Engine Controls - System/component Tests - 2.3L: Diagnosis

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»(ref-19614-S23375575822001110200000).
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.

CAUTION

To avoid possible vehicle fire, wrap a shop towel around fitting to absorb fuel spillage.

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.
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. If fuel pressure range is not as specified, see BASIC FUEL SYSTEM CHECKS in «BASIC TESTING»(ref-19653) article in this section.
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.
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.
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.
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.
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.

Application	Psi (kg/cm 2 )
2.3L	41-47 (2.9-3.3)

FUEL PRESSURE RANGE CHART

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

Cooling fan is controlled by Powertrain Control Module (PCM) based on inputs from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, A/C control switch, A/C refrigerant pressure sensor and Vehicle Speed Sensor (VSS). PCM grounds circuit No. 335, energizing cooling fan relay and turning on cooling fan. Cooling fan is turned on when engine coolant temperature is greater than 217°F (103°C), A/C clutch is requested or vehicle speed is less than 35 MPH. If Diagnostic Trouble Code (DTC) 14 or 15 is set, engine coolant temperature is greater than 239°F (115°C) or A/C refrigerant pressure is high, fan relay is energized regardless of vehicle speed.

Under certain high temperature conditions, cooling fan will continue to run for up to 7 minutes after ignition is off. Fan run-on occurs when ECT sensor indicates greater than 212°F (100°C) and IAT sensor indicates greater than 176°F (80°C); ECT sensor indicates greater than 234°F (112°C) and IAT sensor indicates greater than 158°F (70°C); or ECT sensor indicates greater than 241°F (116°C).

Note. Test numbers refer to numbers on diagnostic chart.

With fan relay activated, cooling fan driver should close, energizing cooling fan relay.
Tests if fault is in wiring or fan relay connection.

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 (2.3L) Cooling Fan Circuit Diagnosis. Scheme 104

Scheme 104: Chart C-12 Schematic (2.3L) Cooling Fan Circuit Diagnosis

Chart C-12 Flow Chart (2.3L) Cooling Fan Circuit Diagnosis. Scheme 105

Scheme 105: Chart C-12 Flow Chart (2.3L) Cooling Fan Circuit Diagnosis

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: hot engine restart, Wide Open Throttle (WOT), engine RPM greater than 6000 RPM and IAC reset. A/C compressor clutch will remain disengaged if Diagnostic Trouble Code (DTC) 66 is present, refrigerant pressure is too low or high, and no A/C request signal exists from A/C select switch or circuit.

Note. Test numbers refer to numbers on diagnostic chart.

If DTCs are present, diagnose DTCs first. Refer to the «TESTS W/CODES - 2.3L»(ref-19584) article in this section. PCM will energize A/C compressor clutch relay only when engine is running. This test determines whether relay or circuit No. 459 is faulty.
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.

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 43-428 psi (3.0-30.1 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 (2.3L) A/C Compressor Clutch Circuit Diagnosis. Scheme 106

Scheme 106: Chart C-10 Schematic (2.3L) A/C Compressor Clutch Circuit Diagnosis

Chart C-10 Flow Chart (2.3L - 1 Of 2) A/C Compressor Control Circuit Diagnosis. Scheme 107

Scheme 107: Chart C-10 Flow Chart (2.3L - 1 Of 2) A/C Compressor Control Circuit Diagnosis

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

Note. Test numbers refer to numbers on diagnostic chart.

Determines if A/C pressure sensor is out-of-range, causing A/C compressor clutch to be disengaged.
With engine off and field service mode activated, PCM should ground circuit No. 459, causing test light to come on.

PCM will disable A/C compressor if refrigerant pressure is not 43-428 psi (3.0-30.1 kg/cm 2 ). If refrigerant is okay, check A/C pressure sensor circuit. If A/C pressure sensor circuit is okay, replace pressure sensor.