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Engine Control System - System/component Tests: Diagnosis Oldsmobile Silhouette II

Testing & Diagnostics ~5824 words

A/C ON SWITCH/SYSTEM TEST

  1. Turn ignition switch to RUN position. Move mode selector switch to any position other than OFF position. With A/C control assembly connected, measure voltage between mode selector switch Light Dark Green/White wire and ground. For wiring schematics, see the WIRING DIAGRAMS article.
  2. Battery voltage should be present. If battery voltage is present, mode selector switch is operating normally. If battery voltage is not present, check wire from mode selector switch to fuse for an open circuit. Also check A/C high and low pressure switches for open.
  3. Check voltage between mode selector switch Dark Green/White wire or Light Green wire and ground. Voltage should not be present. If voltage is present, replace mode selector switch.

Port Fuel Injector Balance Test (SFI)

The injector balance test is used to pulse the injector for a precise amount of time, spraying a measured amount of fuel in the intake manifold. As each injector is pulsed, a drop in fuel rail pressure occurs. This pressure drop can be recorded and compared to other injectors. All injectors should have a pressure drop of 1.5 psi (.11 kg/cm 2 ) or less. If pressure drop is more or less than other injectors, replace appropriate injector.

Note. Allow engine to cool to avoid irregular readings due to "hot soak" fuel boiling. To prevent flooding, INJECTOR BALANCE TEST should not be repeated more than once without starting and running engine.

  1. Turn ignition off. Connect Fuel Pressure Gauge (J-39021-301) to pressure tap. Unplug harness connector at all injectors. Connect Injector Switch Box (J-39021-210) to one of the injectors.
  2. Follow manufacturer's instructions when installing adapter harness. Ignition should be turned off at least 10 seconds to complete PCM/VCM shutdown cycle.
  3. Turn ignition on. Fuel pump should run at least 2 seconds after ignition is turned on. Bleed air from gauge and hose to ensure accurate gauge reading. Repeat this procedure until all air is bled from system. Turn ignition off for at least 10 seconds.
  4. Turn ignition on again to bring fuel pressure to maximum. Record initial pressure reading. Energize switch box one time and note pressure drop at lowest point.
  5. Disregard any slight pressure drop after low point is reached. Subtracting second pressure reading from initial reading indicates amount of injector pressure drop.
  6. Repeat step 4) on each injector and compare pressure drop. Recheck injectors not within pressure drop range. Replace injector(s) failing second check. If injectors are all okay, plug in harness connectors and review SYMPTOMS in the «TESTS W/O CODES»(ref-20617) article.

Warning Light Diagnosis

  1. Perform On-Board Diagnostics (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the «BASIC TESTING»(ref-20674) article. After performing OBD system check, go to next step.
  2. Check instrument cluster. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section. If instrument panel is okay, go to next step.
  3. Turn ignition off. Disconnect PCM connector. Turn ignition on. Using a DVOM, check voltage between affected PCM output circuit at PCM harness connector terminal and ground. See the WIRING DIAGRAMS article. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 7).
  4. Set DVOM to 10-amp scale. Check current between affected PCM output circuit and ground. Monitor reading for about 2 minutes. DVOM should read .05-1.50 amps. If reading is as specified, go to step 12). If reading is not as specified, go to next step.
  5. Disconnect instrument cluster, leaving PCM connector disconnected. Using DVOM, check voltage between affected PCM output circuit and ground. DVOM should read zero volts. If voltage reading is as specified, go to step 15). If voltage reading is not as specified, go to next step.
  6. Locate and repair short to voltage in affected PCM output circuit. After repairs, go to step 17).
  7. Check ignition feed fuse for instrument cluster indicator lights. If fuse is blown, go to next step. If fuse is okay, go to step 9).
  8. Locate and repair short to ground in ignition feed circuit for instrument cluster indicator lights. Replace fuse and go to step 17).
  9. Disconnect instrument cluster connector. Turn ignition on. Check voltage between ignition feed circuit for instrument cluster indicator lights and ground. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 14).
  10. Check affected PCM output circuit for an open or shorted circuit to ground. If circuit is open or shorted, go to step 17). If circuit was okay, go to next step.
  11. Check affected PCM output circuit and ignition feed circuit for poor connection at instrument cluster and at PCM. If problem is present, repair as necessary and then go to step 17). If problem was not found, go to step 15).
  12. Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect a test light between affected PCM output circuit and ignition feed circuit at instrument panel harness connector. Using a scan tool, perform OUTPUTS TEST function to cycle affected warning light on and off. If test light flashes on and off, check for shorted component or circuit in the output driver circuit. Check for faulty instrument cluster. If test light does not flash on and off, go to next step.
  13. Check affected PCM output circuit for poor connection to PCM. Replace defective terminal and then go to step 17). If terminal is okay, go to step 16).
  14. Repair open in ignition feed circuit to instrument cluster indicator lights. After repairs, go to step 17).
  15. Replace instrument cluster and then go to step 17).
  16. Replace PCM and then go to next step.
  17. Using scan tool, operate affected warning light. If warning light does not operate properly, go to step 3).

