Engine Controls - System/component Tests - v6 Chevrolet Caprice IV

INTRODUCTION

Before testing separate components or systems, perform all procedures listed in BASIC TESTING article in this section. Since many computer-controlled and monitored components will set a diagnostic trouble code if they malfunction, it is also recommended that self-diagnosis be performed. See appropriate TESTS W/CODES article in this section.

A & C CHART REFERENCES

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 to isolate wiring harness shorts or opens. The following table provides the location of commonly used diagnostic information. These former "A" and "C" charts are now written in text and inserted into the appropriate location in the new Engine Performance workflow. To familiarize yourself with the Engine Performance workflow, see AA - USING THIS SECTION article in this section.

A & C CHART REFERENCE

BODY CODE IDENTIFICATION

BODY CODE IDENTIFICATION

Scheme 36

1. Install Tech 1 scan tester. Disconnect boost control solenoid harness connector. Turn ignition on, engine off. Connect test light between boost control solenoid harness connector terminal "A" and ground. (Scheme 36) Test light should illuminate. If test light illuminates, go to step 3). If test light did not illuminate, go to next step.
2. Check 15-amp engine control fuse. If fuse is blown, check for a shorted circuit between fuse and boost control solenoid. If fuse is okay, check for an open circuit between fuse and boost control solenoid. (Scheme 36) Repair as necessary.
3. Connect test light between boost control solenoid harness connector terminals "A" and "B". (Scheme 36) Test light should not illuminate. If test light did not illuminate, go to next step. If test light illuminated, go to step 5).
4. Turn ignition off. Disconnect PCM Green connector. Turn ignition on. If test light illuminated, check for shorted circuit between PCM terminal GC9 and boost control solenoid terminal "B". (Scheme 36) If test light did not illuminate, replace PCM.
5. Using Tech 1 scan tester, select boost control output test under miscellaneous tests. Turn on boost control solenoid using Tech 1. Test light should illuminate when boost control solenoid is turned on. If test light did not illuminate, go to next step. If test light illuminated, go to step 7).
6. Connect a test light to battery positive. Using test light, backprobe PCM terminal GC9. Turn on boost control solenoid using Tech 1. If test light illuminated, check for open in circuit between PCM terminal GC9 and boost control solenoid terminal "B". (Scheme 36) If test light did not illuminate, check for poor connection at PCM or for a faulty PCM.
7. Reconnect boost control solenoid harness connector. Disconnect boost signal hose between boost control solenoid and by-pass valve actuator. Connect vacuum gauge and read boost signal from solenoid. With transmission in Park, start and idle engine. If vacuum is not present, check circuit for poor connections to solenoid or for faulty solenoid. If vacuum was present, go to next step.
8. Using Tech 1 scan tester, turn off boost control solenoid. Observe vacuum gauge. Vacuum reading should be approximately 15 in. Hg. If vacuum reading is as specified, go to next step. If vacuum reading is not as specified, check for restriction in boost source to boost control solenoid. If restriction is not found, replace boost control solenoid.
9. Check for restriction in boost signal hose between boost control solenoid and by-pass valve actuator. Repair as necessary. If restriction is not found, boost control solenoid is functioning normally.

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on control unit ground terminals. Use appropriate wiring diagram in WIRING DIAGRAMS article to determine ECM ground terminals. Resistance to ground should be zero ohms. If reading is other than zero ohms, repair open to circuit ground.
2. Using a DVOM, 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 one volt or more, check for open, corroded or loose connection on ground lead.

Power Circuits

1. Using a voltmeter, check for battery voltage between control unit constant battery power terminals and ground. If battery voltage is not present, check control unit power supply fuse. If fuse is okay, check for open in power supply or control unit wiring.
2. Turn ignition switch to the ON position. Using a voltmeter, check for battery voltage between control unit ignition power terminals and ground. If battery voltage is not present, check power supply fuse(s). If fuse is okay, check for an open in wiring between fuse and control unit, or check for a defective ignition switch.
3. Connect voltmeter between ground and control unit start (crank) signal terminal. Turn ignition switch to the START position. Battery voltage should be present between control unit start terminal and ground ONLY when ignition switch is in the START position.
4. If voltage is not present, check fuse(s). If fuse is okay, check for an open in wiring between fuse and control unit, or check for a defective ignition switch.

ENGINE SENSORS & SWITCHES

Note. For additional sensor testing specifications, see SENSOR RANGE CHARTS article in this section.

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.
3. 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.

A/C PRESSURE SENSOR

A malfunction in A/C pressure sensor circuit will set a related diagnostic trouble code. For testing procedures, see appropriate TESTS W/CODES article in this section. For wiring schematics, see mini-schematics under A/C CLUTCH (C-10) & ELECTRIC COOLING FAN (C-12) under MISCELLANEOUS CONTROLS .

A/C PRESSURE SWITCH

1. Connect A/C pressure gauges to system and start engine. Note high and low pressure readings. If pressures are normal, go to step 2). If pressures are less than normal, check system for leaks. Evacuate and recharge as necessary. If pressures are high, check for system overcharge, overheating or mechanical failure in refrigerant delivery system.
2. Disconnect high and low pressure switches. Install jumper across each switch harness connector to allow A/C system to function normally. Using an ohmmeter, check continuity between pressure switch terminals.
3. Continuity should be present on both high and low switches (if equipped). If continuity is not present, replace A/C pressure switch. For wiring schematics, see mini-schematics under A/C CLUTCH (C-10) & ELECTRIC COOLING FAN (C-12) under «MISCELLANEOUS CONTROLS»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6__miscellaneous-controls) .

BRAKE SWITCH

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

CAMSHAFT POSITION SENSOR (C(3)I SYSTEM)

A malfunction in the camshaft position sensor circuit will set a related diagnostic trouble code. For testing procedures, see appropriate TESTS W/CODES article in this section.

COOLANT TEMPERATURE SENSOR (CTS)

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

CTS RESISTANCE VALUES

CRANKSHAFT SENSOR

A malfunction in the crankshaft sensor circuit will set a related diagnostic trouble code. For testing procedures, see appropriate TESTS W/CODES article in this section.

To diagnose crankshaft sensor, the following procedures can be used

1. If a scan tester is available, scan RPM parameter while cranking engine. If RPM is indicated, crankshaft position sensor is operating properly.
2. If scan tester is not available, disconnect crankshaft position sensor harness connector. Set ohmmeter to 2-k/ohm position, and measure resistance across sensor terminals. Resistance should be 800-1200 ohms.
3. Set voltmeter on the 2-volt AC scale. Crank engine and measure output voltage across sensor terminals. Voltmeter reading should be .8-1.4 volts. If resistance reading is not as specified or sensor does not produce the specified output voltage reading, repair faulty wiring or faulty crankshaft position sensor.

DUAL CRANK (COMBINATION) SENSOR (C(3)I)

This test should only be performed if vehicle will not start, injectors will not pulse and spark plugs will not fire. This simulates a dual crank sensor signal. If spark and injector pulse occur, dual crank sensor or sensor connections are bad.

1. Turn ignition off. Disconnect No. 6 spark plug wire from coil tower. Install Spark Tester (ST-125) to coil tower. Install spark plug wire to spark tester.
2. Connect injector test light to any injector connector. Connect jumper wire across dual crank sensor connector terminals "A" and "B". (Scheme 37)or (Scheme 38). Turn ignition on, engine off ( DO NOT crank engine).
3. Using a test light connected to ground, momentarily touch dual crankshaft sensor terminal "A". Note injector test light and spark tester. Test light should blink and spark should be present at spark tester. NOTE: Repeatedly grounding terminal "A" at dual crank sensor or terminals "C" and "B" at C(3)I module may cause engine to flood.
4. If spark was present and test light came on, check for poor connection at dual crank sensor terminal. If connections are okay, replace faulty dual crank sensor. If there was no spark and test light did not come on, check for poor connection at C(3)I module or replace faulty C(3)I module.

