as necessary. If instrument cluster and related circuits are okay, replace PCM. Clear DTCs and retest.

  3. 3) Check For Intermittent

    While observing 4x4L PID, wiggle and bend all wiring harness circuits for 4x4L. If 4x4L PID switched between ON or OFF states at any time, isolate fault and repair as necessary. Clear DTCs and retest. If 4x4L PID does not switch between ON or OFF states, no concern is indicated at this time. Clear DTCs and retest.

  4. 4) Check Voltage At Switch Or Module

    On models with Manual Shift On The Fly (MSOF), disconnect 4x4 low range switch 2-pin connector. Switch is located on front of transfer case. On models equipped with Electronic Shift On The Fly (ESOF), disconnect 4x4 module 22-pin harness connector C281b. Module is located behind glove box on right side of dash. Using DVOM, measure voltage between chassis ground and Brown/Yellow wire at 4x4 low range switch harness connector (MSOF), or terminal No. 8 at 4x4 module harness connector (ESOF). See Figure. If voltage is more than 10.5 volts, replace 4x4 low range switch (MSOF), or diagnose 4x4L indicator fault (ESOF). See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. If voltage is 10.5 volts or less, go to next step.

  5. 5) Check 4x4L Circuit For Short To Ground

    Ensure 4x4 low range switch (MSOF) or 4x4 module (ESOF) are disconnected. Turn ignition on. Observe 4x4L indicator. If 4x4L indicator remains illuminated with connector disconnected, repair short to ground in Brown/Yellow wire between instrument panel and 4x4 low range switch (MSOF), or 4x4 module (ESOF). If 4x4L indicator does not remain illuminated when connector is disconnected, check low voltage from instrument cluster concern. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. If no problem is found with instrument cluster, replace PCM. Clear DTCs and retest.
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