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Secondary Air Injection System Diagnosis (7.4L)

NOTE: For circuit and connector terminal identification, see appropriate wiring diagram in WIRING DIAGRAMS article.
  1. If On-Board Diagnostic (OBD) system check has been performed, go to next step. If On-Board Diagnostic (OBD) system check has not been performed, perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.
  2. Install scan tool. Start engine and let idle until normal operating temperature is obtained. Using scan tool, verify engine is at normal operating temperature and operating in closed loop. Using scan tool, command air pump on. If short term fuel trim indicates 16 percent within 30 seconds, go to next step. If short term fuel trim does not indicate 16 percent within 30 seconds, go to step  4.
  3. If any DTCs exist, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article. If no DTCs exist, check the following and repair as necessary.
    • Loose air pump belt.
    • Poor connection at PCM or any secondary air injection system component.
    • Damaged wiring harness.
    • Pinched, kinked or restricted air pipes, line or fittings.
  4. Ensure engine is still running. Using scan tool, command air pump on. If air pump clutch is engaged, go to next step. If air pump clutch is not engaged, go to step  9.
  5. Ensure engine is still running. Using scan tool, command air pump off. If air pump clutch is engaged, go to next step. If air pump clutch is not engaged, go to step  19.
  6. Turn ignition off. Remove air pump relay. Turn ignition switch on. Using a test light connected to battery voltage, probe air pump relay control circuit (Brown wire) at air pump relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step  8.
  7. Turn ignition off. Disconnect VCM harness connectors. Using a test light connected to battery voltage, probe air pump relay control circuit (Brown wire) at air pump relay connector. If test light illuminates, go to step  30. If test light does not illuminate, go to step  36.
  8. Turn ignition on. Using a test light connected to ground, probe air pump feed circuit (Red wire) at air pump relay connector. If test light illuminates, go to step  31. If test light does not illuminate, go to step  33.
  9. Turn ignition off. Disconnect air pump clutch connector. Check for poor connection at air pump clutch. If problem exists, go to step  26. If problem does not exist, go to next step.
  10. Turn ignition on with engine off. Using a test light connected to ground, probe air pump clutch feed circuit (Red wire) at air pump clutch connector. Using scan tool, command air pump on. If test light illuminates, go to next step. If test light does not illuminate, go to step  12.
  11. Using a test light connected to ground, probe air pump clutch ground circuit (Black wire) at air pump clutch connector. If test light illuminates, go to step  35. If test light does not illuminate, go to step  27.
  12. Turn ignition off. Disconnect air pump relay connector. Check for poor connection at air pump relay. If problem exists, go to step  26. If problem does not exist, go to next step.
  13. Check for open in air pump clutch feed circuit. If problem exists, go to step  26. If problem does not exist, go to next step.
  14. Turn ignition on. Using a test light connected to ground, probe both ignition feed circuits (Pink wires) at air pump relay socket. If test light illuminates on both terminals, go to next step. If test light does not illuminate on both terminals, go to step  28.
  15. Using a test light connected to battery voltage, probe air pump relay control circuit (Brown wire) at air pump relay connector. Using scan tool, command air pump on. If test light illuminates, go to step  33. If test light does not illuminate, go to next step.
  16. Turn ignition off. Disconnect VCM harness connector. Check for poor connection at VCM. If problem exists, go to step  26. If problem does not exist, go to next step.
  17. Check for open in air pump relay control circuit. If problem exists, go to step  26. If problem does not exist, go to next step.
  18. Turn ignition on. Using a test light connected to ground, probe air pump relay control circuit (Brown wire) at VCM harness connector. If test light illuminates, go to step  29. If test light does not illuminate, go to step  36.
  19. Turn ignition off. Disconnect air output hose at output of air shutoff valve. Start engine and let idle. Using scan tool, command air pump on. If air flows from air shutoff valve, go to step  24. If air does not flow from air shutoff valve, go to next step.
  20. Turn ignition off. Disconnect air output hose at inlet of air shutoff valve. Start engine and let idle. Using scan tool, command air pump on. If air flows from output hose, go to next step. If air does not flow from output hose, go to step  23.
  21. Using scan tool, command air pump on. Accelerate engine to about 1500 RPM. If airflow increases as engine is accelerated, go to next step. If airflow does not increase as engine is accelerated, go to step  25.
  22. Check for leaks or loose connections in hose between air pump and air shutoff valve. If problem exists, go to step  32. If problem does not exist, go to step  34.
  23. Check for leaks or obstructions in hose between air pump and air shutoff valve. If problem exists, go to step  32. If problem does not exist, go to step  25.
  24. Check for leaks or restrictions in air shutoff valve, hoses, check valves, fittings, air pipes, and/or exhaust manifolds. If problem exists, go to step  32. If problem does not exist, check the following and repair as necessary.
    • Loose air pump belt.
    • Poor connection at PCM or any secondary air injection system component.
    • Damaged wiring harness.
    • Pinched, kinked or restricted air pipes, line or fittings.
  25. Check for restriction or obstruction in air pump inlet hose. If problem exists, go to step  32. If problem does not exist, go to step  35.
  26. Repair circuit as necessary. After repairs, go to step  37.
  27. Repair open in air pump clutch ground circuit. After repairs, go to step  37.
  28. Repair open or short to ground in ignition feed circuits. After repairs, go to step  37.
  29. Repair short to voltage in air pump relay control circuit. After repairs, go to step  37.
  30. Repair short to ground in air pump relay control circuit. After repairs, go to step  37.
  31. Repair short to voltage in air pump clutch feed circuit. After repairs, go to step  37.
  32. Repair as necessary. After repairs, go to step  37.
  33. Replace air pump relay. After repairs, go to step  37.
  34. Replace air shutoff valve. After repairs, go to step  37.
  35. Replace air pump. After repairs, go to step  37.
  36. Replace VCM. Program VCM. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step.
  37. Install scan tool. Start engine and let idle until normal operating temperature is obtained. Using scan tool, verify engine is at normal operating temperature and operating in closed loop. Using scan tool, command air pump on. If short term fuel trim indicates 16 percent within 30 seconds, system is okay. If short term fuel trim does not indicate 16 percent within 30 seconds, go to step  4.
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