Scheme 37

Scheme 38

INTAKE AIR TEMPERATURE (IAT) SENSOR

IAT sensor may also be referred to as a Manifold Air Temperature (MAT) sensor. If a IAT sensor related code is present, see appropriate TESTS W/CODES article in this section. An out-of-calibration sensor may not set a diagnostic 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. After vehicle has sat overnight, MAT sensor and coolant sensor should have close to the same resistance reading.

IAT SENSOR RESISTANCE

KNOCK SENSOR (KS)

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 DVOM between sensor terminal and ground. Set voltmeter to 2-volt AC scale. 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 under IGNITION SYSTEM. Also see Code 43 in appropriate TESTS W/CODES article in this section.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR (C-1)

1. A malfunction in the MAP sensor circuit should set a related diagnostic trouble code in ECM memory. If a code is present, see appropriate TESTS W/CODES article in this section. An out-of-calibration sensor may not set a diagnostic 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. (Scheme 39) If driveability condition improves, replace MAP sensor.
2. With ignition on and engine off, check MAP sensor parameter using a scan tester connected to the ALDL connector. Voltage should be as specified. See «MAP SENSOR VOLTAGE RANGE»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6) table. If MAP sensor voltage is as specified, go to step 3). If voltage is not as specified, check for 5-volt reference supplied to sensor. Check harness integrity. If no problems are evident, replace MAP sensor.
3. Using a hand-held vacuum pump, apply 10 in. Hg to MAP sensor, and note voltage change. Voltage should drop about 1.2-2.3 volts less than as specified in table. If voltage is not as specified or voltage reading does not immediately follow vacuum change, MAP sensor is faulty.

Scheme 39

MAP SENSOR VOLTAGE RANGE

MASS AIRFLOW (MAF) SENSOR (3.3L & 3.8L)

A malfunction in the MAF sensor circuit will set a related diagnostic trouble code. For testing procedures, see Code 34 in appropriate TESTS W/CODES article in this section. If driveability problems exist, MAF sensor failure is suspected and no Code 34 is present, disconnect MAF sensor connector. If driveability improves, replace MAF sensor.

MANIFOLD AIR TEMPERATURE (MAT) SENSOR

MAT sensor may also be referred to as an Intake Air Temperature (IAT) sensor. See INTAKE AIR TEMPERATURE (IAT) SENSOR . A malfunction in the MAT sensor will set a related diagnostic trouble code. For testing procedures, see appropriate TESTS W/CODES article in this section.

OXYGEN SENSOR

1. Start engine and warm to operating temperature. Disconnect oxygen sensor. Connect a DVOM between lead of oxygen sensor and ground. Place DVOM on the 2-volt scale. Voltmeter reading should increase to greater than .8 volt.
2. Using another DVOM on the 20-volt scale, connect voltmeter in series between the oxygen sensor wire from ECM and positive post of battery. Reading on voltmeter connected to oxygen sensor should decrease to a low voltage (less than .3 volt).
3. If a second DVOM is not available, install short jumper in oxygen sensor wire from ECM. Hold jumper in one hand and touch positive post of battery with other hand. This should cause oxygen sensor to produce less than .3 volt. For additional testing procedures, see appropriate TESTS W/CODES article in this section.

PARK/NEUTRAL POSITION (PNP) SWITCH (C-1)

1. Disconnect PNP switch harness connector. Connect ohmmeter between the PNP switch terminals. (Scheme 40) Continuity should be present only when gear shift selector is in Park or Neutral. If continuity is present, go to next step. If continuity is not present, check PNP switch adjustment or replace defective PNP switch.
2. With PNP switch connector disconnected, turn ignition on. Check for 12 volts on the Orange/Black wire of PNP switch harness. If 12 volts are not present, check for open or short to ground between switch harness connector and ECM.

Scheme 40

POWER STEERING PRESSURE (PSP) SWITCH (C-1)

1. If scan tester is available, scan power steering pressure switch status. Note status with engine running and wheels in straight-ahead position. Turn steering wheel to full left or right position and again note status. If status changed, power steering pressure switch is okay. If status did not change or scan tester is not available, go to next step.
2. Turn ignition off. Disconnect PSP switch harness connector. Connect ohmmeter between PSP switch terminals. Start engine. With no-load on power steering, continuity should not be present. Turn steering wheel to full left or right position. Continuity should now be present. If readings are not as specified, replace PSP switch.
3. With PSP switch connector disconnected and ignition on, check for 12 volts on switch harness from ECM. If 12 volts are not present, check for open or short to ground in harness between switch connector and ECM.

THROTTLE POSITION (TP) SENSOR

Install jumper wires to enable connection of a DVOM in parallel between TP sensor harness connectors. Connect DVOM positive lead to Dark Blue TP sensor signal wire terminal. Connect negative lead to Black, Black/Orange or Purple sensor ground wire terminal. (Scheme 41) Turn ignition on, with engine off. 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, adjust or replace TP sensor. See ADJUSTMENTS article in this section.

A malfunction in the TP sensor circuit should set a related diagnostic trouble code. For further information, see appropriate TESTS W/CODES article in this section.

Scheme 41

VEHICLE SPEED SENSOR (PM GENERATOR TYPE)

Disconnect vehicle speed sensor harness connector (located in transaxle). Place gear selector in Neutral. Raise vehicle drive wheels off the ground. Turn drive wheels by hand (greater than 3 MPH). Measure AC signal voltage between sensor terminals. Voltage reading should vary from 0.1-0.5 volt AC as the wheel is turned. If reading is not as specified, replace vehicle speed sensor.

VEHICLE SPEED SENSOR (LED TYPE)

A speed sensor or buffer malfunction should set a related diagnostic trouble code in ECM memory. If a code is set, refer to appropriate TESTS W/CODES article in this section for diagnosis.

SECONDARY AIR ELECTRIC AIR PUMP (3.4L VIN S)

Locate secondary AIR electric air pump under ABS hydraulic modulator, on left front of engine compartment. Disconnect 3-wire connector from electric air pump. Apply ground to terminal "C" (Black wire) of pump. Apply battery voltage with a fused jumper wire to terminal "A" (Red wire) of pump. Pump should run. If pump does not run, replace pump.

SECONDARY AIR ELECTRIC AIR PUMP (3.4L VIN X M/T)

Locate secondary AIR electric air pump under front right inner fender panel. Disconnect Orange and Black wire connector. Apply ground to Black wire terminal of air pump. Apply battery voltage with a fused jumper wire to Orange wire terminal of pump. Pump should run. If pump does not run, replace pump.

IDLE AIR CONTROL (IAC) MOTOR & IDLE SPEED CONTROL (ISC) MOTOR

See IDLE CONTROL SYSTEM.

A/C CLUTCH RELAY

See MISCELLANEOUS CONTROLS.

ELECTRIC AIR PUMP RELAY

See EMISSION SYSTEMS & SUB-SYSTEMS .

FUEL PUMP RELAY

See FUEL SYSTEM .

AIR BY-PASS VALVE SOLENOID

Note. All ECM-controlled solenoids should have at least 20 ohms of resistance when checked with positive ohmmeter lead connected to power supply terminal of solenoid and negative ohmmeter lead connected to ground terminal of solenoid. Some solenoids are equipped with internal diodes. On these solenoids, resistance values will differ if ohmmeter test leads are reversed.

See EMISSION SYSTEMS & SUB-SYSTEMS .

CANISTER PURGE SOLENOID

Note. All ECM-controlled solenoids should have at least 20 ohms of resistance when checked with positive ohmmeter lead connected to power supply terminal of solenoid and negative ohmmeter lead connected to ground terminal of solenoid. Some solenoids are equipped with internal diodes. On these solenoids, resistance values will differ if ohmmeter test leads are reversed.

