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Home >> Buick >> 1996 >> Century Custom >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests - 3.1L >> C-10 & C-12 Diagnostic Tests >> C-12, Cooling Fan Circuit Diagnosis >> Cooling Fan Circuit Diagnosis

Cooling Fan Circuit Diagnosis

  1. Perform On-Board Diagnostics (OBD) System check. See BASIC TESTING article. After performing OBD system check, go to next step.
  2. Check for PCM Diagnostic Trouble Codes (DTCs). If any codes are present, perform testing for applicable code. Repair all DTCs that are present before proceeding with testing. See TESTS W/CODES article. If no codes are present, go to next step.
  3. Ensure engine coolant temperature is less than 212°F (100°C). Turn A/C off. Turn ignition on. If cooling fans go off, go to next step. If cooling fans do not go off, go to step 43).
  4. Select scan tool MISC. TESTS, RELAY CONTROL function, and command fan No. 1 on. If fan comes on, go to next step. If fan does not come on, go to step 6).
  5. Select scan tool MISC. TESTS, RELAY CONTROL function and command fan No. 2 on. If fan No. 2 does not come on, go to step 19). If fan No. 2 does come on, system is operating normally.
  6. Remove fan No. 1 relay from right underhood electrical center. Turn ignition on, engine off. Connect test light between fan relay connector terminals No. 85 (Pink wire) and No. 86 (Dark Green wire). Select scan tool MISC. TESTS, RELAY CONTROL function and command fan No. 1 on. If test light illuminates, go to next step. If test light does not illuminate, go to step 15).
    NOTE: Ambient temperature must be greater than 48°F (9°C) before PCM will enable cooling fans due to A/C request. PCM will enable cooling fans if A/C refrigerant pressure increases regardless of ambient temperature.
  7. Check for blown Blue maxi-fuse No. 3 (60-amp). If fuse is blown, go to step 19). If fuse is not blown, go to next step.
  8. Connect test light between ground and fan No. 1 relay connector terminal No. 30 (Red wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
  9. Locate and repair open battery feed circuit to terminal No. 30 (Red wire) in fan No. 1 relay connector. Go to step 56).
  10. Turn ignition off. Connect a 20-amp fused jumper wire between terminals No. 30 (Red wire) and No. 87 (Light Blue wire) in fan No. 1 relay connector. If fan No. 1 is running, go to next step. If fan No. 1 is not running, go to step 53).
  11. Disconnect fan No. 1 electrical connector. Install 20-amp fused jumper wire between fan No. 1 relay connector terminals No. 30 (Red wire) and No. 87 (Light Blue wire). Connect test light between fan No. 1 harness connector terminals. If test light illuminates, go to step 52). If test light does not illuminate, go to next step.
  12. Connect test light between battery voltage and cooling fan motor No. 1 ground circuit at fan No. 1 connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 14).
  13. Locate and repair open circuit in engine cooling fan motor No. 1 voltage circuit. Go to step 56).
  14. Locate and repair open circuit in engine cooling fan motor No. 1 ground circuit. Go to step 56).
  15. Connect test light between ground and fan No. 1 relay connector terminal No. 85 (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 17).
  16. Turn ignition off. Disconnect PCM connector. Connect test light between terminals No. 85 (Pink wire) and No. 86 (Dark Green wire) at fan No. 1 relay connector. Connect jumper wire between fan No. 1 relay driver circuit and ground at PCM connector. If test light illuminates, go to step 51). If test light does not illuminate, go to step 18).
  17. Locate and repair open circuit in battery feed circuit to terminal No. 85 (Pink wire) in fan No. 1 relay connector. Go to step 56).
  18. Locate and repair open circuit in fan No. 1 relay driver circuit. Go to step 56).
  19. Remove Blue maxi-fuse fuse No. 3 (60-amp). Connect a test light between voltage and fan No. 1 relay connector terminal No. 30 (Red wire) at fan No. 1 relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 21).
  20. Locate and repair short to ground in battery feed circuit to terminal No. 30 (Red wire) in fan No. 1 relay connector. Go to step 56).
  21. Disconnect engine cooling fan motor No. 1 connector. Connect test light between battery voltage and terminal No. 87 (Light Blue wire) at fan No. 1 relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 52).
  22. Locate and repair short to ground in engine cooling fan motor No. 1 feed circuit. Go to step 56).
  23. Remove fan No. 2 relay from right underhood electrical connector. Turn ignition on, engine off. Connect test light between terminals No. 85 and No. 86 in relay connector. Select scan tool MISC. TEST, RELAY CONTROL function and command fan No. 2 on. If test light illuminates, go to next step. If test light does not illuminate, go to step 32).
  24. Check for a blown Blue maxi-fuse No. 3 (60-amp) that feeds fan No. 2 relay terminal No. 30. If fuse is blown, go to step 39). If fuse is not blown, go to next step.
