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Diagnostic Procedures

WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 1998 GMC Savana Special, 1998 GMC Savana Camper Special, 1998 GMC Savana, 1998 Chevrolet RV Cutaway, and 1998 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
  1. Connect scan tool to DLC. Turn ignition switch to ON position. DO NOT start engine. Using scan tool, record freeze frame and failure records for reference. Data will be lost when DTCs are cleared later in this test.
  2. Set parking brake and block drive wheels. Shift transmission into Neutral. While observing scan tool 4WD low display, select 4HI on transfer case selector switch, then select 4LO. If scan tool 4WD low does not display NO when 4HI is selected and YES when 4LO is selected, go to next step. If scan tool 4WD low displays NO when 4HI is selected and YES when 4LO is selected, see DIAGNOSTIC AIDS.
  3. Turn ignition off. Disconnect transfer case switch connector. Turn ignition switch to ON position. If scan tool 4WD low does not indicate YES, go to next step. If scan tool 4WD low indicates YES, check for short to ground in 4WD low signal circuit. See procedures in WIRING DIAGRAMS . Repair as necessary, then go to step 6). If circuit is okay, check VCM connector for bent, backed out, deformed or damaged terminals. Repair as necessary, then go to step 6). If terminals and connections are okay, replace VCM, then go to step 6).
  4. Connect terminal "B" (Gray/Black wire) of transfer case selector switch connector to good known ground. Observe scan tool 4WD low. If scan tool 4WD low indicates YES when circuit is grounded, replace transfer case selector switch, then go to step 6).
  5. If scan tool 4WD low does not indicate YES when circuit is grounded, check for open in 4WD low signal circuit. Repair as necessary, then go to next step. If circuit is okay, check VCM connector for bent, backed out, deformed or damaged terminals. Repair as necessary, then go to next step. If terminals and connections are okay, replace VCM, then go to next step.
  6. After repair is complete, select DTC on scan tool. Select "Clear Info" function. Operate vehicle under following conditions. Select 4LO on selector switch. Drive vehicle. Gear ratio must be 2.65-2.75 for one second in 4th gear with TCC locked. Select 4HI on selector switch. Drive vehicle. Gear ratio must be 0.95-1.05 for one second in any gear. Select "Specific DTC" and enter DTC "P1875". If DTC P1875 is not present, repair is complete. If DTC P1875 is still present, repeat test.
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