See EMISSION SYSTEMS & SUB-SYSTEMS .

EGR CONTROL SOLENOID

Note. All ECM-controlled solenoids should have at least 20 ohms of resistance when checked with positive ohmmeter lead connected to power supply terminal of solenoid and negative ohmmeter lead connected to ground terminal of solenoid. Some solenoids are equipped with internal diodes. On these solenoids, resistance values will differ if ohmmeter test leads are reversed.

See EMISSION SYSTEMS & SUB-SYSTEMS .

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING article in this section.

Fuel Pressure Regulator (PFI)

1. Install fuel pressure gauge to fuel rail fuel pressure test fitting. Remove vacuum hose from fuel pressure regulator. Turn ignition on and note fuel pressure on gauge.
2. Start engine. Check for manifold vacuum at pressure regulator vacuum hose. If vacuum is not present, repair as necessary. Reconnect vacuum hose to pressure regulator and note fuel pressure on gauge. Compare first and second reading.
3. Fuel pressure reading should be 4-7 psi (.28-.49 kg/cm 2 ) less with vacuum hose installed. Fuel pressure should decrease as vacuum increases. If results are not as specified, replace fuel pressure regulator.

Fuel Pressure Regulator (TBI)

Fuel pressure regulator is mechanically controlled by internal spring pressure. Regulator is adjusted at factory and is not serviceable. If fuel pressure is too low, check fuel filter, fuel pump pressure and volume. If fuel pressure is too high, check for restricted fuel tank return line. If no faults are found and pressure is too high or too low, replace fuel pressure regulator.

Fuel Pump Relay (A-5)

1. Disconnect fuel pump relay connector. See «COMPONENT LOCATIONS»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6) at the end of this article to locate fuel pump relay. Apply battery voltage and ground to fuel pump relay winding terminals. To identify fuel pump relay terminals, see appropriate wiring diagram in WIRING DIAGRAMS article.
2. Using an ohmmeter, check for continuity between fuel pump relay power supply terminal and fuel pump drive terminal. Continuity should exist ONLY with relay energized. If relay does not test as indicated, replace relay.
3. To by-pass fuel pump relay (to test fuel pump and wiring when fuel pump is not energizing), see FUEL PUMP RELAY BY-PASS PROCEDURE below.

Fuel Pump Relay By-Pass Procedure

1. If fuel pump will not energize, relay may be by-passed to test fuel pump and related wiring. (Scheme 42) Turn ignition off. Disconnect fuel pump relay connector. Using a fused jumper wire, apply battery voltage to fuel pump test connector (located in engine compartment). For fuel pump test connector location, see «COMPONENT LOCATIONS»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6) at end of this article. (Scheme 135)- (Scheme 148).
2. If fuel pump runs and relay tests okay, check for faulty connections at relay. If fuel pump does not run, check for faulty wiring between relay and fuel pump or replace defective fuel pump.

Scheme 42

Oil Pressure Switch Fuel Pump Back-Up

With engine idling, disconnect fuel pump relay. Engine should continue to run through oil pressure switch back-up circuit. If engine stalls, check oil pressure switch and related wiring.

Fuel Injector(s)

Disconnect fuel injector harness connector. Measure resistance across injector terminals at each injector. Resistance should be as specified. See INJECTOR RESISTANCE SPECIFICATIONS table.

INJECTOR RESISTANCE SPECIFICATIONS (1)

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

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.

1. 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.
2. Follow manufacturer's instructions when installing adapter harness. Ignition should be turned off at least 10 seconds to complete ECM 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 tester 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.
7. If injectors are all okay, plug in harness connectors and review SYMPTOMS in TESTS W/O CODES article in this section.

See ENGINE SENSORS & SWITCHES .

IDLE AIR CONTROL (IAC) MOTOR

1. Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" and "B" (coil "B") and "C" and "D" (coil "A"). (Scheme 43) Resistance should be 40-80 ohms. If resistance is as specified, go to next step. If resistance is not as specified, replace IAC motor.
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 motor.

Note. Additional testing of Idle Air Control (IAC) motor requires an IAC motor actuator and node light, or a scan tester capable of cycling ECM output devices (General Motors Tech 1).

Scheme 43

IGNITION SYSTEM

Note. For basic ignition system checks, see BASIC TESTING article in this section.

Ignition Control (IC) Timing Advance System

1. A malfunction in the IC circuit (formerly referred to as the EST circuit) should set a related diagnostic trouble code. Start engine and warm to operating temperature. On vehicles equipped with a manual transmission, increase engine speed to about 2000 RPM. On vehicle equipped with an automatic transmission, slightly increase idle speed.
2. On all vehicles, ground "test" terminal "B" of ALDL connector. A noticeable change in engine speed should occur. If no change occurs, see DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section.

Knock Sensor (KS) System Without KS Controller (C-5)

1. An open or short circuit on the KS wire to the ECM will set a related diagnostic trouble code. A false detonation signal will not cause ECM to set a code.
2. If a scan tester is available, connect it to the ALDL connector. Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tester.
3. If a scan tester 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-ECM circuit.
4. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. Also, see KNOCK SENSOR (KS) under «ENGINE SENSORS & SWITCHES»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6__engine-sensors-switches) .

Knock Sensor (KS) System With KS Controller (C-5)

1. An open or short circuit on the KS wire to the ECM will cause a loss of the 12-volt KS controller signal. This will cause the ECM to fully retard ignition timing.
2. If a scan tester is available, connect it to the ALDL connector. Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tester.
3. If a scan tester is not available, connect a DVOM to the ECM ESC signal terminal. With engine idling, 12 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at ECM terminal should drop to zero volts, and return when knock signal ceases.
4. If signal does not respond as described, check knock sensor signal to KS controller. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. Also, see KNOCK SENSOR (KS) under «ENGINE SENSORS & SWITCHES»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6__engine-sensors-switches) .

AIR Pump (Belt-Driven)

Accelerate engine to approximately 1500 RPM and observe airflow from hoses. If airflow increases as engine is accelerated, pump is working properly. If airflow does not increase, check hoses, pump belt tension, leaky valves or defective air injection pump.

Check Valve

Detach check valve and blow through valve in direction of check valve flow (to cylinder head). Attempt to suck air back. Replace valve if airflow is allowed against the direction of flow.

Electric AIR Control By-Pass Valve (3.1L & 3.4L VIN X)

With engine at idle, check for at least 10 in. Hg to valve. Run engine at part throttle (less than 2000 RPM). Air should go into exhaust ports until system goes into closed loop, then divert the air to atmosphere. If this does not occur, check terminal harness connector to valve, check for short to ground in air solenoid harness or replace defective valve. Regardless of open or closed loop operation, air should always divert to atmosphere on heavy deceleration.

Electric AIR Pump Relay (3.4L VIN S)

1. Start engine. With engine operating in open loop, electric air pump should run and air should be coming out of electric air pump exhaust port.
2. If electric air pump is operating, allow engine to idle for at least 3 minutes. With vehicle in closed loop (or about 3 minutes after start), ECM should de-energize electric air pump relay and electric air pump should stop. If this does not occur, go to step 3). If air pump operates as described, relay is functioning properly.
3. Remove air pump relay from underhood electrical center. Air pump should stop. If air pump stops, go to step 4). If air pump does not stop, check circuit to air pump for a short to battery voltage.
4. Connect ohmmeter between relay terminals E1 (Brown wire) and E4 (Red wire). Connect ground to relay terminal E2 (Brown wire). Apply battery voltage to relay terminal E5 (Brown wire). Continuity should exist between terminals E1 and E4 of relay ONLY with relay energized. If relay does not test as indicated, replace relay.