Tachometer Control Circuit Diagnosis

  1. Diagnose instrument cluster. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section. After diagnosis, go to next step.
  2. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the «BASIC TESTING»(ref-20674) article. After performing OBD system check, go to next step.
  3. Turn ignition off. Disconnect PCM connector. Turn ignition on. Using a DVOM, check voltage between tachometer control circuit at PCM harness connector terminal and ground. See the WIRING DIAGRAMS article. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 7).
  4. Set DVOM to 10-amp scale. Check current between tachometer control circuit and ground. Monitor reading for about 2 minutes. DVOM should read .05-1.50 amps. If reading is not as specified, go to next step. If reading is as specified, go to step 12).
  5. Disconnect instrument cluster, leaving PCM connector disconnected. Using DVOM, check voltage between tachometer control circuit and ground. DVOM should read zero volts. If voltage reading is as specified, go to step 15). If voltage reading is not as specified, go to next step.
  6. Locate and repair short to voltage in tachometer control circuit. After repairs, go to step 17).
  7. Check ignition feed fuse for instrument cluster. If fuse is blown, go to next step. If fuse is okay, go to step 9).
  8. Locate and repair short to ground in ignition feed circuit to instrument cluster. Replace fuse and go to step 17).
  9. Disconnect instrument cluster connector. Turn ignition on. Check voltage between ignition feed circuit for instrument cluster and ground. Battery voltage should be present. If battery voltage was not present, go to step 14). If battery voltage is present, go to next step.
  10. Check tachometer control circuit for an open or shorted circuit to ground. If circuit is open or shorted, go to step 17). If circuit was okay, go to next step.
  11. Check tachometer control circuit and ignition feed circuit for poor connection at instrument cluster and at PCM. If problem is present, repair as necessary and then go to step 17). If problem was not found, go to step 15).
  12. Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect a test light between tachometer control circuit and ignition feed circuit at instrument panel harness connector. Using a scan tool, perform OUTPUTS TEST function to cycle tachometer control output light on and off. If test light flashes on and off, check for shorted component or circuit in the output driver circuit. Check for faulty instrument cluster. If test light does flash on and off, go to next step.
  13. Check tachometer control circuit for poor connection to PCM. Replace defective terminal and then go to step 17). If terminal is okay, go to step 16).
  14. Repair open in ignition feed circuit to instrument cluster. After repairs, go to step 17).
  15. Replace instrument cluster and then go to step 17).
  16. Replace PCM and then go to next step.
  17. Start engine and observe tachometer. If tachometer does not operate properly, diagnose instrument cluster. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section.

