A/C ON (A/C REQUEST) SWITCH TEST
- Start engine and allow to idle. If a scan tester is available, scan A/C request parameter. Move A/C mode selector back and forth between ON and OFF positions. Scan status should change.
- If scan tester is not available or scan status does not change, measure voltage between ground and ECM A/C request terminal. For wiring schematics, see mini-schematics under A/C CLUTCH (C-10) & ELECTRIC COOLING FAN (C-12) under MISCELLANEOUS CONTROLS.
- With A/C mode selector in the ON position, 12 volts should be present. If 12 volts are not present, check for open between A/C mode select switch and ECM 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.
PFI Injector Balance Test (C-2)
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 PFI INJECTOR BALANCE TEST should not be repeated more than once without starting and running engine.
| CAUTION | To avoid possible vehicle fire, wrap a shop towel around fitting to avoid fuel spillage. |
- With ignition off, connect Fuel Pressure Gauge (J-34730-1) to pressure tap. Unplug harness connector at all injectors. Connect Injector Tester (J-34730-3) to one of the injectors.
- Follow manufacturer's instructions when installing adapter harness. Ignition should be turned off at least 10 seconds to complete ECM shutdown cycle.
- 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.
- Turn ignition on again to bring fuel pressure to maximum. Record initial pressure reading. Energize tester one time and note pressure drop at lowest point.
- Disregard any slight pressure drop after low point is reached. Subtracting second pressure reading from initial reading indicates amount of injector pressure drop.
- 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 TESTS W/O CODES article in this section.
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 ECM-controlled solenoid, verify vacuum is available to solenoid at 2000 RPM and check solenoid using appropriate procedure. See appropriate EGR CONTROL SOLENOID procedure below.
| CAUTION | Wear gloves if handling EGR valve when it is hot. |
DIAGNOSTIC CHARTS
Note. In the following diagnostic tests, schematics, illustrations and flow charts are courtesy of General Motors Corp.
Note. In following charts, the terms ECM and PCM can be used interchangeably.
Diagnostic Aids
If an overheating condition is suspected, verify if it is due to an actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.
If vehicle is overheating and gauge or light indicates so but cooling fan is not coming on, check coolant sensor temperature using a Tech 1 scan tester. Sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
Scheme 42
Scheme 43
If complaint was insufficient cooling, problem may be caused by an inoperative cooling fan or A/C low pressure switch. Engine cooling fan should turn on when A/C pressure exceeds a value to close low pressure switch, which causes ECM to energize cooling fan relay. See CHART C-12 for cooling fan diagnosis. If fan operates correctly, check for basic A/C system problem.
Scheme 44
If an overheating condition is suspected, verify if it is due to an actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.
If vehicle is overheating and gauge or light indicates so but cooling fan is not coming on, check coolant sensor temperature using a scan tester. Sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
Scheme 45
Scheme 46
If complaint was insufficient cooling, problem may be caused by an inoperative cooling fan or A/C low pressure switch. Engine cooling fan should turn on when A/C pressure exceeds a value to close low pressure switch, which causes ECM to energize cooling fan relay. See CHART C-12 for cooling fan diagnosis. If fan operates correctly, check for basic A/C system problem.
Scheme 47
If an overheating condition is suspected, verify if it is due to an actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.
If vehicle is overheating and gauge or light indicates so but cooling fan is not coming on, check coolant sensor temperature using a Tech 1 scan tester. Sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
Scheme 48
Scheme 49
If complaint was insufficient cooling, problem may be caused by an inoperative cooling fan. See CHART C-12 for cooling fan diagnosis. If fan operates correctly, check for basic A/C system problem. If A/C pressure is out of range (43-428 psi), ECM will disable compressor. Using Tech 1 scan tester, observe A/C pressure for 2 minutes with engine at idle and A/C on. Pressure should be within 20 psi of actual reading. If pressure goes out of range, check for basic A/C system problem. If pressure was okay, check circuit using Code 66 chart or replace A/C pressure sensor.
