Engine Control System - System/component Tests Pontiac Trans Sport II

INTRODUCTION

Before testing separate components or systems, perform procedures in the BASIC TESTING article. Since many computer-controlled and monitored components set a trouble code if they malfunction, also perform procedures in the TESTS W/CODES article.

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter and refer to the WIRING DIAGRAMS article to isolate wiring harness shorts or opens.

The following table provides the location of commonly used diagnostic information.

GENERAL MOTORS REFERENCE

CONTROL UNIT

Note. To perform the following ground and power tests, use appropriate wiring diagram in the WIRING DIAGRAMS article.

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on PCM/VCM ground terminals. Resistance should be zero ohms. If not, repair open to ground.
2. Using a voltmeter, touch negative lead of voltmeter to a good ground. Touch positive lead of voltmeter to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If voltmeter reading is more than one volt, check for open, corrosion or loose connection on ground circuit.

Power Circuits

1. Using a voltmeter, check for battery voltage between PCM/VCM continuous power terminal(s) and ground. If battery voltage is not present, check for blown fuse or open fusible link. If okay, check for open in wire between PCM/VCM terminal and power source.
2. Turn ignition on. Using a voltmeter, check for battery voltage between PCM/VCM ignition power terminals and ground. If battery voltage is not present, check IGN fuse. If fuse is okay, check for an open in wire between battery and ignition switch, and between ignition switch and PCM/VCM terminal. If okay, check for a defective ignition switch.
3. Connect voltmeter between ground and PCM/VCM starter (crank) signal terminal. On vehicles with manual transmission/transaxle, depress clutch pedal. Turn ignition switch to START position. Battery voltage should be present ONLY when ignition switch is in START position.
4. If voltage is not present, check CRANK fuse or fusible link between ignition switch and PCM/VCM terminal. If fuse or fusible link is okay, check for an open in wire between ignition switch and PCM/VCM terminal, or check for a defective ignition switch.

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.

BRAKE SWITCH

Disconnect brake switch harness connector. Using an ohmmeter, check continuity between brake switch terminals. Continuity should be present. Depress brake pedal or activate brake switch, continuity should not be present.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

If a coolant sensor-related code is present, see the TESTS W/CODES article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test sensor calibration. Disconnect ECT sensor connector. Measure resistance between sensor terminals. Resistance should be high when engine is cold and drop as engine warms. See ECT SENSOR RESISTANCE VALUES table.

ECT SENSOR RESISTANCE VALUES

Note. Intake Air Temperature (IAT) sensor is also referred to as Manifold Air Temperature (MAT) sensor.

INTAKE AIR TEMPERATURE (IAT) SENSOR

If an IAT sensor-related code is present, see the TESTS W/CODES article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test calibration. Disconnect IAT sensor harness connector. Connect ohmmeter between sensor terminals. Sensor resistance should be as specified. See IAT SENSOR RESISTANCE table. With vehicle sitting overnight, IAT sensor and coolant sensor should have close to the same resistance reading.

IAT SENSOR RESISTANCE

KNOCK SENSOR

1. Disconnect knock sensor harness connector. Using an ohmmeter, measure knock sensor resistance between sensor terminal and engine block. Resistance should be 3300-4500 ohms. Connect voltmeter between sensor terminal and ground. Set voltmeter to 2-volt AC scale.
2. Start and idle engine. Tap on engine block near sensor. A signal should be indicated on voltmeter. If no signal is indicated, replace knock sensor. Also see «TIMING CONTROL SYSTEMS»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests) under IGNITION SYSTEM and the «TESTS W/CODES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wcodes) article.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

1. MAP sensor circuit malfunction should set a related code in PCM/VCM memory. If a code is present, see the «TESTS W/CODES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wcodes) article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test sensor calibration. If driveability problems exist, MAP sensor failure is suspected and no MAP code is present, disconnect MAP sensor connector. If driveability condition improves, check MAP vacuum hose for splits, kinks, proper routing and blockage. If no problems are found, replace MAP sensor.
2. With ignition on and engine off, check MAP sensor parameter using a scan tool connected to Data Link Connector (DLC). Voltage should be as specified in «MAP SENSOR VOLTAGE RANGE»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests) table.
3. If MAP sensor voltage is as specified, go to next step. If voltage is not as specified, check 5-volt reference supply to sensor. Check harness integrity. If no problems are evident, replace MAP sensor.
4. Using a hand-held vacuum pump, apply 10 in. Hg to MAP sensor and note voltage change. Voltage should drop to about 1.0-2.5 volts less than specified in table. If voltage is not as specified or voltage reading does not immediately follow vacuum change, MAP sensor is faulty.