Compressor Clutch Control Circuit Diagnosis

  1. If On-Board Diagnostic (OBD) System Check has not been performed, see the «BASIC TESTING»(ref-20674) article and go to OBD SYSTEM CHECK. If OBD SYSTEM CHECK has been performed, go to next step.
  2. Check for any DTCs that may be set. If any DTCs are set, perform diagnosis for that DTC first. See the «TESTS W/CODES»(ref-20678) article. If no DTCs are set, go to next step.
  3. Ensure intake air temperature is greater than 60°F (15°C). Ensure engine coolant temperature is less than 246°F (119°C). Turn A/C off. Start engine and let idle. Observe A/C compressor clutch. If A/C compressor clutch is engaged, go to step 21). If A/C compressor clutch is not engaged, go to next step.
  4. Run engine at 1000-1500 RPM. Select DEFROST or MAX mode on A/C control head. Observe A/C compressor clutch. If A/C compressor clutch is engaged, system is operating correctly. Problem may be intermittent. If A/C compressor clutch is not engaged, go to next step.
  5. With DEFROST or MAX mode still selected, observe A/C REQUEST display on scan tool. If A/C REQUEST displays YES, go to step 9). If A/C REQUEST does not display YES, go to next step.
  6. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. With DEFROST or MAX mode still selected, use a voltmeter and measure voltage on A/C request circuit (Dark Green/White wire) at PCM harness connector. If reading is near battery voltage, go to step 8). If reading is not as specified, go to next step.
  7. Check A/C request circuit (Dark Green/White wire) for an open, short to ground, or poor connection at A/C control head. Repair as necessary. Go to step 37). If no problem is found, diagnose A/C controls.
  8. Check A/C request circuit (Dark Green/White wire) for a poor connection at PCM. Repair as necessary. Go to step 37). If no problem is found, go to step 35).
  9. Observe A/C refrigerant pressure sensor display on scan tool. If reading is .35-4.27 volts, go to step 12). If reading is not as specified, go to next step.
  10. Install A/C manifold gauge set. Observe high-side refrigerant pressure on gauge. If high-side refrigerant pressure is 34-414 psi (2.3-29 kg/cm 2 ), go to next step. If high-side refrigerant pressure is not as specified, charge A/C system using approved A/C refrigerant recovery/recycling equipment. Go to step 37).
  11. Turn ignition off. Disconnect PCM and A/C refrigerant pressure sensor. Using an ohmmeter, measure resistance of following circuits between PCM and A/C refrigerant pressure sensor harness connectors: Refrigerant pressure sensor signal circuit (Red/Black wire). 5-volt reference "B" circuit (Gray wire). Sensor ground circuit (Black wire). If any resistance is greater than 5 ohms, locate and repair cause of high resistance in circuit as necessary, then go to step 37). If any resistance is not greater than 5 ohms, go to step 18).
  12. Disconnect A/C relay harness connector. Using a test light connected to ground, probe ignition feed circuits (Pink wires) at A/C relay harness connector. If test light comes on, go to next step. If test light does not come on, go to step 31).
  13. Connect a fused jumper between ignition feed circuit and A/C compressor clutch ignition feed circuit (Dark Green wire) at A/C relay connector. If A/C compressor clutch engages, go to step 14). If A/C compressor clutch does not engage, leave jumper wire in place and go to step 15).
  14. Check for poor connections at A/C relay. Repair as necessary. Go to step 37). If no problem is found, go to step 32).
  15. Disconnect A/C compressor clutch harness connector. Connect a test light between A/C compressor clutch ignition feed circuit (Dark Green wire) and A/C compressor clutch ground circuit (Black wire). If test light comes on, go to next step. If test light does not come on, go to step 17).
  16. Check for poor connections at A/C compressor clutch. Repair as necessary. Go to step 37). If no problem is found, go to step 33).