  25. Connect a test light to ground. Probe terminal No. 30 in fan No. 2 relay connector. If test light illuminates, go to step 27). If test light does not illuminate, go next step.
  26. Locate and repair open in feed circuit to fan No. 2 relay, terminal No. 30. Go to step 56).
  27. Turn ignition off. Connect a 20-amp fused jumper between terminals No. 30 and No. 87 at fan No. 2 relay connector. Turn ignition on. If fan No. 2 is on, go to step 54). If fan No. 2 is not on, go to next step.
  28. Disconnect the engine cooling fan motor No. 2 electrical connector. Connect a 20-amp fused jumper wire between terminals No. 30 and 87 at fan No. 2 relay connector. Connect a test light between the engine cooling fan motor No. 2 connector terminals. If test light illuminates, go to step 54). If test light does not illuminate, go to next step.
  29. Connect a test light to battery voltage. Probe ground circuit terminal at engine cooling fan motor No. 2 connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 31).
  30. Locate and repair open in engine cooling fan motor No. 2 feed circuit. Go to step 56).
  31. Locate and repair open in engine cooling fan motor No. 2 ground circuit. Go to step 56).
  32. Check fuse that feeds fan No. 2 relay terminal No. 85. If fuse is blown, go to next step. If fuse is not blown, go to step No. 35).
  33. Remove in-line fuse (10-amp) that feeds fan No. 2 relay terminal No. 85. Probe terminal No. 85 at fan No. 2 relay connector with a test light to voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 55).
  34. Locate and repair short to ground in feed circuit to fan No. 2 relay terminal No. 85. Go to step 56).
  35. Probe terminal No. 85 in fan No. 2 relay connector with a test light to ground. If test light illuminates, go next step. If test light does not illuminate, go to step 37).
  36. Turn ignition off. Disconnect PCM connector. Connect a test light between terminal No. 85 and No. 86. at fan No. 2 relay connector. Jumper fan No. 2 relay driver circuit to ground at PCM connector. If test light illuminates, go to step 51). If test light does not illuminate, go to step 38).
  37. Locate and repair open circuit in feed circuit to fan No. 2 relay connector terminal No. 85. Go to step 56).
  38. Locate and repair open circuit in fan No. 2 driver circuit. Go to step 56).
  39. Remove Blue maxi-fuse No. 1 (60-amp). Connect a test light to battery voltage. Probe terminal No. 30 at fan No. 2 relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 41).
  40. Locate and repair short to ground in feed circuit to fan No. 2 relay connector terminal No. 30. Go to step 56).
  41. Disconnect engine cooling fan motor No. 2 connector. Probe terminal No. 87 in fan No. 2 relay connector with a test light to voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 54).
  42. Locate and repair short to ground in engine cooling fan motor No. 2 feed circuit. Go to step 56).
  43. If both cooling fans are on, go to next step. If both fans are not on, go to step 45).
  44. Turn ignition off. Disconnect A/C pressure sensor. Turn ignition on. Using scan tool, monitor A/C pressure. If scan tool shows zero psi (0 kg/cm2 ), go to step 49). If scan tool does not show zero psi (0 kg/cm2 ), go to step 51).
  45. If fan No. 1 is on, go to next step. If fan No. 1 is not on, go to step 50).
  46. Use scan tool and monitor A/C pressure. If scan tool shows pressure greater than 190 psi (13.4 kg/cm2 ), go to step 47). If scan tool does not show pressure greater than 190 psi (13.4 kg/cm2 ), go to step 48).
  47. Disconnect A/C pressure sensor. Using scan tool, monitor A/C pressure. If scan tool shows zero psi, go to step 49). If scan tool does not show zero psi, go to step 51).
  48. Locate and repair short to voltage in engine cooling fan motor No. 1 feed circuit. Go to step 56).
  49. Replace A/C pressure sensor. Go to step 56).
  50. Locate and repair short to voltage in engine cooling fan motor No. 2 feed circuit. Go to step 56).
  51. Replace PCM. Go to step 56).
  52. Replace engine cooling fan motor No. 1. Go to step 56).
  53. Replace fan No. 1 relay. Go to step 56).
  54. Replace engine cooling fan motor No. 2. Go to step 56).
  55. Replace fan No. 2 relay. Go to step 56).
  56. Ensure engine coolant is less than 212°F (100°C). Turn A/C switch off. Turn ignition on. If fans are off, go to next step. If fans are not off, go to step 3).
  57. Select scan tool MISC. TESTS, RELAY CONTROL function and command fan No. 1 on. If fan comes on, go to next step. If fan does not come on, go to step 6).
  58. Select scan tool MISC. TESTS, RELAY CONTROL function and command fan No. 2 on. If fan comes on, system is operating normally at this time. If fan does not come on, go to step 19).
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