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Home >> Pontiac >> 1995 >> Firebird Formula, 2D Convertible, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests - 3.8L >> 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 if any Diagnostic Trouble Codes (DTCs) are stored. If codes are stored, diagnose DTC(s). See TESTS W/CODES article. If DTC(s) are present, go to next step.
  3. Ensure engine coolant temperature is less than 212°F (100°C). Turn A/C off. Start and idle engine. If fans are off, go to next step. If fans are not off, go to step 24).
  4. Using scan tool OUTPUT TESTS function, activate FAN 1. If both fans run at low speed, go to next step. If both fans do not run at low speed, go to step 8).
  5. Using scan tool OUTPUT TESTS function, activate FAN 2. If both fans run at high speed, go to next step. If both fans do not run at high speed, go to step 34).
  6. Ensure ambient temperature is greater than 60°F (15°C). Exit scan tool OUTPUT TESTS. Start and run engine. Turn A/C on. If fans come on, system is operating correctly. Problem may be intermittent. If fans do not come on, go to next step.
  7. Using scan tool, view A/C REQUEST. If scan tool displays YES, go to step 69). If scan tool does not display YES, perform A/C clutch control circuit diagnosis.
  8. Remove low speed cooling fan relay No. 1 from under electrical center. Using a test light connected to ground, probe terminal D1 (Red wire). If test light illuminates, go to step 10). If test light does not illuminate, go to next step.
  9. Repair open in battery feed circuit to low speed cooling fan relay No. 1, terminal D1 (Red wire). Go to step 73).
  10. Using a test light connected to ground, probe low speed cooling fan relay No. 1 terminal D5 (Orange wire). If test light illuminates, go to step 12). If test light does not illuminate, go to next step.
  11. Locate and repair open in battery feed circuit to low speed cooling fan relay No. 1, terminal D5 (Orange wire). Go to step 73).
  12. Disconnect both cooling fans. Jumper terminals "A" (Black wire) and "B" (Light Blue or Brown wire) together at both cooling fan connectors. Connect a test light between terminals D1 (Red wire) and D4 (Light Blue wire) in underhood electrical center. If test light illuminates, go to next step. If test light does not illuminate, go to step 19).
  13. Connect test light between terminals D2 (Dark Green wire) and D5 (Orange wire) in underhood electrical center. Turn ignition on. Using scan tool OUTPUT TESTS function, activate FAN 1. If test light illuminates, go to next step. If test light does not illuminate, go to step 17).
  14. Turn ignition off. Remove jumpers from cooling fan connectors and reconnect fans. Install fused jumper wire between terminals D1 (Red wire) and D4 (Light Blue wire) in underhood electrical center. Turn ignition on. If fans come on, go to next step. If fans do not come on, go to step 16).
  15. Check for poor connections at low speed cooling fan relay No. 1. If a repair was made, go to step 73). If a repair was not made, go to step 31).
  16. Check for poor connections at fan No. 1 or fan No. 2 fan motors. If a repair was made, go to step 73). If a repair was not made, go to step 19).
  17. Turn ignition off. Disconnect PCM Blue connector. Install a fused jumper wire between terminals D2 (Dark Green wire) and D5 (Orange wire) in underhood electrical center. Probe PCM connector terminal C1-32 (Dark Green wire) with a test light to ground. If test light illuminates, go to step 69). If test light does not illuminate, go to next step.
  18. Repair open in fan No. 1 (low speed) driver circuit between PCM and underhood electrical center. Go to step 73).
  19. Turn ignition off. Remove jumper wires from cooling fan connectors and reconnect fans. Install a fused jumper wire between terminals D1 (Red wire) and D4 (Light Blue wire) in underhood electrical center. Remove series/parallel cooling fan relay No. 3 from underhood electrical center. Connect test light to ground and probe terminal J4 (Black wire) in underhood electrical center. If test light illuminates, go to next step. If test light does not illuminate, go to step 23).
  20. Connect a test light between terminals J3 (Brown wire) and J4 (Black wire) in underhood electrical center. If test light illuminates, go to next step. If test light does not illuminate, go to step 22).
  21. Check for an open in wire between underhood electrical center terminal J3 (Brown wire) and fan No. 2, or Black wire between fan No. 2 and ground. If a repair was made, go to step 73). If a repair was not made, go to step 59).