  17. Check for an open or short to ground in A/C compressor clutch ignition feed circuit (Dark Green wire). Repair as necessary. After repairs, go to step 37). If no problem is found, go to step 34).
  18. Leave PCM and A/C refrigerant pressure sensor disconnected at PCM. Turn ignition on. Using a voltmeter, measure voltage between A/C refrigerant pressure signal circuit (Red/Black wire) and ground. If reading is near zero volts, go to next step. If reading is not as specified, go to step 20).
  19. Check for the following conditions: 5-volt reference "B" circuit (Gray wire) for a poor connection at PCM. 5-volt reference "B" circuit (Gray wire) for a poor connection at refrigerant pressure sensor. Refrigerant pressure signal circuit (Red/Black wire) for a poor connection at PCM. Refrigerant pressure signal circuit (Red/Black wire) for a poor connection at refrigerant pressure sensor. Sensor ground circuit (Black wire) for a poor connection at refrigerant pressure sensor. Repair as necessary and go to step 37). If no problem is found, go to step 36).
  20. Locate and repair short to power in A/C refrigerant pressure signal circuit (Red/Black wire). Go to step 37).
  21. Turn ignition on. Turn A/C off. Observe A/C REQUEST on scan tool. If A/C REQUEST displays YES, go to next step. If A/C REQUEST does not display YES, go to step 24).
  22. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on, A/C off. Using a voltmeter, measure voltage between ground and PCM harness connector C1, terminal No. 62 (A/C request circuit). If reading is near battery voltage, go to next step. If reading is not as specified, go to step 35).
  23. Turn ignition off. Disconnect A/C control head/programmer. Turn ignition on. Check A/C request circuit for a short to power. Repair as necessary. Go to step 37). If no problem is found, diagnose A/C controls.
  24. Disconnect A/C relay. Start engine and observe A/C compressor clutch. If A/C compressor clutch is engaged, go to step 29). If A/C compressor clutch is not engaged, go to next step.
  25. Using a test light connected to ground, probe A/C compressor clutch ignition feed circuit (Dark Green wire) at A/C relay harness connector. If test light comes on, go to step 27). If test light does not come on, go to next step.
  26. Replace A/C relay. Go to step 37).
  27. Turn ignition off. Disconnect PCM harness connector C1. Using a test light connected to battery voltage, probe A/C relay driver circuit (Dark Green/White wire) at PCM connector. If test light comes on, go to next step. If test light does not come on, go to step 35).
  28. Repair short to ground in A/C compressor clutch relay driver circuit (Dark Green/White wire). Go to step 37).
  29. Turn ignition off. Disconnect A/C compressor clutch harness connector. Start engine and observe A/C compressor clutch. If A/C compressor clutch is engaged, go to step 33). If A/C compressor clutch is not engaged, go to next step.
  30. Locate and repair short to power in A/C compressor clutch ignition feed circuit (Dark Green wire). Go to step 37).
  31. Repair open or short to ground in ignition feed circuit (Pink wire) to A/C compressor relay. Go to step 37).
  32. Replace A/C compressor relay. Go to step 37).
  33. Repair A/C compressor clutch. Go to step 37).
  34. Locate and repair open in A/C compressor clutch ground circuit (Black wire). Go to step 37).
  35. Replace PCM. Go to step 37).
  36. Replace A/C refrigerant pressure sensor. Go to step 37).
  37. Ensure intake air temperature is greater than 60°F (15°C). Ensure engine coolant temperature is less than 246°F (119°C). With A/C off, start engine and let idle. Observe A/C compressor clutch. If A/C compressor clutch is engaged, go to step 21). If A/C compressor clutch is not engaged, go to next step.
  38. Run engine at 1000-1500 RPM. Select DEFROST or MAX mode on control head. Observe A/C compressor clutch. If A/C compressor clutch is engaged, system is okay. If A/C compressor clutch is not engaged, go to step 5).