EXHAUST GAS RECIRCULATION (C-7)

There are 3 types of EGR systems used: pulse width modulated backpressure (positive and negative) EGR with a control solenoid, pulse width modulated backpressure (positive and negative) EGR without a control solenoid, and digital EGR. See EGR SYSTEM IDENTIFICATION table.

EGR SYSTEM IDENTIFICATION

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.

EGR Control Solenoid (Normally Closed)

1. Disconnect EGR solenoid electrical harness connector and vacuum hoses. Connect a hand-held vacuum pump to solenoid vacuum source port. Connect vacuum gauge to solenoid EGR port. Pump up vacuum pump. Vacuum should not be present at port to EGR valve.
2. Activate EGR solenoid with a 12-volt power supply. Vacuum should now be present or registered at vacuum gauge. If vacuum is not present, check EGR solenoid resistance. Solenoid should have at least 20 ohms of resistance.

EGR Control Solenoid (Normally Open)

1. Disconnect solenoid harness connector. Install vacuum pump to vacuum source side of solenoid. Apply vacuum to solenoid. Vacuum should pass through when solenoid connector is disconnected.
2. Apply battery voltage and ground to solenoid terminals. With solenoid energized, apply vacuum to solenoid. Vacuum should not pass through solenoid. If results are not as specified, check EGR solenoid resistance. Solenoid should have at least 20 ohms of resistance.

Digital EGR Valve (3.1L, 3.4L & 3.8L)

1. If an EGR-related code is set, go to appropriate TESTS W/CODES article in this section for diagnosis. Start and allow engine to idle. With engine at normal operating temperature, disconnect digital EGR valve solenoid harness connector.
2. Using a 12-volt power source and a fused jumper wire, very quickly energize EGR solenoid No. 1 Blue wire terminal on EGR valve. (Scheme 44) RPM should drop slightly. Next, energize EGR solenoid No. 2 Brown wire terminal on EGR valve. RPM should drop slightly more than step 1). Energize EGR solenoid No. 3 Red wire terminal on EGR valve.
3. RPM should drop more than step 1) or 2). If RPM drops as indicated, EGR is okay. If RPM drop is not as indicated, check for plugged EGR passages or defective digital EGR valve. Check EGR solenoid resistance. See «DIGITAL EGR SOLENOID RESISTANCE»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6) table.

Note. For additional testing procedures, see appropriate TESTS W/CODES article in this section.

Scheme 44

DIGITAL EGR SOLENOID RESISTANCE (1)

Positive Backpressure EGR Valve

1. Place transmission in Park or Neutral. Set parking brake and block drive wheels. Connect tachometer. With engine running at normal operating temperature, run engine at 2000 RPM.
2. Disconnect vacuum hose from EGR valve and plug hose. EGR valve diaphragm should move down and engine RPM should increase. NOTE: On some engines with ECM-controlled solenoid, EGR vacuum is locked out in Park/Neutral and solenoid must be by-passed with vacuum supply hose.
3. Reconnect vacuum hose. EGR diaphragm should move up and engine RPM should decrease. A slight vibration of diaphragm plate may be noticed in backpressure EGR valves.
4. If engine RPM did not change and EGR diaphragm moved, the EGR valve is functioning properly. If engine RPM did not change and diaphragm did not move, remove EGR valve and apply 10 in. Hg to EGR vacuum signal port. EGR valve should not open.
5. If EGR valve opens, replace EGR valve. With vacuum still applied, direct a stream of air (15 psi maximum) into valve seat. EGR valve should open completely.
6. If air is not available, connect a short piece of hose over EGR valve seat. Connect vacuum pump to signal port. With thumb plugging intake port of EGR valve, operate vacuum pump while alternately blowing through hose and pausing.
7. With vacuum present at signal port, EGR valve should open while pressure is applied and should close when no vacuum is present.

Negative Backpressure EGR Valve

With engine off, disconnect vacuum hose to EGR valve. Connect vacuum pump to EGR and apply 10 in. Hg. EGR diaphragm should move up and stay up for 20 seconds. If valve does not operate as indicated, replace EGR valve.

FUEL EVAPORATION CONTROL (C-3)

Note. One of 2 types of solenoid is used: normally open or normally closed. See CANISTER PURGE SOLENOID IDENTIFICATION table.

CANISTER PURGE SOLENOID IDENTIFICATION

Canister Purge Solenoid (Normally Closed)

1. Disconnect canister purge solenoid harness connector and vacuum hose. Apply 10 in. Hg to ported intake manifold vacuum side of solenoid valve. If vacuum holds, go to next step. If vacuum does not hold, replace canister purge solenoid.
2. Using a 12-volt power source, energize canister purge solenoid. Vacuum should release. If vacuum does not release, replace canister purge solenoid. Solenoid resistance should be at least 20 ohms.

Canister Purge Solenoid (Normally Open)

1. Turn ignition ON. Apply vacuum to throttle body vacuum side of solenoid valve. If vacuum holds, go to next step. If vacuum does not hold, go to step 3).
2. Ground diagnostic terminal. If vacuum then drops, go to step 5). If vacuum still holds, go to step 6).
3. Disconnect solenoid electrical connector. Connect test light between connector terminals. If test light does not light, go to next step. If test light lights, check for poor connection. If connection is okay, replace defective solenoid.
4. Probe each terminal with a test light to ground. If test light does not light on either terminal, repair open in wire between fuse and solenoid. See WIRING DIAGRAMS article. If test light lights on one terminal only, repair open in wire between solenoid and solenoid driver terminal of ECM. See WIRING DIAGRAMS article. If test light lights on both terminals, repair short to voltage in wire between solenoid and solenoid driver terminal of ECM. See WIRING DIAGRAMS article.
5. Verify at least 10 Inch Hg (34kPa) of vacuum is available to purge solenoid at idle. If vacuum is as specified, no problem found at this time. If vacuum is not as specified, repair vacuum line or engine mechanical malfunction.
6. Disconnect solenoid electrical connector. If vacuum now drops, repair short to ground in wire between solenoid and solenoid driver terminal to ECM. See WIRING DIAGRAMS . If vacuum still holds, check hoses. If hoses are not restricted or blocked, replace purge solenoid.

Fuel Tank Pressure Control Valve

Apply approximately 15 in. Hg to fuel tank pressure control valve. The diaphragm should hold vacuum for at least 20 seconds. If fuel tank pressure control valve does not hold vacuum, replace tank pressure control valve.

Required Service

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

1. Rough idle.
2. Stalling or slow 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 or plugged or broken hoses BEFORE adjusting idle. Check 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. If a clear rattle is not heard, replace PCV valve.
3. Visually inspect valve for varnish or deposits which may make PCV valve operation sticky or restricted, or cause incomplete seating of valve. Replace if necessary.
4. An engine must be sealed for the PCV system to function as designed. If leakage, sludging or dilution of oil is noted and the PCV system is functioning properly, check engine for cause and repair as required to ensure PCV system will continue to function properly.
5. An engine operating without any crankcase ventilation can be damaged, so it is important to replace PCV valve and air cleaner breather (if equipped) at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.

Damper Door - Wax Pellet Actuator Check (TBI)

1. Remove air cleaner assembly from vehicle. Allow air cleaner assembly to cool to less than 40°F (4°C). Damper door should be closed to outside (cold) air.
2. Reinstall air cleaner assembly. Start engine and observe damper door. As air cleaner assembly warms up, wax pellet should expand, closing off hot air delivery and opening cold air delivery.
3. If door does not respond as indicated, ensure door is not binding and calibrated damper spring is installed properly.

MISCELLANEOUS CONTROLS

Note. Although some of the controlled devices listed here are not technically engine performance components, they can affect driveability if they malfunction.