Scheme 50
Scheme 51
If complaint was insufficient cooling, problem may be caused by an inoperative cooling fan or A/C low pressure switch. Engine cooling fan should turn on when A/C pressure exceeds a value to close low pressure switch, which causes ECM to energize cooling fan relay. See CHART C-12 for cooling fan diagnosis. If fan operates correctly, check for basic A/C system problem.
Scheme 52
If cooling fan operates normally but an overheating condition exists, check coolant temperature sensor temperature-to-resistance value. See Code 15 chart in appropriate TESTS W/CODES article in this section. Replace coolant temperature sensor if not within specifications. If coolant temperature sensor is okay, check for basic cooling system problem.
Scheme 53
Scheme 54
If cooling fan operates normally but an overheating condition exists, check coolant temperature sensor temperature-to-resistance value. See CODE 14 chart in appropriate TESTS W/CODES article in this section. Replace coolant temperature sensor if mis-scaled or out of calibration. If coolant temperature sensor is okay, check for basic cooling system problem.
Scheme 55
Incorrect fan operation or overheating may be caused by a mis-scaled coolant temperature sensor or faulty A/C pressure sensor. Check coolant sensor temperature using a Tech 1 scan tester. Sensor may have shifted out of calibration and should be replaced. See TEMPERATURE-TO-RESISTANCE VALUES table on Code 14 chart in appropriate TESTS W/CODES article in this section. Compare A/C pressure on Tech 1 scan tester with actual system pressure using a gauge. Replace A/C pressure sensor if faulty.
Scheme 56
Scheme 57
If an overheating condition is suspected, verify if it is due to actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.
If vehicle is overheating and gauge or light indicates so but cooling fan is not coming on, check coolant sensor temperature using a scan tester. Sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
Scheme 58
If an overheating condition is suspected, verify if condition is due to an actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.
If vehicle is overheating and gauge or light indicates so but cooling fan is not coming on, check coolant sensor temperature using a scan tester. Sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
Scheme 59
If complaint is insufficient cooling, problem may be caused by an inoperative cooling fan. See CHART C-12 for cooling fan diagnosis. If fan operates correctly, check for basic A/C system problem.
Scheme 60
Scheme 61
Scheme 62
If an overheating condition is suspected, verify if condition is due to an actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.
If vehicle is overheating and gauge or light indicates so but cooling fan is not coming on, check coolant sensor temperature using a Tech 1 scan tester. Sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
Scheme 63
Scheme 64
Before proceeding with CHART C-10, ensure that no diagnostic trouble code(s) are present. ECM will not energize A/C clutch with a stored diagnostic trouble code.
Scheme 65
Scheme 66
Scheme 67
If an overheating condition is suspected, verify if it is due to an actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.
If vehicle is overheating and gauge or light indicates so but cooling fan is not coming on, check coolant sensor temperature using a Tech 1 scan tester. Sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
Scheme 68
Scheme 69
If complaint is insufficient cooling, problem may be an inoperative cooling fan. See CHART C-12 for cooling fan diagnosis. If fan operates normally, ensure A/C system is functioning properly. If A/C pressure is not 41-428 psi (2.9-30.1 kg/cm 2 ), ECM will disable compressor. Using Tech 1 scan tester, observe A/C pressure for 2 minutes with engine idling and A/C on. If pressure is out of range, adjust A/C refrigerant charge. Tech 1 scan tester pressure reading should be within 20 psi (1.4 kg/cm 2 ) of actual pressure. If Tech 1 scan tester pressure reading is not within 20 psi (1.4 kg/cm 2 ), refer to Code 66 chart in appropriate TESTS W/CODES article in this section or replace A/C pressure sensor.
Scheme 70
Scheme 71
If complaint is insufficient cooling, problem may be an inoperative cooling fan. See CHART C-12 for cooling fan diagnosis. If A/C pressure is not 41-428 psi (2.9-30.1 kg/cm 2 ), ECM will disable compressor. Using Tech 1 scan tester, observe A/C pressure for 2 minutes with engine idling and A/C on. If pressure is out of range, adjust A/C refrigerant charge.
Scheme 72
An intermittent can be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation. Check for backed out PCM terminals GC4 or GC3, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and a damaged harness. If connections and harness are okay, connect a DVOM between affected terminal and ground. Move related wiring and connectors. If a failure is induced, voltage reading will change. Check for a mis-scaled coolant temperature sensor. See CODE 15 chart in appropriate TESTS W/CODES article in this section. Also check for a basic cooling system problem.
