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Home >> Buick >> 1996 >> LeSabre Custom >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control Systems Tests W/Codes >> Diagnostic Trouble Codes >> DTC P1257 - Supercharger System OVERBOOST >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If any other DTCs set, diagnose affected DTCs before proceeding. If no other DTCs set, go to next step.
  3. Disconnect BC solenoid harness connector. Turn ignition on. Connect a test light across BC solenoid harness connector terminals. If test light illuminates, go to step 9). If test light does not illuminate, go to next step.
  4. Disconnect inlet vacuum signal hose from bypass valve actuator. Connect a vacuum gauge to bypass valve actuator. Start engine and allow it to idle in Park. If vacuum is greater than 12 in. Hg, go to next step. If vacuum is 12 in. Hg or less, go to step 12).
  5. Reconnect BC solenoid harness connector and inlet vacuum signal hose. Disconnect boost signal hose between BC solenoid and by-pass valve actuator. Connect vacuum gauge to bypass valve actuator. Using scan tool, turn BC solenoid off. If vacuum is greater than 12 in. Hg, go to next step. If vacuum is 12 in. Hg or less, go to step 12).
  6. Check for restriction in boost signal hose between BC solenoid and bypass valve actuator. If restriction is found, repair as necessary and go to step 15). If no restriction is found, go to next step.
  7. Check for binding bypass valve, sticking or misadjusted by-pass valve actuator linkage. If problem is found, repair as necessary and go to step 15). If no problem is found, go to next step.
  8. Replace bypass valve actuator and go to step 15).
  9. Turn ignition off. Disconnect PCM. Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step 13).
  10. Locate and repair short to ground in BC solenoid driver circuit and go to step 15).
  11. Repair restriction in inlet vacuum signal hose, or blocked inlet vacuum source and go to step 15).
  12. Check for restriction in boost source hose to BC solenoid. If restriction is found, repair as necessary and go to step 15). If no restriction is found, go to step 12).
  13. Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to step 15).
  14. Replace BC solenoid and go to next step.
  15. Read and record FAIL RECORDS data for DTC P1257. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1257 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1257 FAILED THIS IGN, repair is complete.
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