HOT LIGHT OR COOLANT TEMPERATURE LIGHT

Note. These checks assume vehicle is not overheating. Verify proper operation of cooling system prior to diagnosing hot light. The coolant temperature sensor, in rare cases, may fail to indicate the correct coolant temperature without setting a diagnostic trouble code (Code 14 or 15). This could result in turning on the hot light without having an overheating condition. It could also result in engine overheating without turning on the hot light. Check coolant sensor temperature-to-resistance values in SENSOR RANGE CHARTS article in this section.

Hot light is powered by the 10-amp INDIC or GAGES fuse. Light will turn on when ECM provides a ground for the circuit. If circuit grounds between light and ECM, light will illuminate any time the ignition is turned on.

1. Turn ignition on with engine off (bulb test position). If hot light illuminates, go to step 3). If hot light does not illuminate, check the following and proceed to next step: 10-amp INDIC OR GAGES fuse. Faulty instrument cluster bulb. Open circuit between fuse and hot light.
2. Backprobe ECM hot light driver terminal with a test light to battery voltage. Turn ignition on. If test light does not illuminate, ECM terminal connection is bad or ECM is faulty. If test light illuminates, turn ignition off. Disconnect ECM connectors. Jumper ECM hot light driver harness terminal to ground. Turn ignition on. If hot light does not illuminate, check for open circuit between hot light and ECM. If all circuits are intact and power is available to light, instrument cluster must be replaced.
3. Start engine. If hot light goes off, no problem is evident. If hot light is on, turn ignition off. Disconnect ECM connector. Probe ECM hot light driver harness terminal with a test light to battery voltage. If test light is off, replace ECM. If test light is on, repair short to ground in hot light driver circuit. If no short is present, replace instrument cluster.

Converter Clutch Solenoid

Disconnect harness connector to Torque Converter Clutch (TCC) solenoid. Measure resistance between TCC solenoid terminals "A" and "D". Solenoid resistance should be greater than 20 ohms. (Scheme 45)- (Scheme 57).

Note. Some solenoids have an internal pressure switch in series with the solenoid winding and will not show continuity until that pressure switch is applied by transmission hydraulic pressure. (Scheme 45)- (Scheme 57).

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 terminals "A" and "D" of converter clutch harness. 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 ECM. If harness is okay, see CONVERTER LOCK-UP SIGNAL FROM ECM below.

Converter Lock-Up Signal From ECM

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. On some vehicles, this is terminal "F" of the ALDL connector. (Scheme 45)-22. Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty ECM connector or ECM.

Note. In the following schematics, Assembly Line Data Link (ALDL) connector is also referred to by manufacturer as Data Link Connector (DLC).

Scheme 45

Scheme 46

Scheme 47

Scheme 48

Scheme 49

Scheme 50

Scheme 51

Scheme 52

Scheme 53

Scheme 54

Scheme 55

Scheme 56

Scheme 57

Shift Light (Manual Transmission)

1. These tests assume a shift light problem exists. Use this procedure only if the light will not illuminate or illuminates all of the time.
2. Turn ignition on, with engine off. Note shift light. Shift light should not be on. If light is on, check for a short to ground between the bulb and the ECM, or for a bad ECM. (Scheme 58)
3. With ignition on and engine off, ground test terminal of ALDL connector. SERVICE ENGINE SOON light should start to flash and shift light should come on. If light comes on, go to next step. If SERVICE ENGINE SOON light does not flash, perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section.
4. If shift light does not come on, ground Tan/Black wire at appropriate ECM terminal using a jumper wire. See «SHIFT LIGHT CIRCUIT IDENTIFICATION»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6) table. If light still does not comes on, check for blown GAUGES fuse, blown bulb or open circuit between fuse and ECM. If light comes on when grounding terminal with a jumper wire, problem is a bad ECM connection or bad ECM.

SHIFT LIGHT CIRCUIT IDENTIFICATION

Scheme 58

A/C CLUTCH (C-10) & ELECTRIC COOLING FAN (C-12)

Note. For additional information on electric cooling fans, see appropriate ENGINE COOLING FANS article in the ENGINE COOLING Section.

1. Disconnect A/C clutch relay harness connector. Using proper mini-schematic and an ohmmeter, check continuity between A/C clutch relay winding terminals. See appropriate mini-schematic in «DIAGNOSTIC CHARTS»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6__diagnostic-charts) . Continuity should exist. Check continuity between clutch drive circuit terminals of relay. Continuity should not exist.
2. Using jumper wires, apply ground and battery voltage to relay winding of relay. Continuity should now exist between clutch drive circuit terminals of relay. Replace A/C clutch relay if readings are not as specified.

Cooling Fan System & Quad-Driver Check

1. Connect a test light to battery voltage. Touch test light probe to the cooling fan control driver terminal of the ECM. See appropriate mini-schematic in «DIAGNOSTIC CHARTS»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6__diagnostic-charts) . Disconnect coolant temperature sensor. This should set a code, causing ECM to engage cooling fan through relay. On some models, it may be necessary to jumper the coolant temperature sensor harness connectors. On some models, grounding the ALDL with the ignition on and engine off will cause the ECM to activate the cooling fan control driver (ground circuit).
2. If test light illuminates and cooling fan does not come on, check cooling fan relay, power circuits, cooling fan motor, and relay and fan motor ground circuits. If test light does not illuminate, problem is a faulty ECM connector or ECM. Clear diagnostic trouble code(s) from ECM memory after testing.
3. If cooling fan functions normally during testing but fails to operate under normal conditions, check ECM monitored inputs which affect cooling fan operation. These include the following: coolant temperature sensor, A/C request signal from A/C control switch and A/C pressure sensor, or pressure/temperature switch signals (if equipped).

Cooling Fan Relay

1. Disconnect cooling fan relay harness connector. Using an ohmmeter, check continuity of relay winding. See appropriate mini-schematic in «DIAGNOSTIC CHARTS»(/chevrolet/caprice/iv-1990-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v6__diagnostic-charts) . Continuity should exist. Check continuity across power delivery terminals of relay. With relay not energized, no continuity should exist.
2. With ohmmeter still attached to power delivery terminals of relay, apply battery voltage and ground to energize relay winding. Continuity should now be present between cooling fan relay power delivery terminals. Replace cooling fan relay if readings are not as specified.

Cooling Fan Motor

Disconnect cooling fan motor harness connector. Apply battery voltage to one of the fan motor terminals and jumper the other terminal to ground. Fan motor should activate. If fan motor does not activate, replace faulty fan motor.

Note. For a more specific system testing, refer to the following C-10 or C-12 diagnostic charts. If any chart other than a C-10 or C-12 chart is referenced, see appropriate TESTS W/CODES article in this section.

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 CKT (1 OF 2)(3.1L "J" BODY)

Cooling fan is ECM controlled based on inputs from coolant temperature sensor, A/C pressure sensor and Vehicle Speed Sensor (VSS). ECM grounds circuit No. 335, energizing cooling fan relay and turning on cooling fan. ECM grounds circuit No. 335 when coolant temperature is more than 228°F (109°C) or when A/C has been requested and A/C pressure sensor indicates high A/C pressure of about 200 psi (14.1 kg/cm 2 ). When cooling fan is turned on, ECM will keep fan energized at least 25 seconds or until vehicle speed exceeds 70 MPH. Also, if Code 14 or Code 15 is set or ECM is in fuel back-up mode, fan will run continuously.

Note. Test numbers refer to test numbers on diagnostic charts.

1. With diagnostic terminal grounded, cooling fan control driver will close, which should energize cooling fan relay.
2. If A/C fan control switch or circuit is open, fan will run whenever A/C is requested.
3. With A/C clutch engaged, A/C fan control switch should open when A/C high pressure exceeds about 200 psi (14.1 kg/cm 2 ). This signal should cause ECM to energize cooling fan relay. See CHART C-10.
4. Disconnecting A/C pressure sensor will cause Code 66 to set. After finishing this step, clear diagnostic trouble codes.

