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Home >> Chevrolet >> 1998 >> Astro Van Cargo, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0101 - MAF Sensor System Performance >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . Retrieve and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. After performing OBD system check, go to next step.
  2. Turn ignition on, with engine off. Using scan tool, monitor MAP sensor display. If MAP sensor value is greater than 100 kPa, go to next step. If MAP sensor value is not greater than 100 kPa, go to step 20).
    NOTE: Always replace MAP sensor seal when sensor is removed.
  3. Remove MAP sensor from intake manifold. Leave sensor connector connected. Connect a hand-held vacuum pump to MAP sensor. Slowly apply vacuum to sensor (up to 20 in. Hg). Observe MAP sensor reading on scan tool. Each inch of vacuum applied to sensor should result in 3-4 kPa drop in MAP sensor value. Value should change smoothly with each vacuum increment. If MAP sensor value changes smoothly, go to next step. If MAP sensor value does not change smoothly or is erratic, go to step 20).
  4. Apply 20 in. Hg to MAP sensor. If scan tool reads 34 kPa or less, go to next step. If scan tool does not read 34 kPa or less, go to step 20).
  5. Disconnect vacuum source from MAP sensor. If MAP sensor reading returns to original value, go to next step. If MAP sensor reading does not return to original reading, go to step 20).
  6. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORD data. Operate vehicle within conditions noted in FAIL RECORD data. Using scan tool, read SPECIFIC DTC. If scan tool displays that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see DIAGNOSTIC AIDS.
  7. Check for throttle body inlet screen blockage. Check for vacuum leaks at intake manifold, throttle body or EGR valve flange and pipes. Check for crankcase valve faulty, missing or incorrectly installed. Repair faulty conditions as necessary. After repairs, go to step 22). If no faulty conditions exist, go to next step.
  8. Turn ignition on, throttle closed. Using scan tool, read TP ANGLE value. If scan tool displays about zero percent, go to next step. If scan tool does not display zero percent, go to DTC P0121 for diagnosis.
  9. Turn ignition off. Disconnect MAF sensor harness connector. Turn ignition on, engine off. Using a DVOM, check voltage between MAF sensor harness connector signal circuit and chassis ground. If voltage is about 5 volts, go next step. If voltage is not as specified, go to step 11).
  10. Connect a test light between MAF sensor harness connector ignition feed and ground circuits. If test light illuminates, go to step 14). If test light does not illuminate, go to step 13).
  11. If voltage is less than 4.5 volts, go to step 15). If voltage is not less than 4.5 volts, go to next step.
  12. Turn ignition off. Disconnect VCM connectors. Turn ignition on, engine off. Check voltage between VCM harness connector MAF signal circuit and chassis ground. If voltage reading is about zero volts, go to step 21). If voltage is not about zero volts, go to step 18),
  13. Connect test light between MAF sensor harness connector ignition feed circuit and chassis ground. If test light illuminates, go to step 16). If test light does not illuminate, go to step 17).
  14. Check for faulty connection at MAF sensor. Repair as necessary. After repairs, go to step 22). If connection is okay, go to step 17).
  15. Check MAF sensor signal circuit between VCM and MAF sensor for open or shorted circuit to ground. Repair as necessary. After repairs, go to step 22). If circuit is okay, go to step 21).
  16. Repair open in the MAF sensor ground circuit. After repairs, go to step 22).
  17. Repair open MAF sensor ignition feed circuit. After repairs, go to step 22).
  18. Repair short to voltage in MAF sensor signal circuit. After repairs, go to step 22).
  19. Replace MAF sensor. After replacing sensor, go to step 22).
  20. Replace MAP sensor. After replacing sensor, go to step 22).
  21. Replace VCM. Program replacement VCM using required equipment. Perform password learn procedures. After replacing VCM, go to next step.
  22. Using scan tool, select DTC, CLEAR INFO function. Start engine and allow it to reach operating temperature. Using scan tool, select DTC, SPECIFIC function and enter this DTC. Operate vehicle within conditions required to set DTC. If scan tool displays RAN AND PASSED, go to next step. If scan tool does not display RAN AND PASSED, return to step 2).
  23. Using scan tool, display CAPTURE INFO and REVIEW CAPTURE INFO function. If any additional DTCs are set, diagnose affected DTCs. If no additional DTCs are set, system is okay.
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