MAP SENSOR VOLTAGE RANGE

OXYGEN SENSOR (O2S)

1. Start engine and warm to operating temperature. Disconnect oxygen sensor. Connect DVOM between Purple wire of oxygen sensor and ground. Place DVOM on 2-volt scale.
2. Using another DVOM on 20-volt scale, connect DVOM in series between Purple wire from PCM/VCM and positive post of battery. This will simulate a rich condition, causing PCM/VCM to respond by leaning mixture. Reading on DVOM connected to oxygen sensor should decrease to less than .3 volt.
3. Move DVOM lead from positive battery post to negative battery post. This will simulate a lean condition, causing PCM/VCM to respond by richening mixture. Reading on DVOM connected to oxygen sensor should increase to greater than .8 volt. If reading does not change as specified, replace oxygen sensor.
4. If a second DVOM is not available, connect a jumper in Purple wire from PCM/VCM. Hold jumper in one hand and touch positive post of battery with other hand to simulate a rich condition. Touch negative post of battery to simulate a lean condition. For additional testing procedures, see the «TESTS W/CODES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wcodes) article.

OXYGEN SENSOR HEATING ELEMENT

On models with oxygen sensor heating elements, disconnect 3-wire connector at oxygen sensor. Measure resistance between White wire terminals on sensor side of connector. Resistance should be 3.5-14 ohms at 68°F (20°C). If resistance is not 3.5-14 ohms, replace oxygen sensor.

THROTTLE POSITION (TP) SENSOR

1. Install jumper wires to enable connection of a DVOM in parallel between TP sensor harness connectors. Connect DVOM positive lead to Dark Blue wire terminal. Connect negative lead to Black wire terminal. (Scheme 1)
2. Turn ignition on, engine off. Slowly depress accelerator pedal. Signal voltage should gradually change from less than one volt at closed throttle to about 5.0 volts at wide open throttle position. If reading is not as specified, replace TP sensor.
3. TP sensor circuit malfunction should set a related trouble code. For further information, see the «TESTS W/CODES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wcodes) article. Also see TP SENSOR ADJUSTMENT in the «ADJUSTMENTS»(/pontiac/trans-sport/ii-1996-1999/remont/adjustments/#engine-adjustments) article.

Scheme 1

TRANSMISSION RANGE SWITCH

A problem in transmission range switch circuit will set related diagnostic trouble code. See the TESTS W/CODES article.

VEHICLE SPEED SENSOR (PM GENERATOR)

Disconnect vehicle speed sensor harness connector (located in transmission/transaxle). Place gear selector in Neutral. Raise vehicle drive wheels off the ground. Turn drive wheels by hand (more than 3 MPH). Measure AC signal voltage between sensor terminals. Voltage reading should vary from 0.1 to 0.5 volt AC as wheel is turned. If reading is not as specified, replace vehicle speed sensor. If a code is set, refer to the TESTS W/CODES article.

RELAYS

Note. To perform the following tests, use the WIRING DIAGRAMS article.

A/C Clutch Relay

See MISCELLANEOUS PCM/VCM CONTROLS .

Fuel Pump Relay

1. If a prolonged crank is required to start vehicle, fuel pump relay may be faulty. To verify, start engine. With engine running, disconnect oil pressure switch (fuel pump back-up circuit). If engine stalls, fuel pump relay is faulty. If vehicle continues to run, relay is okay. Check for other causes of prolonged crank.
2. To test fuel pump relay, disconnect fuel pump relay. Refer to «COMPONENT LOCATIONS»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests__component-locations) . Apply battery voltage and ground to fuel pump relay winding terminals (control and ground).
3. Using an ohmmeter, check continuity between fuel pump relay control and ground terminals. Continuity should exist. If continuity does not exist, fuel pump relay is defective.
4. To by-pass fuel pump relay on vehicle (fuel pump not operating), turn ignition off. Disconnect fuel pump relay connector. Using a fused jumper wire, connect fuel pump test connector to positive side of battery. Fuel pump should run.
5. If fuel pump runs, check for faulty connections to relay or replace defective relay. To locate fuel pump test connector, refer to «COMPONENT LOCATIONS»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests__component-locations) .

SOLENOIDS

Note. All PCM/VCM-controlled solenoids should have at least 20 ohms of resistance (except fuel injectors).

Canister Purge Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

Idle Air Control (IAC) Valve

See IDLE CONTROL SYSTEM under FUEL SYSTEM.

Torque Converter Clutch (TCC) Solenoid

See MISCELLANEOUS PCM/VCM CONTROLS .