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 59

Scheme 60

CHART C-12 - COOLING FAN CKT (2 OF 2)(3.1L "J" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Battery voltage should be available to terminal No. 2 and circuit No. 650 when ignition is on.
2. Checks ability of ECM to ground circuit No. 335. Malfunction Indicator Light (MIL) should also be flashing at this point. If MIL is not flashing, see DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section.
3. If cooling fan does not run at this point, circuits No. 532 or 150 is open or cooling fan motor is faulty.

Scheme 61

CHART C-10 - A/C CLUTCH CONTROL CKT (1 OF 2)(3.1L "J" BODY)

A/C relay is energized when the ECM provides a ground path through circuit No. 459 when A/C switch is turned on. A/C clutch engagement is delayed .3 second after A/C is turned on. This allows IAC to adjust engine RPM for the additional load. ECM will temporarily disengage A/C clutch relay for calibrated times for one or more of the following conditions

1. Hot engine restart.
2. Wide Open Throttle (WOT) and TP sensor angle at 90 percent.
3. Power steering pressure high (open PSP switch).
4. Engine speed greater than 6000 RPM.
5. During IAC reset.

The A/C relay will remain disengaged if Code 66 is present, if A/C pressure is out of range, or when no A/C signal request is seen due to an open A/C switch or circuit. Diagnose basic A/C system.

Note. Test numbers refer to test numbers on diagnostic charts.

1. ECM will only energize A/C relay when engine is running. This test will determine if relay or circuit No. 459 is faulty.
2. This test determines if signal is reaching ECM on circuit No. 66 from A/C control panel. Signal should only be present when A/C or defrost mode has been selected.
3. If ECM sees a high power steering pressure signal, ECM will disengage A/C clutch.

Scheme 62

Scheme 63

CHART C-10 - A/C CLUTCH CONTROL CKT (2 OF 2)(3.1L "J" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Determines if pressure transducer is out of range, causing compressor clutch to be disengaged.
2. With engine stopped and field service mode activated, ECM should be grounding circuit No. 459, which should cause test light to come on.

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 64

CHART C-12 - COOLING FAN CKT (1 OF 2)(3.1L "L" BODY)

Cooling fan is ECM controlled based on inputs from coolant temperature sensor, A/C pressure sensor and Vehicle Speed Sensor (VSS). ECM grounds circuit No. 335, energizing cooling fan relay and turning on cooling fan. ECM grounds circuit No. 335 when coolant temperature is greater than 228°F (109°C) or when A/C has been requested and A/C pressure sensor indicates high A/C pressure of about 200 psi (14.1 kg/cm 2 ). When cooling fan is turned on, ECM will keep fan energized at least 25 seconds or until vehicle speed exceeds 70 MPH. Also, if Code 14 or Code 15 is set or ECM is in fuel back-up mode, fan will run continuously.

Note. Test numbers refer to test numbers on diagnostic charts.

1. With diagnostic terminal grounded, cooling fan control driver will close, which should energize cooling fan relay.
2. If A/C fan control switch or circuit is open, fan will run whenever A/C is requested.
3. With A/C clutch engaged, A/C fan control switch should open when A/C high pressure exceeds about 200 psi (14.1 kg/cm 2 ). This signal should cause ECM to energize cooling fan relay. See CHART C-10.
4. Disconnecting A/C pressure sensor will cause Code 66 to set. After finishing this step, clear diagnostic trouble codes.

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 65

Scheme 66

CHART C-12 - COOLING FAN CKT (2 OF 2)(3.1L "L" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. B+ should be available to terminal No. 2 and circuit No. 39 when ignition is on.
2. Checks ability of ECM to ground circuit No. 335. Malfunction Indicator Light (MIL) should also be flashing at this point. If MIL is not flashing, see DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section.
3. If cooling fan does not run at this point, circuit No. 702 or 150 is open or cooling fan motor is faulty.

Scheme 67

CHART C-10 - A/C CLUTCH CONTROL CKT (1 OF 2)(3.1L "L" BODY)

A/C clutch control relay is energized when ECM provides a ground path through circuit No. 459 and A/C switch is turned on. ECM delays A/C clutch engagement .3 second after A/C is turned on. This allows IAC to adjust engine RPM for additional load. ECM will temporarily disengage A/C clutch relay for calibrated times for one or more of the following conditions

1. Hot engine restart.
2. Wide Open Throttle (WOT) and TP sensor angle at 90 percent.
3. Power steering pressure high (open PSP switch).
4. Engine speed greater than 6000 RPM.
5. During IAC reset.

The A/C relay will remain disengaged when Code 66 is present, if A/C pressure is out of range, or when no A/C signal request is seen due to an open A/C switch or circuit. Diagnose basic A/C system.

Note. Test numbers refer to test numbers on diagnostic charts.

1. ECM will only energize A/C relay when engine is running. This test will determine if relay or circuit No. 459 is faulty.
2. This test determines if signal is reaching ECM on circuit No. 66 from A/C control panel. Signal should only be present when A/C or defrost mode has been selected.
3. If ECM sees a high power steering pressure signal, ECM will disengage A/C clutch.

Scheme 68

Scheme 69

CHART C-10 - A/C CLUTCH CONTROL CKT (2 OF 2)(3.1L "L" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Determines if pressure transducer is out of range, causing the compressor clutch to be disengaged.
2. With engine stopped and field service mode activated, the ECM should be grounding circuit No. 459, which should cause test light to illuminate.

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 70

CHART C-12 - COOLING FAN CKT (1 OF 2)(3.1L "W" BODY - CALIF.)

The primary and secondary cooling fans are controlled by ECM based on inputs from engine coolant temperature sensor, A/C control switches, vehicle speed and state of the A/C pressure sensor. ECM controls fans by grounding circuits No. 335 and/or No. 473, energizing fan relay. Battery voltage is then supplied to cooling fan motor.

ECM grounds circuits No. 335 and/or No. 473 when coolant temperature is greater than 223°F (106°C) or when A/C has been requested and pressure is about 200 psi (14.1 kg/cm 2 ). Once ECM turns on A/C relay, it will keep it on for a minimum of 30 seconds, or until vehicle speed exceeds 70 MPH (40 MPH for secondary fan). Primary fan will also run at all times if Code 14 or 15 is present or when ECM is in back-up mode.

Note. Test numbers refer to test numbers on diagnostic charts.

1. With diagnostic terminal grounded, cooling fan control driver(s) will close, energizing the fan control relay(s).
2. If A/C pressure is greater than 300 psi (21.2 kg/cm 2 ) or circuit is open, cooling fan will run whenever A/C is requested.
3. With A/C clutch engaged and A/C pressure sensor functioning properly, cooling fan should operate when pressure exceeds 200 psi (14.1 kg/cm 2 ). This signal should cause ECM to energize the cooling fan control relay(s).
4. This test determines if A/C pressure sensor is faulty or if ECM or circuitry is faulty.

Scheme 71

Scheme 72

CHART C-12 - COOLING FAN CKT (2 OF 2)(3.1L "W" BODY - CALIF.)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Battery voltage should be available to terminals No. 2 and 3 on each relay when ignition is turned on.
2. This test checks the ability of the ECM to ground circuit No. 335 (No. 473 secondary cooling fan relay). The Malfunction Indicator Light (MIL) should be flashing at this point. If MIL is not flashing, see DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section.
3. If cooling fan does not operate at this point, check for open in 11circuit No. 702 (No. 532 secondary fan) or circuit No. 150, or for faulty cooling fan motor(s).

Scheme 73

CHART C-12 - COOLING FAN CKT (1 OF 2)(3.1L "W" BODY - FED.)

