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Home >> Buick >> 1996 >> Roadmaster Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control Systems - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P1509 - IAC System High Rpm >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
  2. Start engine. Using scan tool, command RPM from 500 to 1500 RPM. Repeat 2 times and the exit from test. If RPM change responded to within 50 RPM with each command, see DIAGNOSTIC AIDS. If RPM does not respond as commanded, go to next step.
  3. Turn ignition off. Disconnect IAC harness connector and install IAC Noid Light (J 37027-A). Start engine. Using scan tool, command RPM up to 1500 down to 500 and up to 1500 RPM, while observing noid light. If noid lights cycle Red and Green, but never off, go to next step. If noid light LEDs do not cycle, go to step 5).
  4. Turn ignition off. Remove IAC valve from throttle body. Connect IAC valve to IAC Driver Tool (J 37027-A). Hold finger over IAC pintle to avoid over extension. Using driver, retract and extend pintle. If IAC pintle moves steadily, go to step 6). If pintle does not move or movement is erratic, go to step 7).
  5. Check for faulty connection, open circuit or circuit shorted to ground or battery voltage. Repair as necessary. After repairs, go to step 8).
  6. Check IAC passage in throttle body. Clean as necessary. After repairs, go to step 8).
  7. Replace IAC valve. After replacing IAC valve, go to next step.
  8. Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1509. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool did not indicate that this test ran and passed, repeat step 2).
  9. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
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