  22. Check for poor connection at series/parallel cooling fan relay No. 3. If a repair was made, go to step 73). If a repair was not made, go to step 67).
  23. Check for an open in Light Blue wire between underhood electrical center terminal No. D4 (Light Blue wire) and fan No. 1 or an open in Black wire between underhood electrical center terminal J4 (Black wire) and fan No. 1. If a repair was made, go to step 73). If a repair was not made, go to step 71).
  24. Using scan tool, view A/C REQUEST. If scan tool displays YES, perform clutch diagnosis. If scan tool does not display YES, go to next step.
  25. If cooling fan(s) run at low speed, go to next step. If cooling fans do not run at low speed, go to step 34).
  26. Remove low speed cooling fan relay No. 1 from underhood electrical center. If fans are on, go to step 27). If cooling fans are not on, go to step 30).
  27. If both cooling fans are running, go to next step. If both cooling fans are not running, go to step 29).
  28. Repair short to voltage in Light Blue wire. Go to step 73).
  29. Repair short to voltage in Brown wire. Go to step 73).
  30. Using a test light connected to voltage, probe terminal D2 (Dark Green wire) in underhood electrical center. If test light illuminates, go to step 32). If test light does not illuminate, go to next step.
  31. Replace low speed cooling fan relay No. 1. Go to step 73).
  32. Turn ignition off. Disconnect PCM Blue connector. Using a test light connected to voltage, probe terminal D2 (Dark Green wire) in underhood electrical center. If test light illuminates, go to next step. If test light does not illuminate, go to step 70).
  33. Repair short to ground in Dark Green wire. Go to step 73).
  34. If both fans run at high speed, go to next step. If both fans do not run at high speed, go to step 45).
  35. Using scan tool, view A/C PRESSURE SIGNAL. If scan tool display reads less than 1.2 volts, go to next step. If scan tool display reads 1.2 volts or greater, go to step 37).
  36. Repair short to ground in Dark Blue wire. Go to step 73).
  37. Turn ignition off. Disconnect A/C refrigerant pressure switch. Turn ignition on. Using scan tool, view A/C PRESSURE SIGNAL. If scan tool displays about zero volts, go to step 39). If scan tool does not display about zero volts, go to next step.
  38. Probe A/C PRESSURE SIGNAL circuit with a voltmeter connected to A/C PRESSURE SIGNAL sensor ground. If reading is about zero volts, go to step 69). If reading is not about zero volts, go to step 44).
  39. Disconnect A/C refrigerant pressure sensor. Using a test light connected to battery voltage, probe A/C refrigerant pressure sensor ground terminal. If test light illuminates, go to next step. If test light does not illuminate, go to step 42).
  40. Probe A/C refrigerant pressure sensor 5-volt reference circuit with a voltmeter connected to A/C refrigerant pressure sensor ground. If reading is about 5 volts, go to next step. If reading is not about 5 volts, go to step 43).
  41. Replace A/C refrigerant pressure sensor. Go to step 73).
  42. Locate and repair short to voltage in A/C refrigerant pressure sensor ground circuit. Go to step 73).
  43. Locate and repair open or short to ground in A/C refrigerant pressure sensor 5-volt reference circuit. Go to step 73).
  44. Locate and repair short to voltage in A/C refrigerant pressure signal circuit. Go to step 73).
  45. If fan No. 2 is running at high speed, go to step 60). If fan No. 2 is not running at high speed, go to next step.
  46. Turn ignition off. Remove fan high speed cooling fan relay No. 2 from underhood electrical center. Turn ignition on. Using a test light connected to ground, probe underhood electrical center terminal F2 (Dark Blue wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 48).
  47. Using test light connected to ground, probe underhood electrical center terminal F4 (Red wire). If test light illuminates, go to step 50). If test light does not illuminate, go to step 49).
  48. Locate and repair open in ignition feed circuit to relays. Go to step 73).
  49. Locate and repair open or short to ground in battery feed circuit to fan relays. Go to step 73).
  50. Connect test light between terminals F2 (Dark Blue wire) and F5 (Orange wire) in underhood electrical center. Turn ignition on. Using scan tool OUTPUT TESTS function, activate Fan No. 2. If test light illuminates, go to step 53). If test light does not illuminate, go to next step.