Cooling fan is ECM controlled based on inputs from coolant temperature sensor, A/C control switches, A/C pressure sensor and Vehicle Speed Sensor (VSS). ECM grounds circuits No. 335 and/or 473, energizing cooling fan relay(s) and turning on cooling fan(s). ECM grounds circuits No. 335 and/or 473 when coolant temperature is more than 223°F (106°C) or when A/C has been requested and A/C pressure is about 200 psi (14.1 kg/cm 2 ). When cooling fan is turned on, ECM will keep fan energized at least 60 seconds or until vehicle speed exceeds 70 MPH for fan No. 1 or 40 MPH for secondary (No. 2) fan. If Code 14 or 15 sets, ECM is in back-up mode; primary (No. 1) fan will run continuously.

Note. Test numbers refer to test numbers on diagnostic charts.

1. With diagnostic terminal grounded, cooling fan control driver(s) will close, which should energize cooling fan relay(s).
2. If A/C pressure is greater than 300 psi (21 kg/cm 2 ) or circuit is open, fan will run whenever A/C is requested.
3. With A/C clutch engaged and A/C pressure sensor functioning properly, fan will run when pressure exceeds about 200 psi (14.1 kg/cm 2 ). This signal should cause ECM to energize cooling fan relay(s). See CHART C-10.
4. Determines if A/C pressure sensor is faulty, or if ECM or circuitry is faulty.

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 74

Scheme 75

CHART C-12 - COOLING FAN CKT (2 OF 2)(3.1L "W" BODY - FED.)

Note. Test numbers refer to test numbers on diagnostic charts.

1. B+ should be available to terminals No. 2 and 3 of each fan relay when ignition is on.
2. Checks ability of ECM to ground circuits No. 335 and 473. MALFUNCTION INDICATOR LIGHT (MIL) should also be flashing at this point. If MIL light is not flashing, see DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section.
3. If cooling fan does not run at this point, circuit No. 150, 532 or 702 is open, or cooling fan motor is faulty.

Scheme 76

CHART C-10 - A/C CLUTCH CONTROL CKT (1 OF 2)(3.1L "W" BODY - FEDERAL)

A/C relay is ECM controlled to delay A/C clutch engagement about .4 second after A/C is turned on. This allows IAC to adjust engine RPM for additional load. ECM also causes relay to disengage the A/C clutch during WOT when high power steering pressure is present or if engine is overheating.

ECM provides a ground path for circuit No. 459, energizing A/C clutch control relay. The A/C refrigerant pressure sensor is used to determine high and low pressure in the systems and also turns on the cooling fan when needed.

Note. Test numbers refer to test numbers on diagnostic charts.

1. ECM will only energize A/C relay when engine is running. This test will determine if relay or circuit No. 459 is faulty.
2. This test determines if signal is reaching ECM on circuit No. 66 from A/C control panel. Signal should only be present when A/C or defrost mode has been selected.
3. If ECM sees a high power steering pressure signal, ECM will disengage A/C clutch.

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 77

Scheme 78

CHART C-10 - A/C CLUTCH CONTROL CKT (2 OF 2)(3.1L "W" BODY - FEDERAL)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Determines if pressure transducer is out of range, causing compressor clutch to be disengaged.
2. With engine stopped and field service mode activated, the ECM should be grounding circuit No. 459, which should cause test light to illuminate.

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 79

CHART C-12A - COOLING FAN CKT (1 OF 3)(3.3L "A" BODY)

Power for cooling fan is supplied through a fusible link to terminal No. 30 on cooling fan relay. Cooling fan relay is energized when current flows to ground through a quad driver module inside ECM. Cooling fan relay is energized by ECM. ECM energizes relay through ECM terminal YE8 when coolant temperature reaches 212°F (100°C). Fan relay is also energized when A/C is requested.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Tech 1 scan tester output tests allows manual control of cooling fan.
2. Fan should be on when A/C is requested at idle.
3. Ensures ECM is receiving A/C request.

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 80

Scheme 81

CHART C-12B - COOLING FAN INOPERATIVE (2 OF 3)(3.3L "A" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Test light should be on because relay connector terminal No. 85 is fed directly from ignition.
2. Tech 1 scan tester miscellaneous function allows manual control of cooling fan relay. This checks circuit No. 535 and ECM.
3. Jumpering relay connector terminals No. 30 and No. 87 feeds fan motor directly. Fan motor should run.
4. Checks battery feed at cooling fan relay.

Scheme 82

CHART C-12C - COOLING FAN ON AT ALL TIMES (3 OF 3)(3.3L "A" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Removing relay interrupts current flow to fan motor, so fan should not be on.
2. Test light should be off with coolant temperature less than 212°F (100°C), no Code 14 or 15 set and A/C off.
3. If test light goes out when Black C-D connector is disconnected, ECM is faulty. Replace ECM.

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 83

CHART C-10 - A/C CLUTCH CONTROL CKT (1 OF 2)(3.3L "A" BODY)

A/C compressor clutch relay is ECM controlled. ECM provides a ground path for circuit No. 366 when A/C is requested. ECM will delay A/C compressor clutch engagement about .3 second after A/C is requested. This delay allows Idle Air Control (IAC) valve to adjust engine RPM for the additional load. ECM will temporarily disengage A/C compressor clutch for a predetermined time during WOT operation.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks A/C pressure cycling switch.
2. Verifies A/C request signal is present at ECM.

Scheme 84

Scheme 85

CHART C-10 - A/C CLUTCH CONTROL CKT (2 OF 2)(3.3L "A" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. 3) Test light indicates circuits No. 366, 639 and quad-driver "B" in ECM are okay.
2. 4) Test light indicates circuit No. 639 to A/C compressor clutch relay terminal No. 30 is okay.
3. 5) By-passes A/C compressor clutch relay to determine if relay, compressor clutch or clutch wiring is faulty.

Scheme 86

CHART C-12 - COOLING FAN CKT (1 OF 3)(3.3L "N" BODY)

Battery voltage to operate cooling fan motor is supplied to fan relay terminal No. 1. Battery voltage is supplied through ignition switch to fan relay terminal No. 2 to energize relay. When ECM grounds circuit No. 535, relay is energized and cooling fan is turned on. With engine running, ECM will energize cooling fan relay when A/C is requested and A/C pressure is more than 150 psi (10.5 kg/cm 2 ), coolant temperature is more than 212°F (100°C), or Code 14 or 15 is set.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Fan should be on when using Tech 1 scan tester to turn on quad driver inside ECM, providing a ground for fan relay.
2. Fan should be running with A/C requested and A/C pressure is greater than 150 psi (10.5 kg/cm 2 ).
3. Ensures ECM is receiving A/C request signal.

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 87

Scheme 88

CHART C-12A - COOLING FAN INOPERATIVE (2 OF 3)(3.3L "N" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Battery voltage should be present on terminals No. 1 and 2. Terminals No. 1 and 2 are connected directly to battery voltage.
2. Test light should be on when using Tech 1 scan tester to turn on quad driver inside ECM, allowing current to flow through fan relay coil.

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 89

CHART C-12B - COOLING FAN ON AT ALL TIMES (3 OF 3)(3.3L "N" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Cooling fan will run continuously if Codes 14, 15 and/or 66 are set.
2. Circuit No. 535 is grounded or ECM is faulty if test light illuminates.

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 90

CHART C-10 - A/C CLUTCH CONTROL CKT (3.3L "N" BODY)

A/C relay is ECM controlled. ECM provides a ground on circuit No. 459 when A/C is requested. ECM will delay A/C compressor clutch engagement about .3 second after A/C is requested. This allows IAC to adjust engine RPM for additional load.

