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Home >> GMC >> 2000 >> Envoy >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 4.3L >> Diagnostic Tests >> DTC P1621: Control Module Long Term Memory Performance >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC SYSTEM CHECK . After performing OBD system check, go to next step.
  2. Replace VCM. Program replacement VCM using required equipment and perform Crankshaft Variation Learn Procedure. After replacing VCM, go to next step.
  3. Using scan tool, select DTC and CLEAR DTC INFO function. Warm engine to normal operating temperature. Operate engine at idle. Using scan tool, select DTC and SPECIFIC DTC function, then enter this DTC. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step  2.
  4. Check if any additional DTC(s) are present. If additional DTCs are present, diagnose affected DTC(s) first. If no other DTCs are present, system is okay.