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Engine Control System & Engine Component Tests - 3.8L: Diagnosis Pontiac Firebird IV

Testing & Diagnostics ~5638 words

A/C ON (A/C REQUEST) SWITCH TEST

  1. Start engine and allow to idle. If a scan tool is available, scan A/C request parameter. Slide mode selector for A/C back and forth between ON and OFF positions. Scan status should change.
  2. If scan tool is not available or scan status does not change, measure voltage between ground and PCM A/C request terminal. For wiring schematics, see appropriate diagram in the WIRING DIAGRAMS article.
  3. With A/C mode selector in the ON position, battery voltage should be present. If battery voltage is not present, check for open between A/C mode select switch and PCM A/C request terminal, low A/C refrigerant level causing low pressure switch to open, bad A/C fuse or bad A/C mode select switch.

Fuel Injector Balance Test

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. An injector with a pressure drop of 1.5 psi (.11 kg/cm 2 ) or more, greater than or less than other injectors, should be considered faulty.

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

CAUTIONTo avoid possible vehicle fire, wrap a shop towel around fitting to absorb fuel spillage.
  1. Ensure engine is at normal operating temperature. Connect Fuel Pressure Gauge (J-34730-1) to pressure test port. Energize fuel pump using fuel pump test connector or Tech 1 scan tool.
  2. Bleed air from fuel gauge and hose to ensure accurate gauge reading. Repeat this procedure until all air is bled from system. Run fuel pump and note fuel pressure. Fuel pressure should be as specified. See «FUEL PRESSURE RANGE CHART»(ref-20510-S09605570752001010200000) . If fuel pressure range is not as specified, see BASIC FUEL SYSTEM CHECKS in the «BASIC TESTING - 3.8L»(ref-20653) article.
  3. Turn fuel pump off. When fuel pump stops, pressure may slightly drop then should hold steady. If fuel pressure does not hold steady, refer to BASIC FUEL SYSTEM CHECKS in the «BASIC TESTING - 3.8L»(ref-20653) article.
  4. Install Fuel Injector Tester (J-39021) to an injector. Set amperage supply selector switch to BALANCE TEST, 0.5-2.5 AMP position. Cycle fuel pump on and off to pressurize fuel system. Record stabilized fuel pressure.
  5. Depress PUSH TO START TEST button on fuel injector tester to energize injector. Note fuel pressure the instant fuel gauge needle stops. Record fuel pressure reading. Perform the same test to all injectors.
  6. To obtain pressure drop values, subtract second pressure reading from first pressure reading on each injector. Add all pressure drop values and divide by number of injectors to obtain an average pressure drop.
  7. Retest an injector that appears faulty. Replace any injector with a 1.5 psi (.11 kg/cm 2 ) difference, either greater than or less than the average pressure drop. If injectors are all okay, remove test equipment, plug in disconnected harness connectors and review SYMPTOMS in the «TESTS W/O CODES - 3.8L»(ref-20706) article.
ApplicationPsi (kg/cm 2 )
3.8L48-55 (3.4-3.9)

FUEL PRESSURE RANGE CHART

Injector Leak Test

  1. Turn engine off. Relieve fuel pressure. Access fuel injector harness connector. Connect Fuel Injector Tester (J-39021) to vehicle battery and to a fuel injector. If coolant temperature is 50-95°F (10-35°C), go to next step. If coolant temperature is not 50-95°F (10-35°C), go to step 5).
  2. Set fuel injector tester's amperage supply selector switch to COIL TEST 0.5 AMP position. Connect a Digital Volt-Ohmmeter (DVOM) to fuel injector tester. Set DVOM to tenths scale (0.0).
  3. Ensure engine coolant temperature is 50-95°F (10-35°C). Press PUSH TO START TEST button. Observe DVOM. Voltage reading may climb during test. Record lowest voltage displayed immediately after activation.
  4. Perform voltage reading on all injectors. If voltage reading is erratic or falls out of specified range, perform injector balance test or replace faulty injector. See «INJECTOR TEST VOLTAGE RANGE»(ref-20510-S23449628292001010200000) table or FUEL INJECTOR BALANCE TEST.
  5. Press PUSH TO START button on fuel injector tester. Observe DVOM. Voltage reading may climb during test. Record lowest voltage displayed immediately after activation. Perform voltage reading at least twice on all injectors.
  6. If voltage reading is erratic or is greater than 9.5 volts, replace affected fuel injector. If voltage reading is not erratic or not greater than 9.5 volts, go to next step.
  7. From recorded voltages (except readings greater than 9.5 volts), identify highest voltage reading and subtract from the other recorded voltages. If subtracted value is greater than 0.6 volts, replace affected fuel injector. If subtracted value is less than 0.6 volts, perform injector balance test. See FUEL INJECTOR BALANCE TEST.
ApplicationVolts
3.8L5.7-6.6