Scheme 73
Scheme 74
CHART C-12A - COOLING FAN CIRCUIT DIAGNOSIS (1 OF 5)(3.8L "E" BODY)
PCM uses 3 relays to control 2 cooling fans. Both fans run at low speed when PCM energizes cooling fan relay "G" through PCM terminal GC4 when coolant temperature exceeds 214°F (101°C) or when A/C high side refrigerant temperature exceeds 122°F (50°C). Both fans run at high speed when PCM energizes all 3 relays with coolant temperature exceeding 226°F (108°C) or when A/C high side refrigerant temperature exceeds 149°F (65°C).
Note. Test numbers refer to test numbers on diagnostic charts.
- Codes 14 or 15 could mean coolant system or coolant temperature sensor operation is not normal, so fan(s) operation cannot be checked correctly.
- Selecting output tests, Fan 1 with Tech 1 scan tester grounds fan relay "G" through PCM. Fans should cycle on and run at low speed.
- Selecting output tests, Fan 2 should cause PCM to energize fan relays "G", "C", and "D". Both fans should run at high speed.
An intermittent can be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation. Check for backed out PCM terminals GC4 or GC3, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and a damaged harness. If connections and harness are okay, connect a DVOM between affected terminal and ground. Move related wiring and connectors. If a failure is induced, voltage reading will change. Check for a mis-scaled coolant temperature sensor. See Code 15 chart in appropriate TESTS W/CODES article in this section. Also check for a basic cooling system problem.
Scheme 75
Scheme 76
Cooling fans should be off if coolant temperature is less than 208°F (98°C) and high side temperature is less than 122°F (50°C). On-board diagnostics may assist in diagnosing cooling fan problem. Monitor parameters ED04 and BD21 for coolant temperature and parameter BD27 for A/C high side temperature sensor. See appropriate TESTS W/CODES article in this section for instructions on using on-board diagnostics. Disconnecting A/C high side temperature sensor should result in BD27 reading of less than -30°F (-35°C). If BD27 reading is not -30°F (-35°C), see Code B111 chart in appropriate TESTS W/CODES article in this section.
Disconnecting coolant temperature sensor should cause BD21 to read less than -30°F (-35°C). If BD21 reading is not less than -30°F (-35°C), see CODE 14 or CODE 15 chart in appropriate TESTS W/CODES article in this section. BD27 should read about 122°F (50°C) when A/C high side pressure is about 160 psi (11.2 kg/cm 2 ). Comparing these might isolate a bad sensor.
Normal cooling fan operation requires low speed if engine is running, vehicle speed is less than 45 MPH and coolant temperature exceeds 214°F (101°C) or A/C high side temperature is greater than 122°F (50°C).
Scheme 77
If cooling fans operate normally but an overheat condition exists, see COOLANT TEMPERATURE-TO-RESISTANCE VALUES table in CODE 15 chart in appropriate TESTS W/CODES article in this section. Replace coolant temperature sensor if mis-scaled. If coolant temperature sensor is okay, check for basic cooling system problem.
If coolant temperature exceeds 230°F (110°C) and manifold air temperature exceeds 102°F (39°C) with ignition off, ECM will energize cooling fans at low speed for up to 2 minutes or until coolant temperature is less than 210°F (99°C).
Scheme 78
Scheme 79
If cooling fans operate normally but overheat condition exists, see COOLANT TEMPERATURE-TO-RESISTANCE VALUES table in CODE 14 chart in appropriate TESTS W/CODES article in this section. Replace coolant temperature sensor if mis-scaled. If coolant temperature sensor is okay, check for basic cooling system problem.
Scheme 80
If cooling fans operate normally but overheat condition exists, see COOLANT TEMPERATURE-TO-RESISTANCE VALUES table in CODE 14 chart in appropriate TESTS W/CODES article in this section. Replace coolant temperature sensor if mis-scaled. If coolant temperature sensor is okay, check for basic cooling system problem.