ELECTRIC COOLING FAN CIRCUIT DIAGNOSIS

Note. Cooling fan circuit utilizes 3 cooling fan relays. Relays directly controlling fan motors are 4-pin type and are referred to as No. 1 and No. 2. Relay determining cooling fan motor low speed or high speed operation is referred to as 5-pin relay in this test. See WIRING DIAGRAM .

Cooling Fan Circuit Diagnosis

  1. If Powertrain On-Board Diagnostic (OBD) System Check has not been performed, see the «BASIC TESTING»(ref-20674) article and go to OBD SYSTEM CHECK. If OBD SYSTEM CHECK has been performed, go to next step.
  2. Check for PCM Diagnostic Trouble Codes (DTCs). If any DTCs are present, perform testing for applicable DTC. Repair all DTCs that are set before proceeding with testing. See the «TESTS W/CODES»(ref-20678) article. If no DTCs 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 32).
  4. Using scan tool, select RELAY CONTROL function. Command low speed fans on. If cooling fans operate at low speed, go to next step. If cooling fans do not operate as specified, go to step 8).
  5. Command high speed fans on. Wait 6 seconds. If cooling fans operate at high speed, go to next step. If cooling fans do not operate as specified, go to step 58). NOTE: Ensure ambient temperature is greater than 48°F (9°C) before proceeding.
  6. Exit scan tool OUTPUT TESTS. Start engine. Turn A/C on. If cooling fans come on, go to DIAGNOSTIC AIDS. If cooling fans do not come on, go to next step.
  7. Using scan tool, view A/C REQUEST on display. If YES is displayed, go to step 77). If YES is not displayed, go to A/C CLUTCH CIRCUIT DIAGNOSIS TEST in «A/C COMPRESSOR CLUTCH CONTROLS»(ref-20675-S07940623862001010300000) .
  8. If either cooling fan is running, go to next step. If neither cooling fan runs, go to step 16).
  9. If cooling fan No. 1 runs, go to next step. If cooling fan No. 1 does not run, go to step 14).
  10. Turn ignition off. Disconnect cooling fan No. 2 harness connector. Turn ignition on. Using scan tool, select RELAY CONTROL function. Command low speed fans on. If cooling fan No. 1 runs, go to next step. If cooling fan No. 1 does not run, go to step 80).
  11. Remove cooling fan relay (5-pin) from underhood electrical center. If cooling fan No. 1 runs, go to next step. If cooling fan No. 1 does not run, go to step 13).
  12. Locate and repair short to ground in circuit No. 532 (Gray wire). Go to step 81).
  13. Check circuit No. 409 (Light Blue wire), and/or circuit No. 473 (Dark Blue wire) for a short to ground. Repair as necessary. After repairs, go to step 81). If no problem was found, go to step 70).
  14. Turn ignition off. Disconnect cooling fan No. 1 harness connector. Turn ignition on. Using scan tool, select RELAY CONTROL function. Command low speed fans on. If cooling fan No. 2 runs, go to next step. If cooling fan No. 2 does not run, go to step 71).
  15. Replace cooling fan No. 1 diode. Go to step 81).
  16. Turn ignition on. Remove No. 1 cooling fan relay from underhood electrical center. Using a test light connected to ground, probe No. 1 cooling fan relay cavity No. 87. If test light comes on, go to step 18). If test light does not come on, go to next step.
  17. Check for blown Maxi-fuse that supplies power to No. 1 cooling fan relay. If fuse is blown, locate and repair short circuit. Possible causes for short circuit are: Seized cooling fan motors. Shorted cooling fan motor windings. Short to ground in circuit No. 504. Short to ground in power feed circuit between fuse and No. 1 cooling fan relay. If fuse is not blown, check for an open in power feed circuit between fuse and No. 1 cooling fan relay. Repair as necessary. Go to step 81).
  18. Using a test light connected to ground, probe No. 1 cooling fan relay cavity No. 86. If test light comes on, go to step 20). If test light does not come on, go to next step.
  19. Check for blown Maxi-fuse that supplies power to No. 1 cooling fan relay. If fuse is blown, locate and repair short circuit. Possible causes for short circuit are: Seized cooling fan motors. Shorted cooling fan motor windings. Short to ground in circuit No. 504. Shorted relay coil in cooling fan relay. Short to ground in power feed circuit between fuse and No. 1 cooling fan relay. If fuse is not blown, check for an open in power feed circuit between fuse and No. 1 cooling fan relay. Repair as necessary. Go to step 81).