INJECTOR TEST VOLTAGE RANGE

System Test (Vacuum Operated)

Start and run engine to normal operating temperature. With engine at idle, push up on underside of EGR diaphragm. RPM should drop as EGR valve is opened. If RPM does not drop, remove EGR valve and check for blocked EGR passages. If RPM drops as diaphragm is lifted and EGR vacuum supply is regulated by an PCM-controlled solenoid, verify vacuum is available to solenoid at 2000 RPM and check solenoid using appropriate procedure. See appropriate EGR CONTROL SOLENOID procedure.

CAUTIONWear gloves if handling EGR valve when it is hot.

Warning Light Diagnosis

  1. Perform On-Board Diagnostics (OBD) System check. See the «BASIC TESTING - 3.8L»(ref-20653) 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 appropriate diagram in 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 panel cluster, but leave 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 panel 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 panel 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 panel 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 panel cluster and at PCM. If problem is present, repair as necessary and then go to step 17). If problem was not present, 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 OUTPUT TESTS 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 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 panel 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).

Compressor Clutch Control Circuit Diagnosis

  1. If On-Board Diagnostic (OBD) System Check has not been performed, see the «BASIC TESTING - 3.8L»(ref-20653) 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 - 3.8L»(ref-20509) 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 the 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. 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 the 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).

