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Home >> Oldsmobile >> 1996 >> Eighty-Eight LS >> 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 for PCM Diagnostic Trouble Codes (DTCs). If any codes are present, perform testing for applicable code. Some DTCs will cause fans to come on at all times, so 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 coolant temperature is less than 212°F (100°C). Turn A/C off. Ensure engine is running. If cooling fans are running, go to step 30). If cooling fans are not running, go to next step.
  4. Using scan tool OUTPUT TESTS, command fan No. 1 on. 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, command fan No. 2 on. If left fan runs at high speed, go to next step. If left fan does not run at high speed, go to step 18).
  6. Ensure ambient temperature is greater than 60°F (15°C). Exit scan tool output tests. Turn engine on and leave running. Turn A/C on. If fans come on, system is operating properly, but problem may be intermittent. If fans do not come on, go to next step.
  7. Using scan tool, display A/C REQUEST. If scan tool displays YES, go to step 44). If scan tool displays NO, check A/C clutch for problem.
  8. Disconnect low speed cooling fan relay. Turn ignition on. Probe low speed cooling fan relay harness connector terminal No. 85 (Brown wire) with a test light connected to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 28).
  9. Probe low speed cooling fan relay harness connector terminal No. 30 (Red wire) with a test light to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 29).
  10. Connect fused jumper between low speed cooling fan relay harness connector terminals No. 87 (Light Blue wire) and No. 30 (Red wire). If both cooling fans run at low speed, go to next step. If both cooling fans do not run at low speed, go to step 14).
  11. Using scan tool OUTPUT CONTROL function, select fan No. 1 and command fans on. Probe low speed cooling fan harness connector terminal No. 86 (Dark Green wire) with a test light to voltage. If test light illuminates, go to step 40). If test light does not illuminate, go to step 12).
  12. Turn ignition off. Disconnect PCM. Turn ignition on. Check low speed cooling fan relay driver circuit for an open or short to voltage between PCM and low speed cooling fan relay. If a problem is found, repair as necessary, then go to step 46). If a problem is not found, go to next step.
  13. Check low speed cooling fan relay driver circuit for a poor terminal connection at PCM. If a problem is found, repair as necessary, then go to step 46). If a problem is not found, go to step 44).
  14. Disconnect both cooling fan motors. Leave low speed cooling fan relay connector terminals No. 87 and 30 jumpered. Probe terminal "B" (Black or Light Blue wire) at both fan motor connectors with a test light to ground. If test light illuminates at both fan connectors, go to step 45). If test light does not illuminate at both fan connectors, go to step 16).
  15. Connect test light between terminals "A" (Light Blue or Black wire) and "B" (Light Blue or Black wire) at both cooling fan connectors. If test light illuminates at both fan connectors, go to step 45). If test light does not illuminate at both fan connectors, go to step 17).
  16. Locate and repair open circuit in Black or Light Blue wire. Go to step 46).
  17. Locate and repair open in ground circuit to affected cooling fan motors(s). Go to step 46).
  18. Disconnect high speed cooling fan relay. Turn ignition on. Probe high speed cooling fan relay harness connector terminal No. 30 (Red wire) with a test light to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 29).
  19. Probe high speed cooling fan relay harness connector terminal No. 86 (Dark Blue wire) with a test light to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 28).
  20. Connect fused jumper between high speed cooling fan relay harness connector terminals No. 30 (Red wire) and No. 87 (Black wire). If left cooling fan runs at high speed, go to next step. If left cooling fan does not run at high speed, go to step 24).
  21. Using scan tool OUTPUT CONTROL function, select fan No. 2 and command fan on. Probe high speed cooling fan harness connector terminal No. 86 (Dark Blue wire) with a test light to voltage. If test light illuminates, go to step 42). If test light does not illuminate, go to next step.
  22. Turn ignition off. Disconnect PCM. Turn ignition on. Check high speed cooling fan relay driver circuit for an open or short to voltage between PCM and high speed cooling fan relay. If a problem is found, repair as necessary, then go to step 46). If a problem is not found, go to next step.
  23. Check high speed cooling fan relay driver circuit for a poor terminal connection at PCM. If a problem is found, repair as necessary, then go to step 46). If a problem is not found, go to step 44).
  24. Disconnect left side cooling fan motor connector (leave high speed cooling fan relay harness connector terminals No. 30 and 87 jumpered). Probe left side cooling fan motor harness connector terminal "B" (Black wire) with a test light to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 27).
  25. Connect test light between left side cooling fan motor harness connector terminals "A" and "B" (Black and Light Blue wires). If test light illuminates, go to step 45). If test light does not illuminate, go to next step.
  26. Locate and repair open in ground circuit to left side cooling fan motor. Repair as necessary, then go to step 46).
  27. Locate and repair open in Black wire to left side cooling fan. Go to step 46).
  28. Locate and repair open in ignition feed circuit (Brown wire) to left side cooling fan. Go to step 46).
  29. Locate and repair open in battery feed circuit (Red wire) to affected cooling fan relay. Go to step 46).
  30. Disconnect high speed cooling fan relay. If either cooling fan is on, go to step 35). If either cooling fan is not on. go to step 31).
  31. Probe high speed cooling fan relay harness connector terminal No. 86 (Dark Blue wire) with a test light to voltage. If test light illuminates, go to next step. If test light is not illuminated, go to step 43).
  32. Observe A/C refrigerant pressure on scan tool. If A/C refrigerant pressure is greater than 260 psi (18.2 kg/cm2 ), problem is with A/C system. Diagnose A/C-heater system. If pressure is less than 260 psi (18.2 kg/cm2 ), go to next step.
  33. Turn ignition off. Disconnect PCM. Turn ignition on. Probe high speed cooling fan relay harness connector terminal No. 86 (Dark Blue wire) to voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 44).
  34. Locate and repair short to ground in high speed cooling fan relay driver circuit. Go to step 46).
  35. Disconnect low speed cooling fan relay. If either cooling fan is on, go to step 39). If either cooling fan is not on, go to step 36).
  36. Probe low speed cooling fan relay harness connector terminal No. 86 (Dark Green wire) with a test light to voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 41).
  37. Turn ignition off. Disconnect PCM. Turn ignition on. Probe low speed cooling fan relay harness connector terminal No. 86 (Dark Green wire) with a test light to voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 44).
  38. Locate and repair short to ground in low speed cooling fan relay driver circuit. Go to step 46).
  39. Locate and repair short to voltage in affected cooling fan feed circuit. (Light Blue or Black wire). Go to step 46).
  40. Check for poor connection at low speed cooling fan relay. If problem is found, repair as necessary, then go to step 46). If a problem is not found, go to step 43).
  41. Replace high speed cooling fan relay. Go to step 46).
  42. Check for poor connection at high speed cooling fan relay. If a problem is found, repair as necessary, then go to step 46). If a problem is not found, go to next step.
  43. Replace high speed cooling fan relay. Go to step 46).
  44. Replace PCM. Go to step 46).
  45. Replace affected cooling fan motor. Go to step 46).
  46. Ensure engine coolant temperature is less than 212°F (100°C). Turn A/C off. Leave engine running. If cooling fans operate, go to step 30). If cooling fans do not operate, go to next step.
  47. Using scan tool OUTPUT TESTS, command fan No. 1 on. If both fans run at low speed, go to step 48). If both fans do not run at low speed, go to step 8).
  48. Using scan tool OUTPUT TESTS, command fan No. 2 on. If left side fan runs at high speed, system is operating normally at this time. If left side fan does not run at high speed, go to step 18).
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