FUEL DELIVERY

Note. For fuel system pressure testing, see the BASIC TESTING article.

Fuel Pressure Regulator (SFI)

Fuel pressure regulator is a vacuum-controlled diaphragm type, which uses manifold vacuum to modify fuel pressure to compensate for engine load fuel requirements. Connect fuel pressure gauge to fuel pressure service port. Start engine and note fuel pressure. Disconnect vacuum hose from fuel pressure regulator. Fuel pressure should increase 4-10 psi (.28-.70 kg/cm 2 ). If pressure does not increase 4-10 psi (.28-.70 kg/cm 2 ), check for presence of manifold vacuum at signal line. If vacuum is not present, check for kinked, cut or split vacuum hose or plugged throttle body vacuum port. If vacuum is present and no pressure change occurs, replace fuel pressure regulator.

Fuel Pump Oil Pressure Switch (Back-Up Circuit)

To test fuel pump oil pressure switch (fuel pump back-up circuit), start engine. With engine running, disconnect fuel pump relay. If engine stalls, fuel pump oil pressure switch is faulty. If vehicle continues to run, switch is okay.

See FUEL PUMP RELAY under MODULES, MOTORS, RELAYS & SOLENOIDS .

Fuel Pump Relay By-Pass Procedure

If fuel pump will not energize, relay may be by-passed to test fuel pump. Turn ignition off. Using a fused jumper wire, apply battery voltage to fuel pump test connector. Fuel pump should turn on. For fuel pump test connector location, refer to COMPONENT LOCATIONS .

SFI Fuel Injector(s)

Disconnect fuel injector harness connector. Measure resistance across injector terminals. Resistance should be as specified. See SFI FUEL INJECTOR RESISTANCE table.

SFI FUEL INJECTOR RESISTANCE

See ENGINE SENSORS & SWITCHES .

Note. If injectors are dirty, they should be cleaned using approved injector cleaning procedure before performing fuel INJECTOR BALANCE TEST.

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»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wo-codes) article.

1. Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" to "B" and "C" to "D". (Scheme 2) Resistance should be 40-80 ohms. If okay, go to next step. If resistance is not as specified, replace IAC valve.
2. Check resistance between IAC terminals "B" to "C" and "A" to "D". Resistance should be infinite. If resistance is not as specified, replace IAC valve.

Note. Functional testing of Idle Air Control (IAC) valve requires a bidirectional scan tool capable of cycling PCM/VCM output devices or a special IAC Driver and Noid Light Set (222L or J-37027). Text in TESTS W/CODES article may refer to Tech 1 tester, General Motor's bidirectional scan tool.

Scheme 2

IGNITION SYSTEM

Note. For basic ignition system checks, see the BASIC TESTING article.

Ignition Control Circuit

An open or short to ground in Ignition Control (IC) or by-pass circuit will cause PCM/VCM to turn on Malfunction Indicator Light (MIL) and confirm fault by setting a related trouble code. Refer to the TESTS W/CODES article.

Knock Sensor Circuit (Models Using External Spark Controller Module)

1. An open or short circuit on IC module control wire to PCM/VCM will cause a loss of 12-volt IC module signal. This will cause PCM/VCM to fully retard ignition timing.
2. If a scan tool is available, connect tester to Data Link Connector (DLC). Using a metal object, tap on engine next to knock sensor and note knock parameter. Knock should be indicated on scan tool.
3. If a scan tool is not available, backprobe PCM/VCM knock sensor signal terminal with a DVOM. With engine idling, 8-12 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at PCM/VCM terminal should drop to zero volts, and return to original voltage when knock signal ceases.
4. If voltage signal does not respond as described, check knock sensor-to-module-signal. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. See KNOCK SENSOR under «ENGINE SENSORS & SWITCHES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests) .

Knock Sensor Circuit (Models Using Knock Sensor With Internal Spark Controller Module)

1. An open or short circuit on knock sensor wire to PCM/VCM will set a related trouble code. A false detonation signal will not cause PCM/VCM to set a code.
2. If a scan tool is available, connect it to Data Link Connector (DLC). Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tool.
3. If a scan tool is not available, connect tachometer to engine. Start engine and hold RPM above idle. Using a metal object, tap on engine close to knock sensor. A noticeable decrease in engine RPM should occur. If no RPM decrease occurred, check knock sensor to PCM/VCM circuit.
4. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. See KNOCK SENSOR under «ENGINE SENSORS & SWITCHES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests) .