Cooling Fan Circuit Diagnosis

  1. If On-Board Diagnostic (OBD) System Check has not been performed, see the «BASIC TESTING - 3.8L»(ref-20653) article and go to OBD SYSTEM CHECK. If OBD SYSTEM CHECK has been performed, go to next step.
  2. Check if any Diagnostic Trouble Codes (DTCs) are present. If DTCs are present, perform testing for applicable DTC. See the «TESTS W/CODES - 3.8L»(ref-20509) 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. Start engine and let idle. If fans are off, go to next step. If fans are not off, go to step 32).
  4. Using scan tool, select RELAY CONTROL function. Command low speed fans 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. Command high speed fans on. If both fans run at high speed, go to next step. If both fans do not run at high speed, go to step 58).
  6. Ensure ambient temperature is greater than 48°F (9°C). Exit scan tool OUTPUT TESTS. Start engine and let idle. Turn A/C on. If fans come on, go to DIAGNOSTIC AIDS. If fans do not come on, go to next step.
  7. Using scan tool, view A/C REQUEST on display. If scan tool displays YES, go to step 77). If scan tool does not display YES, go to appropriate A/C CLUTCH CIRCUIT DIAGNOSIS TEST in «A/C COMPRESSOR CLUTCH CONTROLS»(ref-20510-S35262600922001010200000) .
  8. If either cooling fan is running, go to next step. If neither cooling fan is running, go to step 16).
  9. If left-side cooling fan is running, go to next step. If left-side cooling fan is not running, go to step 14).
  10. Turn ignition off. Disconnect right-side cooling fan motor harness connector. Turn ignition on. Using scan tool, select RELAY CONTROL function. Command low speed fans on. If left-side cooling fan runs, go to next step. If left-side cooling fan does not run, go to step 80).
  11. Remove No. 3 cooling fan relay from underhood electrical center. If left-side cooling fan runs, go to next step. If left-side cooling fan does not run, go to step 13).
  12. Locate and repair short to ground in circuit No. 532 (Gray wire) between left-side cooling fan motor and No. 3 cooling fan relay. Go to step 81).
  13. Check for short to ground in circuit No. 504 (White wire) between No. 2 cooling fan relay and No. 3 cooling fan relay, or between No. 2 cooling fan relay and right-side cooling fan motor. Repair as necessary. Go to step 81). If no problem was found, go to step 76).
  14. Turn ignition off. Disconnect left-side cooling fan motor harness connector. Turn ignition on. Using scan tool, select RELAY CONTROL function. Command low speed fans on. Is right-side cooling fan runs, go to next step. If right-side cooling fan does not run, go to step 79).
  15. Replace left-side cooling fan motor 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 D1. If test light comes on, go to step 18). If test light does not come on, go to next step.
  17. Check for blown fusible link that supplies power to No. 1 cooling fan relay. If fusible link 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 circuits No. 402, 409 and 504. If fuse is not blown, check for an open in circuit No. 402 between fusible link 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 D5. If test light comes on, go to step 20). If test light does not come on, go to next step.
  19. Check for blown A/P FAN fuse (25-amp) that supplies power to No. 1 cooling fan relay. If fuse is blown, locate and repair short circuit. Possible causes for short circuit are: Short to ground in circuit No. 1440. Shorted relay coil in cooling fan relay(s). If fuse is not blown, check for an open in circuit No. 1440. Repair as necessary. Go to step 81).
  20. Turn ignition off. Disconnect both cooling fan harness connectors. Using fused jumper wires, connect terminals "A" and "B" together at both harness connectors. Turn ignition on. Connect a test light between No. 1 cooling fan relay cavities D1 and D4. 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 D2 and D5. 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 D1 and D4. 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 D2 and D5. Turn ignition on. Using a test light connected to ground, probe PCM harness connector C1, terminal No. 32. 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 Dark Green wire between No. 1 cooling fan relay and PCM harness connector C1, terminals No. 11 or 32. After repair, 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 D1 and D4. Remove No. 3 cooling fan relay from underhood electrical center. Using a test light connected to ground, probe No. 3 cooling fan relay cavity J4. 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 No. 3 cooling fan relay cavities J3 and J4. 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. 504 (White wire) between No. 3 cooling fan relay cavity J3 and harness connector terminal "B" at right-side cooling fan motor. Repair as necessary. Go to step 81). If no problem was found, go to step 57).
  30. Check for poor connections at No. 3 cooling fan relay cavities J3 or J4 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. 409 (Light Blue wire) between No. 1 cooling fan relay cavity D4 and harness connector terminal "B" at left-side cooling fan motor. 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-20510-S35262600922001010200000) . 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. 409 (Light Blue wire). Go to step 81).
  36. Using a test light connected to battery positive, probe No. 1 cooling fan relay cavity D2. 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 D2. 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 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 scan tool reading is 1.2 volts or greater, go to step 44).
  42. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on. If right-side cooling fan operates at high speed, go to next step. If right-side cooling fan does not operate at high speed, go to step 77).
  43. Check for a short to ground in No. 2 and 3 cooling fan relay 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 right-side cooling fan operates at high speed, go to next step. If right-side cooling fan does not operate at high speed, go to step 70).
  53. Remove No. 3 cooling fan relay from underhood electrical center. If right-side cooling fan operates at high speed, go to next step. If right-side cooling fan does not operate at high speed, go to step 55).
  54. Locate and repair short to power in circuit No. 504 (White wire) between No. 2 cooling fan relay and right-side cooling fan motor. Go to step 81).
  55. Locate and repair short to power in circuit No. 532 (Gray wire) between No. 3 cooling fan relay and left-side cooling fan motor. Go to step 81).
  56. Check for an open in circuit No. 532 (Gray wire) between No. 3 cooling fan relay cavity J4 and terminal "A" of left-side cooling fan motor 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. 150 (Black wire) between right-side cooling fan motor 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 F2 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 No. 3 cooling fan relay from underhood electrical center. Connect a test light between No. 3 cooling fan relay cavity J2 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. Turn ignition on. Check No. 2 and 3 cooling fan relay control circuit (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 right-side cooling fan motor 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 left-side cooling fan motor 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 windings. 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 F5. If test light does not come on, go to next step. If test light comes on, go to step 66).
  65. Locate and repair open in battery positive circuit to No. 2 cooling fan relay. Check for blown A/P FAN fuse (25-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 F4. 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 F4. Go to step 81).
  68. Check for open in circuit No. 504 (White wire) between right-side cooling fan motor harness connector terminal "B" and No. 2 cooling fan relay cavity F1. 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 No. 3 cooling fan relay from underhood electrical center. Turn ignition on. Using a test light connected to ground, probe No. 3 cooling fan relay cavity J5. If test light does not come on, go to next step. If test light comes on, go to step 73).
  72. Locate and repair open in battery positive circuit to No. 3 cooling fan relay cavity J5. Go to step 81).
  73. Using a test light connected to battery positive, probe No. 3 cooling fan relay cavity J1. 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 between No. 3 cooling fan relay cavity J1 and ground. Go to step 81).
  75. Check for poor connections at No. 3 cooling fan relay in underhood electrical center. Repair as necessary. Go to step 81). If no problem was found, go to step 76).
  76. Replace No. 3 cooling fan relay. Go to step 81).
  77. Replace PCM. Go to step 81).
  78. Repair open in Dark Blue wire between PCM harness connector C1, terminal No. 31 and No. 2 cooling fan relay cavity F2. Go to step 81).
  79. Replace left-side cooling fan motor. Go to step 81).
  80. Replace right-side cooling fan motor. 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 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.

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