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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM & COMPONENT TESTSEMISSION SYSTEMS & SUB-SYSTEMS (GASOLINE)AIR INJECTIONSECONDARY AIR INJECTION SYSTEM DIAGNOSIS (5.0L & 5.7L "C" & "K" SERIES)
1999 GMC Forward Control 5.7 R, Automatic

Secondary Air Injection System Diagnosis (5.0L & 5.7L "C" & "K" Series)

1999 GMC Forward Control 5.7 R, AutomaticSECTION Secondary Air Injection System Diagnosis (5.0L & 5.7L "C" & "K" Series)
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. Turn ignition on with engine off. Using scan tool, command air pump on. If air pump runs, go to next step. If air pump does not run, go to step  9.
  5. Using scan tool, command air pump off. If air pump continues to run, go to next step. If air pump turns off, go to step  20.
  6. Turn ignition off. Remove air pump relay. Turn ignition on with engine off. If air pump continues to run, go to step  35. If air pump turns off, go to next step.
  7. 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  43.
  8. Turn ignition off. Disconnect VCM harness connectors. Turn ignition on with engine off. 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  41. If test light does not illuminate, go to step  47.
  9. Turn ignition off. Disconnect air pump connector. Check for poor connection at air pump. If problem exists, go to step  33. If problem does not exist, go to next step.
    10. NOTE: Two Red wires exist at air pump relay connector. One is a battery feed circuit and the other is the air pump feed circuit.
  10. Turn ignition on with engine off. Using a test light connected to ground, probe air pump feed circuit (Red wire) at air pump connector (engine side). 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 ground circuit (Black wire) at air pump connector (engine side). If test light illuminates, go to step  46. If test light does not illuminate, go to step  34.
  12. Turn ignition off. Disconnect air pump relay connector. Check for poor connection at air pump relay. If problem exists, go to step  33. If problem does not exist, go to next step.
  13. Check for open in air pump feed circuit (Red wire) between air pump relay and air pump. If problem does not exist, go to next step. If problem exist, go to step  33.
  14. Using a test light connected to ground, probe battery feed circuit (Red wire) at air pump relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step  36.
  15. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit (Pink wire) at air pump relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step  37.
  16. 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  43. If test light does not illuminate, go to next step.
  17. Turn ignition off. Disconnect VCM harness connectors. Check for poor connections at VCM. If problem does not exist, go to next step. If problem exist, go to step  33.
  18. Check for open in air pump relay control circuit (Brown wire) between air pump relay and VCM. If problem does not exist, go to next step. If problem exist, go to step  33.
  19. Turn ignition on. Using a test light connected to ground, probe air pump relay control circuit (Brown wire) at air pump relay connector. If test light illuminates, go to step  38. If test light does not illuminate, go to step  47.
  20. Disconnect air pump output hose at air shutoff valve. Start engine and let idle. Using scan tool, command air pump on. If air flows from air shutoff valve, go to next step. If air does not flow from air shutoff valve, go to step  23.
  21. Disconnect vacuum hose from air shutoff valve. Install a vacuum gauge on air shutoff valve vacuum hose. Using scan tool, command air pump off. If vacuum is present at vacuum hose, go to step  45. If vacuum is not present at vacuum hose, go to next step.
  22. Turn ignition off. Turn ignition on with engine off. Using scan tool, command air pump on. If air flows from air shutoff valve, go to step  44. If air does not flow from air shutoff valve, go to step  30.
  23. Turn ignition off. Disconnect air pump output hose from air shutoff valve. Turn ignition on with engine off. 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  31.
  24. Disconnect vacuum hose from air shutoff valve. Install a vacuum gauge on air shutoff valve vacuum hose. Start engine and let idle. Using scan tool, command air pump on. If vacuum is greater than 10 in. Hg while air pump is running, go to step  44. If vacuum is less than 10 in. Hg while air pump is running, go to next step.
  25. Check for leak or restriction in vacuum hose between air solenoid and air shutoff valve. If problem exists, go to step  42. If problem does not exist, go to next step.
  26. Remove vacuum connector from air solenoid. Install a vacuum gauge on source hose coming from engine. Measure vacuum with engine running. If vacuum is greater than 10 in. Hg, go to next step. If vacuum is less than 10 in. Hg, go to step  32.
  27. Turn ignition off. Disconnect air solenoid connector. Check for poor connection at air solenoid. If problem exists, go to step  33. If problem does not exist, go to next step.
  28. Turn ignition on with engine off. Using a test light connected to ground, probe air solenoid feed circuit (Red wire) at air solenoid 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  40.
  29. Turn ignition off. Using a test light connected to battery voltage, probe air solenoid ground circuit (Black wire) at air solenoid connector. If test light illuminates, go to step  45. If test light does not illuminate, go to step  39.
  30. 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  42. 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.
  31. Check for restriction or obstruction in air pump inlet hose. If problem exists, go to step  42. If problem does not exist, go to step  46.
  32. Repair leak or restriction in air solenoid vacuum supply hose. After repairs, go to step  48.
  33. Repair circuit as necessary. After repairs, go to step  48.
  34. Repair open in air pump ground circuit. After repairs, go to step  48.
  35. Repair short to voltage in air pump feed circuit. After repairs, go to step  48.
  36. Repair open or short to ground in air pump relay battery feed circuit. After repairs, go to step  48.
  37. Repair open or short to ground in air pump relay ignition feed circuit. After repairs, go to step  48.
  38. Repair short to voltage in air pump relay control circuit. After repairs, go to step  48.
  39. Repair open in air solenoid ground circuit. After repairs, go to step  48.
  40. Repair open in air solenoid feed circuit. After repairs, go to step  48.
  41. Repair short to ground in air pump relay control circuit. After repairs, go to step  48.
  42. Repair as necessary. After repairs, go to step  48.
  43. Replace air pump relay. After repairs, go to step  48.
  44. Replace air shutoff valve. After repairs, go to step  48.
  45. Replace air solenoid. After repairs, go to step  48.
  46. Replace air pump. After repairs, go to step  48.
  47. 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.
  48. 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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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
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