Linear EGR Valve (Digital Valve)

1. Install scan tool. Ensure transmission range switch is operating properly. See «ENGINE SENSORS & SWITCHES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests) . With engine at normal operating temperature, command EGR pintle position to zero percent. Increase engine speed to 2000 RPM. If scan tool reads actual EGR pintle position at greater than 3 percent, EGR valve is stuck open. Replace EGR valve.
2. If scan tool reads actual EGR pintle position at 3 percent or less, command a 25 percent position step increase (i.e. 0-25 percent, 25-50 percent, 50-75 percent, etc.). Observe MAP reading and actual EGR pintle position for 3 seconds. EGR should increase by about 25 percent position and MAP reading should also increase.
3. If actual EGR pintle position is stable and within 10 percent of desired EGR pintle position command after 2 seconds, go to next step. If actual EGR pintle position is not as specified, go to step 5).
4. MAP reading should have increased when EGR pintle responded. If MAP did not respond, check EGR passages and EGR valve for blockage. If MAP responded, set desired EGR pintle position to 100 percent. If EGR pintle position sets to 100 percent, EGR is okay. If not, replace EGR valve.
5. Turn engine off. Check EGR electrical circuit and connecting components. Turn ignition on, check for 5-volt reference voltage on harness connector terminal "D" (Gray wire). If 5-volt reference voltage is not present, check PCM/VCM. See «CONTROL UNIT»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests__control-unit) under COMPUTERIZED ENGINE CONTROLS. If circuits are okay, replace EGR valve.

Required Service

The PCV system may require service for obstructions if any of the following conditions exist

1. Rough Idle
2. Stalling or Low Idle Speed
3. Oil Leaks
4. Oil in Air Cleaner
5. Sludge in Engine

A leaking PCV valve or hose could cause

1. Rough Idle
2. Stalling
3. High Idle Speed

If engine idles roughly, check for clogged PCV valve and for plugged or broken PCV hoses BEFORE adjusting idle. Check for correct PCV valve application to ensure the correct valve is fitted. Replace PCV valve if required.

Checking PCV Valve Function

1. Remove PCV valve from rocker cover. Run engine at idle. Place thumb over open end of valve to check for vacuum. If there is no vacuum at valve, check for obstruction in manifold port, hoses or PCV valve. Repair or replace as necessary.
2. Turn engine off. Remove PCV valve. Shake valve and listen for rattle of check valve inside PCV valve. If a clear rattle is not heard, replace PCV valve.
3. Visually inspect valve for varnish or deposits that may make PCV valve sticky, restricted or incompletely seated. Replace if necessary.
4. Engine must be sealed for PCV system to function as designed. If leakage, sludging or dilution of oil is noted and PCV system is functioning properly, check engine for cause and repair as required to ensure PCV system will continue to function properly.
5. Since an engine operating without any crankcase ventilation can be damaged, it is important to replace PCV valve and air cleaner breather at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.

MISCELLANEOUS PCM/VCM CONTROLS

Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

TRANSMISSION

Note. To perform the following tests, use appropriate wiring diagram in the WIRING DIAGRAMS article.

Disconnect harness connector to TCC solenoid. Measure resistance between TCC solenoid terminals. Solenoid resistance should be 10-15 ohms at 68°F (20°C).

Note. Some solenoids have an internal pressure switch in series with solenoid winding and will not show continuity until transmission hydraulic pressure is applied.

Converter Lock-Up Signal At Transmission

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Disconnect converter clutch connector at transmission. Connect a test light across converter clutch harness terminals. Start engine and place transmission in Drive. Accelerate vehicle to 45 MPH and note test light.
3. If test light is not on, check solenoid power supply wire of harness for open or short to ground. Check ground circuit for open between harness connector and PCM/VCM. If harness is okay, see CONVERTER LOCK-UP SIGNAL FROM PCM/VCM.

Converter Lock-Up Signal From PCM/VCM

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Connect a test light to battery voltage. Touch TCC control driver terminal with test light. Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty PCM/VCM connector or PCM/VCM.

Warning Light Diagnosis

1. Perform On-Board Diagnostics (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the «BASIC TESTING»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing) 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»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing) 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.

A/C COMPRESSOR CLUTCH CONTROLS

To provide improved idle quality, improved Wide Open Throttle (WOT) performance and A/C system protection, the A/C compressor clutch is controlled by the PCM.

Refrigerant switches used are a low pressure cut-off switch (some models), and an A/C pressure sensor. The A/C compressor clutch relay is controlled by PCM according to information received from refrigerant switches and various other sensors. This allows the PCM to raise idle speed before engaging compressor clutch, and disable compressor clutch during WOT, incorrect refrigerant pressure, or if coolant temperature becomes excessive. PCM inhibits A/C compressor clutch operation with engine speed greater than 4500 RPM for 5 seconds, or when throttle angle exceeds 90 percent.