  20. Turn ignition off. Disconnect both cooling fan harness connectors. Using fused jumper wires, jumper terminals "A" and "B" together at both harness connectors. Turn ignition on. Connect a test light between No. 1 cooling fan relay cavities No. 30 and 87. If test light comes on, go to next step. If test light does not come on, go to step 27).
  21. Connect a test light between No. 1 cooling fan relay cavities No. 85 and 86. Turn ignition on. Using scan tool, select RELAY CONTROL function. Command low speed fans on. If test light comes on, go to next step. If test light does not come on, go to step 25).
  22. Turn ignition off. Remove jumper wires and reconnect cooling fan harness connectors. Connect a fused jumper wire between No. 1 cooling fan relay cavities No. 30 and 87. Turn ignition on. If both cooling fans run, go to next step. If both cooling fans do not run, go to step 24).
  23. Check for poor connections at No. 1 cooling fan relay in underhood electrical center. Repair as necessary. Go to step 81). If no problem was found, go to step 37).
  24. Check for poor connections at both cooling fan motors. Repair as necessary. Go to step 81). If no problem was found, go to step 63).
  25. Turn ignition off. Disconnect PCM harness connector C1. Install a fused jumper wire between No. 1 cooling fan relay cavities No. 85 and 86. Turn ignition on. Using a test light connected to ground, probe PCM harness connector C1, terminal No. 32 (Dark Green wire). If test light comes on, go to step 77). If test light does not come on, go to next step.
  26. Locate and repair open in circuit No. 335 (Dark Green wire) between No. 1 cooling fan relay and PCM harness connector C1, terminal No. 32. Go to step 81).
  27. Turn ignition off. Remove jumper wires and reconnect cooling fan harness connectors. Connect a fused jumper wire between No. 1 cooling fan relay cavities No. 30 and 87. Remove cooling fan relay (5-pin) from underhood electrical center. Using a test light connected to ground, probe cooling fan relay (5-pin) cavity No. 30. If test light comes on, go to next step. If test light does not come on, go to step 31).
  28. Connect a test light between cooling fan relay (5-pin) cavities No. 30 and 87A. If test light comes on, go to step 30). If test light does not come on, go to next step.
  29. Check for open in circuit No. 409 (Light Blue wire) between cooling fan relay (5-pin) cavity No. 87A and harness connector terminal "B" at cooling fan motor No. 2. Repair as necessary. Go to step 81). If no problem was found, go to step 57).
  30. Check for poor connections at cooling fan relay (5-pin) cavities No. 30 and 87A in underhood electrical center. Repair as necessary. Go to step 81). If no problem was found, go to step 76).
  31. Check for an open in circuit No. 504 (White wire) between No. 1 cooling fan relay cavity No. 30 and harness connector terminal "B" at cooling fan motor No. 1. Repair as necessary. Go to step 81). If no problem was found, go to step 56).
  32. Using scan tool, view A/C REQUEST on display. If YES is displayed, go to appropriate A/C CLUTCH CIRCUIT DIAGNOSIS TEST in «A/C COMPRESSOR CLUTCH CONTROLS»(ref-20675-S07940623862001010300000) . If YES is not displayed, go to next step.
  33. If both cooling fans are operating at low speed, go to next step. If both cooling fans do not operate at low speed, go to step 40).
  34. Remove No. 1 cooling fan relay from underhood electrical center. If both cooling fans run, go to next step. If both cooling fans do not run, go to step 36).
  35. Locate and repair short to power in circuit No. 504 (White wire). Go to step 81).
  36. Using a test light connected to battery positive, probe No. 1 cooling fan relay cavity No. 85. If test light comes on, go to step 38). If test light does not come on, go to next step.
  37. Replace No. 1 cooling fan relay. Go to step 81).
  38. Turn ignition off. Disconnect PCM harness connector C1. Using a test light connected to battery positive, probe No. 1 cooling fan relay cavity No. 85. If test light come on, go to next step. If test light does not come on, go to step 77).
