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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> Transmission >> Automatic Trans >> Automatic Transmission Diagnosis - 4L60-E >> Diagnostic Tests >> DTC P1875: 4WD Low Switch Circuit - Electrical Malfunction >> Diagnostic Procedure

Diagnostic Procedure

  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. Connect scan tool to DLC. Turn ignition on, engine off. Using scan tool, record freeze frame and failure records for reference, and then clear DTCs. Set parking brake and block drive wheels. Shift transmission into Neutral. While monitoring scan tool 4WD low display, select 4HI, and then 4LO on transfer case selector switch. If scan tool displays DISABLED when 4HI is selected and ENABLED when 4LO is selected, see DIAGNOSTIC AIDS . If scan tool does not display DISABLED when 4HI is selected and ENABLED when 4LO is selected, go to next step.
  3. Turn ignition off. Disconnect transfer case switch harness connector or TCCM harness connector (if equipped). Turn ignition on, engine off. If scan tool indicates ENABLED, go to step  6. If scan tool does not indicate ENABLED, go to next step.
  4. Using fused jumper wire, connect 4WD low signal circuit to ground. See WIRING DIAGRAMS . If scan tool indicates ENABLED, go to next step. If scan tool does not indicate ENABLED, go to step  7.
  5. Replace transfer case switch or TCCM, if equipped. After repairs, go to step  9.
  6. Check 4WD low signal circuit for short to ground. Repair as necessary. After repairs, go to step  9. If circuit is okay, go to step  8.
  7. Check for open in 4WD low signal circuit. Repair as necessary. After repairs, go to step  9. If circuit is okay, go to next step.
  8. Replace PCM. After replacement, program PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article in ENGINE PERFORMANCE. After repairs, go to next step.
  9. Using scan tool, clear DTCs. Operate vehicle under following conditions: Select 4LO on transfer case selector switch. Drive vehicle in "D4" range. Ensure transfer case ratio is 2.5-2.9 for 5 seconds. Select 2HI or 4HI on transfer case selector switch. Drive vehicle in "D4" range with TCC on. Ensure transfer case ratio is .8-1.2 for 5 seconds. Check for DTCs. If DTC P1875 does not return, system is okay. If DTC P1875 returns, repeat step  1.
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