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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 59 (Automatic Transmission Diagnosis - 4L80-E) >> Diagnostic Tests >> DTC P1875: 4WD Low Switch Circuit - Electrical Malfunction >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 Chevrolet Suburban, and 2002 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the diagnostic system check? If so, go to next step. If not, see DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Install a scan tool. Turn ignition on, engine off. Before clearing the DTCs, use the scan tool to record the freeze frame and failure records. Using the CLEAR INFO function erases the freeze frame and failure records from the PCM. Record the freeze frame and failure records. Clear the DTCs. Place the transmission in Neutral. Select 4WD, then 4WD Low on the transfer case selector lever. Does the 4WD LOW on the scan tool display DISABLED when 4WD is selected, then ENABLED when 4WD LOW is selected? If so, see DIAGNOSTIC AIDS . If not, go to next step.
  3. Turn ignition off. Disconnect the active transfer case control module connector (active transfer case vehicles) or the transfer case switch connector (non-active transfer case vehicles). Turn ignition on, engine off. Does the 4WD LOW on the scan tool indicate ENABLED? If so, go to step  6. If not, go to next step.
  4. Ground connector C1 terminal F7 of the active transfer case control module connector (active transfer case vehicles) or terminal "B" of the transfer case switch connector (non-active transfer case vehicles) to ground. Ensure that the scan tool displays 4WD LOW. Does 4WD LOW on the scan tool indicate ENABLED when the signal circuit (1694) is grounded? If so, go to next step. If not, go to step  7.
  5. Replace the active transfer case control module on the active transfer case vehicles or the transfer case switch on the non-active transfer case vehicles. See appropriate DIAGNOSIS article in TRANSFER CASES. Did you complete the replacement? If so, go to step  9.
  6. Test the signal circuit (1694) for a short to ground. Repair the circuit if necessary. Did you find and correct the condition? If so, go to step  9. If not, go to step  8.
  7. Test the signal circuit (1694) for an open. Repair the circuit if necessary. Did you find and correct the condition? If so, go to step  9. If not, go to next step.
  8. Replace the PCM. See POWERTRAIN CONTROL MODULE  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to next step.
  9. Perform the following procedure to verify the repair:
    • Select DTC.
    • Select CLEAR INFO.
    • Select 4WD Low on the 4WD selector and drive the vehicle.
    • The transfer case gear ratio must be 2.68-2.76 for one second in 4th gear with the TCC locked.
    • Select 4WD on the selector and drive the vehicle.
    • The gear ratio must be 0.95-1.05 for 0.5 second in any one gear.
    • Select SPECIFIC DTC.
    • Enter DTC P1875.

    Has the test run and passed? If so, system is okay. If not, go to step  1.

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