  39. Locate and repair short to ground in circuit No. 335 (Dark Green wire) between No. 1 cooling fan relay and PCM harness connector C1, terminal No. 32. Go to step 81).
  40. If both cooling fans operate at high speed, go to next step. If both cooling fans do not operate at high speed, go to step 42).
  41. Using scan tool, view A/C PRESSURE on display. If reading is less than 1.2 volts, go to step 77). If reading is 1.2 volts or greater, go to step 44).
  42. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on. If cooling fan No. 2 operates at high speed, go to next step. If cooling fan No. 2 does not operate at high speed, go to step 77).
  43. Check for a short to ground in circuit No. 473 to cooling fan relay (5-pin) and relay No. 2 control circuit (Dark Blue wire). Repair as necessary. Go to step 81). If no problem was found, go to step 52).
  44. Turn ignition off. Disconnect A/C pressure sensor harness connector. Turn ignition on. Using scan tool, view A/C PRESSURE on display. If reading is near zero volts, go to step 46). If reading is not as specified, go to next step.
  45. Using a voltmeter, measure voltage between A/C pressure sensor signal and ground circuits. If reading is near zero volts, go to step 77). If reading is not as specified, go to step 51).
  46. Using a test light connected to battery positive, probe A/C pressure sensor ground circuit. If test light comes on, go to next step. If test light does not come on, go to step 49).
  47. Using a voltmeter, measure voltage between A/C pressure sensor 5-volt reference and sensor ground. If reading is near 5 volts, go to next step. If reading is not as specified, go to step 50).
  48. Replace A/C pressure sensor. Go to step 81).
  49. Locate and repair open or short to power in A/C pressure sensor ground circuit. Go to step 81).
  50. Locate and repair open or short to ground in A/C pressure sensor 5-volt reference circuit. Go to step 81).
  51. Locate and repair short to power in A/C pressure sensor signal circuit. Go to step 81).
  52. Remove No. 2 cooling fan relay from underhood electrical center. If cooling fan No. 2 operates at high speed, go to next step. If cooling fan No. 2 does not operate at high speed, go to step 70).
  53. Remove cooling fan relay (5-pin) from underhood electrical center. If cooling fan No. 2 operates at high speed, go to next step. If cooling fan No. 2 does not operate at high speed, go to step 55).
  54. Locate and repair short to power in circuit No. 409 (Light Blue wire) between No. 2 cooling fan relay and cooling fan motor No. 2. Go to step 81).
  55. Locate and repair short to power in circuit No. 532 (Dark Blue wire) between cooling fan relay (5-pin) and cooling fan motor No. 1. Go to step 81).
  56. Check for an open in circuit No. 532 (Dark Blue wire) between cooling fan relay (5-pin) cavity No. 30 and terminal "A" of cooling fan motor No. 1 harness connector. Repair as necessary. Go to step 81). If no problem was found, go to step 79).
  57. Check for an open in circuit No. 1050 (Black wire) between cooling fan motor No. 2 harness connector terminal "A" and ground. Repair as necessary. Go to step 81). If no problem was found, go to step 80).
  58. Turn ignition on. Remove No. 2 cooling fan relay from underhood electrical center. Connect a test light between No. 2 cooling fan relay cavity No. 86 and battery positive. Using scan tool, select RELAY CONTROL function. Command high speed fans on. Wait 6 seconds. If test light comes on, go to step 61). If test light does not come on, go to next step.
  59. Remove cooling fan relay (5-pin) from underhood electrical center. Connect a test light between cooling fan relay (5-pin) cavity No. 86 and battery positive. Using scan tool, select RELAY CONTROL function. Command high speed fans on. Wait 6 seconds. If test light comes on, go to step 78). If test light does not come on, go to next step.
  60. Turn ignition off. Disconnect PCM harness connector C1. Check circuit No. 473 (Dark Blue wire) for an open or short to power. Repair as necessary. Go to step 81). If no problem is found, go to step 77).
