Engine Controls - System/component Tests - 3.1L: Diagnosis Oldsmobile Achieva I

A/C ON (A/C Request) Switch Test

1. 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.
2. 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»(ref-19615-S23713567922001110200000).
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 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.

MFI 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 MFI INJECTOR BALANCE TEST should not be repeated more than once without starting and running engine.

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 tester.
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»(ref-19615-S37009655932001110200000) chart. If fuel pressure range is not as specified, see BASIC FUEL SYSTEM CHECKS in «BASIC TESTING»(ref-19653) article in this section.
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 «BASIC TESTING»(ref-19653) article in this section.
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 «TESTS W/O CODES»(ref-19654) article in this section.

FUEL PRESSURE RANGE CHART

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.

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.

CHART C-12, COOLING FAN CIRCUIT DIAGNOSIS (1 OF 2)

Battery voltage is supplied to cooling fan relay by circuit No. 2 at cooling fan relay terminals No. 30 and 85. When Powertrain Control Module (PCM) grounds circuit No. 335, relay is energized and cooling fan is turned on. When engine is running, PCM will energize cooling fan if Diagnostic Trouble Code (DTC) 14, 15 or 70 is set, vehicle speed is less than 70 MPH, engine coolant temperature is greater than 226°F (108°C), A/C refrigerant pressure is greater than 187 psi (13.1 kg/cm 2 ), or PCM is in back-up mode.

Note. Test numbers refer to numbers on diagnostic charts.

1. With diagnostic terminal grounded, cooling fan control driver will close, energizing fan control relay.
2. If A/C pressure is greater than 300 psi (21.1 kg/cm 2 ) or circuit is open, fan runs whenever A/C is requested.
3. With A/C compressor clutch engaged and A/C pressure sensor functioning properly, fan should come on when pressure exceeds about 200 psi (14.1 kg/cm 2 ). This signal should cause PCM to energize cooling fan relay. If referred to a C-10 chart, see appropriate C-10 chart.
4. This will determine whether A/C pressure sensor, PCM or circuitry is faulty.

Diagnostic Aids

If an overheating condition is suspected, check if it is caused by 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 Engine Coolant Temperature (ECT) sensor temperature using a scan tester. ECT sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.

Chart C-12 Schematic (3.1L V6) Cooling Fan Circuit Diagnosis. Scheme 121

Chart C-12 Flow Chart (3.1L V6 - 1 Of 2) Cooling Fan Circuit Diagnosis. Scheme 122

CHART C-12, COOLING FAN CIRCUIT DIAGNOSIS (2 OF 2)

Note. Test numbers refer to numbers on diagnostic charts.

1. Battery voltage should be available at cooling fan relay terminals No. 30 and 85.
2. Checks ability of PCM to ground circuit No. 335.
3. If fan does not turn on at this point, circuit No. 409 is open or cooling fan motor is faulty.

Chart C-12 Flow Chart (3.1L V6 - 2 Of 2) Cooling Fan Circuit Diagnosis. Scheme 123

CHART C-10, A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS (1 OF 2)

A/C compressor clutch relay is controlled by the Powertrain Control Module (PCM). The PCM provides a ground on circuit No. 459 and A/C is requested. PCM will delay A/C compressor clutch engagement momentarily after A/C is requested. This delay allows Idle Air Control (IAC) valve to adjust engine RPM for additional load.

PCM will temporarily disengage A/C compressor clutch for a precalibrated time during one or more of the following conditions: engine not running, engine coolant temperature greater than 255°F (124°C), A/C refrigerant pressure less than 38 psi (2.7 kg/cm 2 ) or greater than 429 psi (30.2 kg/cm 2 ), or if Diagnostic Trouble Code (DTC) 66 or 70 is present and no A/C request signal exists from A/C select switch or circuit.

Note. Test numbers refer to numbers on diagnostic chart.

1. If DTCs are present, diagnose DTCs first. PCM will energize A/C relay only when engine is running. Determines whether relay or circuit No. 459 is faulty.
2. Determines if signal is reaching PCM through circuit No. 66 from A/C control panel. Signal should only be present when A/C mode or defrost mode is selected.

Check branch circuits and splices to other components. If complaint is insufficient cooling, problem may be caused by an inoperative cooling fan. See CHART C-12 for cooling fan diagnosis. If cooling fan operates correctly, problem is a basic A/C system problem. PCM will disable A/C compressor if refrigerant pressure is not 38-429 psi (2.7-30.2 kg/cm 2 ). If refrigerant pressure is okay, check A/C pressure sensor circuit. If A/C pressure sensor circuit is okay, replace A/C pressure sensor.

Chart C-10 Schematic (3.1L V6) A/C Compressor Clutch Circuit Diagnosis. Scheme 124

Chart C-10 Flow Chart (3.1L V6 - 1 Of 2) A/C Compressor Clutch Circuit Diagnosis. Scheme 125

CHART C-10, A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS (2 OF 2)

Note. Test number refers to number on diagnostic chart.

1. Determines if A/C refrigerant pressure sensor is out-of-range, causing A/C compressor to be disengaged.
2. With engine off and A/C relay output test activated, PCM should be grounding circuit No. 459, causing test light to come on.

Check branch circuits and splices to other components. If complaint is insufficient cooling, problem may be caused by an inoperative cooling fan. See CHART C-12 for cooling fan diagnosis. If cooling fan operates correctly, problem is a basic A/C system problem.

PCM will disable A/C compressor if refrigerant pressure is not 38-429 psi (2.7-30.2 kg/cm 2 ). If refrigerant pressure is okay, check A/C pressure sensor circuit. If A/C pressure sensor circuit is okay, replace A/C pressure sensor.

Chart C-10 Flow Chart (3.1L V6 - 2 Of 2) A/C Compressor Clutch Circuit Diagnosis. Scheme 126

Scheme 127

3.1L (VIN M) PCM Wiring Diagram (1 Of 2). Scheme 128

3.1L (VIN M) PCM Wiring Diagram (2 Of 2). Scheme 129

See also:
• SENSOR RANGE CHARTS
• ADJUSTMENTS