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TEST TG: 4x4 LOW RANGE: Testing

    NOTE: For additional testing information, see DIAGNOSTIC AIDS .
    NOTE: Transmission Range (TR) sensor must indicate Neutral before shifting into 4WD LOW.

  1. 1) For KOEO Only DTC P1781: Verify 4x4L Switch Position
    DTC P1729 is set when PCM receives too high of a voltage on 4WD LOW circuit when 4x4L switch is ON (indicating open or short in 4WD switch circuit). DTC P1781 indicates 4x4L switch position closed during QUICK TEST. Possible causes are:
    • 4WD LOW Circuit Open Or Shorted
    • Faulty Electronic Shift Control Module
    • Faulty Powertrain Control Module (PCM)

    Ensure vehicle is equipped with 4WD. If switch was not in 2WD or 4WD HIGH position during KOEO self-test, select 2WD or 4WD HIGH and repeat QUICK TEST . If switch position was as specified, go to next step.

  2. 2) Check 4WD LOW Circuit For Intermittent Fault

    Connect scan tool to Data Link Connector (DLC). Turn ignition switch to ON position. Using scan tool, access 4x4L PID from PID/DATA MONITOR & RECORD menu. Cycle 4x4L switch to 2WD. Check for indication of fault while performing the following:
    • Shake, wiggle and bend small sections of wiring harness starting at transfer case working toward PCM.
    • Lightly tap on transfer case harness connector.
    • Shake, wiggle and bend small sections of wiring harness starting at instrument cluster working toward PCM.

    A fault will be indicated by 4x4L PID value changing from OFF to ON. If any faults are found, isolate fault and repair as necessary. If no faults are found, go to next step.

  3. 3) Check 4WD LOW Signal Voltage To PCM

    Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector(s) for loose, damaged or corroded terminals. Repair as necessary. Turn ignition switch to ON position. While cycling 4x4L switch, measure voltage between negative battery terminal and 4WD LOW circuit at PCM harness connector. See WIRING DIAGRAMS . If voltage cycles with 4x4L switch position, replace PCM. If voltage does not cycle with 4x4L switch position, go to next step.

  4. 4) Check 4WD LOW Circuit For Open In Harness

    Turn ignition switch to OFF position. Disconnect electronic shift control module. See 4-WHEEL DRIVE SHIFT CONTROL MODULE  table. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. On electronic shift models, measure resistance of 4WD LOW circuit between PCM harness connector and electronic shift control module harness connector. See WIRING DIAGRAMS . On mechanical shift models, measure resistance of 4WD LOW circuit between PCM harness connector, instrument cluster and 4x4L switch. See WIRING DIAGRAMS . If all resistances are 5 ohms or less, go to next step. If any resistance is more than 5 ohms, repair open in 4WD LOW circuit.

  5. 5) Check 4WD LOW Circuit For Short To PWR Or GND In Harness

    Reconnect electronic shift control module. Using a DVOM, measure resistance between 4WD LOW circuit, and VPWR circuit at PCM harness connector and negative battery terminal. If both resistance measurements are more than 10 k/ohms, 4WD LOW circuit is okay. Check transfer case for mechanical fault. See appropriate DIAGNOSIS or OVERHAUL article in TRANSFER CASES for further diagnosis. If either resistance measurement is 10 k/ohms or less, repair short in 4WD LOW circuit.
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