  61. Turn ignition off. Reinstall No. 2 cooling fan relay. Disconnect both cooling fan motor harness connectors. Turn ignition on. Using scan tool, select RELAY CONTROL function. Command high speed fans on. Wait 6 seconds. Using a test light connected to ground, probe terminal "B" of cooling fan motor No. 2 harness connector. If test light comes on, go to next step. If test light does not come on, go to step 64).
  62. Using a test light connected to battery positive, probe terminal "A" of cooling fan motor No. 1 harness connector. If test light comes on, go to next step. If test light does not come on, go to step 71).
  63. Check for a seized cooling fan motor or open motor winding. Replace appropriate cooling fan motor. Go to step 81).
  64. Turn ignition off. Remove No. 2 cooling fan relay from underhood electrical center. Turn ignition on. Using a test light connected to ground, probe No. 2 cooling fan relay cavity No. 85. If test light comes on, go to step 66). If test light does not come on, go to next step.
  65. Locate and repair open in battery positive circuit to No. 2 cooling fan relay. Check for blown Maxi-fuse (30-amp). Repair short to ground if blown. Replace fuse. Go to step 81).
  66. Using a test light connected to ground, probe No. 2 cooling fan relay cavity No. 30. If test light comes on, go to step 68). If test light does not come on, go to next step.
  67. Locate and repair open in battery positive circuit to No. 2 cooling fan relay cavity No. 30. Go to step 81).
  68. Check for open in circuit No. 409 (Light Blue wire) between cooling fan motor No. 2 harness connector terminal "B" and No. 2 cooling fan relay cavity No. 87. Repair as necessary. Go to step 81). If no problem was found, go to next step.
  69. Check for poor connections at No. 2 cooling fan relay in underhood electrical center. Repair as necessary. Go to step 81). If no problem was found, go to next step.
  70. Replace No. 2 cooling fan relay. Go to step 81).
  71. Turn ignition off. Remove cooling fan relay (5-pin) from underhood electrical center. Turn ignition on. Using a test light connected to ground, probe cooling fan relay (5-pin) cavity No. 85. If test light comes on, go to step 73). If test light does not come on, go to next step.
  72. Locate and repair open in battery positive circuit to cooling fan relay (5-pin) cavity No. 85. Go to step 81).
  73. Using a test light connected to battery positive, probe cooling fan relay (5-pin) cavity No. 87. If test light comes on, go to step 75). If test light does not come on, go to next step.
  74. Locate and repair open in circuit No. 1050 (Black wire) between cooling fan relay (5-pin) cavity No. 87 and ground. Go to step 81).
  75. Check for poor connections at cooling fan relay (5-pin) in underhood electrical center. Repair as necessary. Go to step 81). If no problem was found, go to step 76).
  76. Replace cooling fan relay (5-pin). Go to step 81).
  77. Replace PCM. Go to step 81).
  78. Repair open in circuit No. 473 (Dark Blue wire) between PCM harness connector C1, terminal No. 31 and cooling fan relays (5-pin and No. 2) cavity No. 86. Go to step 81).
  79. Replace cooling fan motor No. 1. Go to step 81).
  80. Replace cooling fan motor No. 2. Go to step 81).
  81. Ensure coolant temperature is less than 212°F (100°C). Turn A/C off. Start engine and let idle. If cooling fans are running, go to step 32). If cooling fans are not running, go to next step.
  82. Using scan tool, select RELAY CONTROL function. Command low speed fans on. If both cooling fans operate at low speed, go to next step. If both cooling fans do not operate at low speed, go to step 8).
  83. Command high speed cooling fans on. Wait 6 seconds. If both cooling fans operate at high speed, system is okay at this time. If both cooling fans do not operate at high speed, go to step 58).

Diagnostic Aids

Check for poor connections at PCM, cooling fan relays and cooling fan motors. Inspect harness connectors for damaged, corroded or backed-out terminal pins. Inspect related wiring harnesses for damage or improper routing.

More articles — Engine Control System - System/component Tests