  51. Turn ignition off. Disconnect PCM Blue connector. Install a fused jumper between terminals F2 (Dark Blue wire) and F5 (Orange wire) in underhood electrical center. Turn ignition on. Probe PCM connector terminal C1-31 (Dark Blue wire) with a test light to ground. If test light illuminates, go to step 69). If test light does not illuminate, go to next step.
  52. Locate and repair open in fan No. 2 (high speed) driver circuit between PCM and underhood electrical center. Go to step 73).
  53. Turn ignition off. Install a fused jumper between terminals F1 (Brown wire) and F4 (Red wire) in underhood electrical center. If fan No. 2 is running at high speed, go to next step. If fan No. 2 is not running at high speed, go to step 55).
  54. Check for poor connection at high speed cooling fan relay No. 2. If a repair was made, go to step 73). If a repair was not made, go to step 72).
  55. Turn ignition off. Remove fused jumper between terminals F1 (Brown wire) and F4 (Red wire) in underhood electrical center. Disconnect fan No. 2 harness connector from fan motor. Install fused jumper between terminals F1 (Brown wire) and F4 (Red wire) in underhood electrical center. Using a test light connected to ground, probe terminal "B" (Brown wire) of fan No. 2 harness connector. If test light illuminates, go to step 57). If test light does not illuminate, go to next step.
  56. Locate and repair open in Brown wire between underhood electrical center terminal F1 (Brown wire) and secondary fan harness connector terminal "B" (Brown wire). Go to step 73).
  57. Disconnect secondary fan harness connector. Using a test light connected to voltage, probe terminal "B" (Brown wire) of secondary fan harness connector If test light illuminates, go to step 59). If test light does not illuminate, go to next step.
  58. Locate and repair open in Black ground wire between secondary fan harness connector terminal and ground. Go to step 73).
  59. Replace fan No. 2 motor. Go to step 73).
  60. Turn ignition off. Remove high speed cooling fan relay No. 2 from underhood electrical center. Turn ignition on. Using a test light connected to ground, probe underhood electrical center terminal F2 (Dark Blue wire). If test light illuminates, go to step 62). If test light does not illuminate, go to next step.
  61. Locate and repair open or short to ground in battery feed circuit to underhood electrical center terminal F2 (Dark Blue wire). Go to step 73).
  62. Connect a test light between terminals J1 (Black wire) and J5 (Orange wire) in underhood electrical center. Turn ignition on. If test light illuminates, go to step 64). If test light does not illuminate, go to next step.
  63. Locate and repair open in Black ground wire between underhood electrical center terminal J1 and chassis ground. Go to step 73).
  64. Turn ignition off. Install series/parallel cooling fan relay No. 3 in underhood electrical center. Remove high speed cooling fan relay No. 2 from underhood electrical center. Install fused jumper wire to ground in terminal F5 (Orange wire) of underhood electrical center. Using scan tool OUTPUT TEST function, activate fan No. 2. If fans run at high speed, go to step 68). If fans do not run at high speed, go to next step.
  65. Check for an open in Dark Blue wire between underhood electrical center terminals J2 and F5. If a repair was made, go to step 73). If a repair was not made, go to next step.
  66. Check for a faulty connection at series/parallel cooling fan relay No. 3 in underhood electrical center. If a repair was made, go to step 73). If a repair was not made, go to next step.
  67. Replace series/parallel cooling fan relay No. 3. Go to step 73).
  68. Check for an open circuit in fan No. 2 driver circuit between PCM and underhood electrical center. If a repair was made, go to step 73). If a repair was not made, go to next step.
  69. Check fan No. 1 and fan No. 2 driver circuits for a poor connection at PCM. If a repair was made, go to step 73). If a repair was not made, go to next step.
  70. Replace PCM. Go to step 73).
  71. Replace fan No. 1 motor. Go to step 73).
  72. Replace high speed cooling fan relay No. 2. Go to step 73).
  73. Ensure engine coolant temperature is less than 212°F (100°C). Turn A/C off. Start and run engine at idle. If cooling fans are running, go to step 24). If cooling fans are not running, go to next step.
  74. Using scan tool OUTPUT TESTS function, activate fan No. 1. If both fans run at low speed, go to next step. If both fans do not run at low speed, go to step 8).
  75. Using scan tool OUTPUT TESTS function, activate fan No. 2. If both fans run at high speed after 6 seconds, repair is complete. If both fans do not run at high speed after 6 seconds, go to step 34).
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