RELAY LOCATION

A/C COMPRESSOR CLUTCH RELAY LOCATION

Note. To help save diagnostic time, ALWAYS check for blown fuses or fusible links before proceeding with any testing. If fuses are blown, locate and repair short circuit before replacing fuses. Ensure all related relay and wire harness connections are clean and tight. Repair as necessary.

Description

When A/C is selected, a 12-volt signal is supplied to A/C request input of PCM. A/C compressor clutch relay is controlled through PCM. PCM monitors A/C refrigerant pressure. If A/C refrigerant pressure and engine operating conditions are within a specific calibrated acceptable range, PCM will enable A/C compressor relay. This is done by providing a ground path for A/C relay coil within PCM. When A/C compressor relay is enabled, battery voltage is supplied to A/C compressor clutch coil.

PCM will enable A/C compressor clutch whenever engine is running and A/C has been requested, unless

1. Throttle angle is greater than 90 percent.
2. A/C head pressure is greater than 414 psi (29.1 kg/cm 2 ).
3. A/C head pressure is less than 35 psi (2.5 kg/cm 2 ).
4. Ignition voltage is less than 10.5 volts.
5. Engine speed is greater than 4500 RPM for 5 seconds.
6. Engine coolant temperature is greater than 257°F (125°C).
7. Intake air temperature is less than 41°F (5°C).

Compressor Clutch Control Circuit Diagnosis

1. If On-Board Diagnostic (OBD) System Check has not been performed, see the «BASIC TESTING»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing) 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»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wcodes) 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).

COOLING FAN

The electric cooling fan is used for radiator and A/C condenser cooling. Cooling fan operates when A/C is on and when engine coolant temperature exceeds a specific value. One or more cooling fan relays may be used.

To help save diagnostic time, ALWAYS check for blown fuses or fusible links before proceeding with any testing. If fuses are blown, locate and repair short circuit before replacing fuses. Ensure all related relay and wire harness connections are clean and tight. Repair as necessary. See WIRING DIAGRAM for component, terminal and wire color identification.

SCAN TESTER

A variety of information is transmitted through Data Link Connector (DLC). This data is transmitted at a high frequency which requires a Tech 1 Scan Tester (94-00101A), appropriate cartridge kit and vehicle interface module kit, or other scan tester for interpretation. Several scan testers (scan tools) are available for diagnostic work. Scan testers other than Tech 1 scan tester will function and provide information for diagnostic work.

COOLING FAN RELAY LOCATION

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 .

Power for cooling fan motors is supplied through COOL FAN 1 Maxi-fuse (30-amp) and COOL FAN 2 Maxi-fuse (30-amp) in underhood electrical center. Cooling fan relays are energized when current flows from Maxi-fuses through relay coils, then to ground through Powertrain Control Module (PCM). No. 1 cooling fan relay control circuit is grounded for low speed operation. Both fan control circuits and all 3 relays are grounded for high speed fan operation.

During low speed fan operation, PCM supplies a ground path for No. 1 cooling fan relay. As a result, relay contacts close, allowing current to flow from COOL FAN 1 Maxi-fuse through relay coil to cooling fan No. 1 (left side). During low speed operation, ground path for cooling fan No. 1 is through cooling fan relay (5-pin) and cooling fan motor No. 2 (right side). This results in a series circuit with both fans operating at low speed.

During high speed fan operation, PCM supplies 2 ground paths for all 3 cooling fan relays. As a result, relay contacts close in all relays, allowing both cooling fan motors to operate at high speed. Both cooling fans are supplied current from both COOL FAN Maxi-fuses. Each cooling fan motor has a separate ground path when operating in high speed mode.

Cooling Fan Circuit Diagnosis

1. If Powertrain On-Board Diagnostic (OBD) System Check has not been performed, see the «BASIC TESTING»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing) 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»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wcodes) 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»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests__ac-compressor-clutch-controls) .
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»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests__ac-compressor-clutch-controls) . 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.

COMPONENT LOCATIONS

COMPONENT LOCATIONS

Cooling Fan System Wiring Diagram. Scheme 3

See also:
• BASIC TESTING
• TESTS W/CODES
• ADJUSTMENTS
• TESTS W/O CODES
• MODULES, MOTORS, RELAYS & SOLENOIDS
• IGNITION SYSTEM
• MISCELLANEOUS PCM/VCM CONTROLS
• COMPONENT LOCATIONS
• CONTROL UNIT
• A/C COMPRESSOR CLUTCH CONTROLS