ECM will temporarily disengage A/C compressor clutch for a pre-calibrated time during one or more of the following conditions: engine not running, Wide Open Throttle (WOT), engine coolant temperature greater than 246°F (119°C), high power steering pressure and IAC reset. A/C compressor clutch will remain disengaged if Code 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 test numbers on diagnostic charts.

1. Determines if A/C request signal is reaching ECM from A/C control panel.
2. Determines if ECM is attempting to energize A/C compressor clutch relay.
3. Checks for a faulty A/C compressor clutch relay.

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 91

Scheme 92

Scheme 93

CHART C-12 - COOLING FAN CKT (1 OF 2)(3.4L "F" BODY)

Cooling fan are ECM controlled based on inputs from coolant temperature sensor, A/C control switch, Vehicle Speed Sensor (VSS) and A/C pressure sensor. ECM grounds circuits No. 335, energizing cooling fan relay and turning on cooling fan. ECM grounds circuits No. 335 when coolant temperature is greater than 228°F (109°C) or when A/C has been requested and A/C pressure is about 240 psi (17.0 kg/cm 2 ). When cooling fan is turned on, ECM will keep fan energized at least 30 seconds or until vehicle speed exceeds 70 MPH.

Also, if Code 14 or Code 15 is set or ECM is in back-up mode, fan will run continuously.

Note. Test numbers refer to test numbers on diagnostic charts.

1. With diagnostic terminal grounded, cooling fan control driver(s) will close, energizing cooling fan relay(s).
2. If A/C pressure is greater than 240 psi (17.0 kg/cm 2 ) or circuit is open, fan would run whenever A/C is requested.
3. With A/C clutch engaged and A/C pressure sensor functioning properly, cooling fan should turn on when pressure exceeds about 200 psi (14.1 kg/cm 2 ). This signal should cause ECM to energize fan control relay(s). See CHART C-10.
4. This test determines if A/C pressure sensor is faulty, or if ECM or circuitry is faulty.

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 94

Scheme 95

CHART C-12 - COOLING FAN CKT (2 OF 2)(3.4L "F" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. B+ should be available to circuits No. 402 and 541 on relay when ignition is on.
2. Checks ability of ECM to ground ECM circuit No. 335. MALFUNCTION INDICATOR LIGHT (MIL) should also be flashing at this point. If MIL is not flashing, refer to DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section.
3. If fan does not turn on, circuit No. 150 or 409 is open, or cooling fan motor is faulty.

Scheme 96

CHART C-10 - A/C CLUTCH CONTROL CKT (3.4L "F" BODY)

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement after A/C is turned on. This allows ECM to adjust engine RPM before A/C clutch engages.

ECM will engage A/C clutch any time A/C has been requested unless any of following conditions exist

1. High coolant temperature.
2. Wide open throttle.
3. High engine RPM.
4. High A/C system pressure.
5. Low A/C system pressure.
6. Any A/C related diagnostic trouble code.

ECM determines when A/C has been requested when it receives a voltage signal from the A/C control head. If A/C refrigerant pressure is greater than 430 psi (30.2 kg/cm 2 ) of less than zero psi, A/C clutch will not engage.

Code 66 or 67 will set if A/C pressure sensor is faulty. Code 66 will set if A/C pressure sensor circuit is open or shorted to ground. Code 70 will set if signal circuit is shorted to voltage. Code 67 will set if A/C clutch engages and no pressure change is detected.

Note. Test numbers refer to test numbers on diagnostic charts.

1. This test checks ECM ability to control A/C clutch relay.
2. This test checks for grounded circuit No. 459 to ECM.

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 97

Scheme 98

Scheme 99

CHART C-12 - COOLING FAN CKT (1 OF 2)(3.4L "W" BODY)

The primary and secondary cooling fans are controlled by ECM based on inputs from coolant temperature sensor, A/C control switch, Vehicle Speed Sensor (VSS), and state of A/C refrigerant pressure sensor. ECM grounds circuit No. 335 and/or 473, energizing cooling relay(s) and turning on cooling fan(s). ECM grounds circuits No. 335 and/or 473, when coolant temperature is about 223°F (106°C), or when A/C has been requested and A/C pressure is about 200 psi (14.1 kg/cm 2 ). Once ECM turns on relay, it will keep it on for a minimum of 30 seconds or until vehicle speed exceeds 70 MPH (40 MPH for secondary fan).

If Code 14 or 15 is present, or if ECM is in back-up mode, primary cooling fan will run continuously.

Note. Test numbers refer to test numbers on diagnostic charts.

1. With diagnostic terminal grounded, cooling fan driver(s) will close, energizing cooling fan relay(s).
2. If A/C pressure is greater than 300 psi (21.1 kg/cm 2 ) or if circuit is open, cooling fan will run whenever A/C is requested.
3. With A/C clutch engaged and A/C pressure sensor functioning properly, cooling fan should come on when pressure exceeds 200 psi (14.1 kg/cm 2 ). This signal also causes ECM to energize cooling fan relay(s). See CHART C-10.
4. This test determines if A/C pressure sensor is faulty, or if ECM or circuitry is faulty.

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 100

Scheme 101

CHART C-12 - COOLING FAN CKT (2 OF 2)(3.4L "W" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. B+ should be available to circuits No. 250, 650, 1442 and No. 1444 on respective relay when ignition is on.
2. This test checks ECM's ability to ground circuit No. 335 (No. 473 on secondary fan). The Malfunction Indicator Light (MIL) should be flashing at this point. If MIL is not flashing, refer to DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section.
3. If cooling fan does not turn on at this point, circuit No. 150, 532 or 702 is open, or cooling fan motor(s) is faulty.

Scheme 102

CHART C-10 - A/C CLUTCH CONTROL CKT (1 OF 2)(3.4L "W" BODY)

A/C clutch control relay is ECM controlled to delay A/C clutch engagement about .4 second after A/C is turned on. This allows IAC to adjust engine RPM before clutch engages. ECM also disengages A/C clutch during WOT, when high power steering pressure is present, or if engine is overheating. The A/C clutch control relay is energized when ECM provides a ground path for circuit No. 459. The A/C pressure sensor is used to determine high and low pressure in system and also turns on cooling fan when needed.

Note. Test numbers refer to test numbers on diagnostic charts.

1. ECM will only energize A/C relay when engine is running. This test determines if relay or circuit No. 459 is faulty.
2. This test determines if signal is reaching ECM on circuit No. 66 from A/C control panel. Signal should only be present when A/C or defrost mode has been selected.
3. If ECM see a high power steering pressure signal, ECM will disengage A/C clutch.

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 103

Scheme 104

CHART C-10 - A/C CLUTCH CONTROL CKT (2 OF 2)(3.4L "W" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Determines if pressure transducer is out of range, causing compressor clutch to be disengaged.
2. With engine off and field service mode activated, ECM should ground circuit No. 459, which should cause test light to illuminate.

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 105

CHART C-12A - COOLING FAN CKT (1 OF 4)(3.8L "C" & "H" BODIES)

Power for fan motors comes through a 40-amp maxi-fuse element to terminal No. 1 on fan relays. Fan relays are energized when current flows to ground through quad driver inside PCM. Left fan has 2 speeds and right fan has one speed. PCM energizes low speed fan relay through PCM terminal GC4 when coolant temperature reaches 212°F (100°C) or when A/C is requested. PCM energizes high speed fan relay if A/C refrigerant pressure reaches 210 psi (14.8 kg/cm 2 ) or coolant temperature reaches 226°F (108°C).

Note. Test numbers refer to test numbers on diagnostic charts.

1. Using Tech 1 scan tester miscellaneous tests, low speed fan control will cause PCM to ground circuit No. 1269 and cooling fans should run at low speed.
2. Selecting high speed fans with Tech 1 scan tester allows control of circuit no. 1270 and high speed fan relay.
3. Jumpering A/C pressure switch harness connector will cause PCM to energize the high speed fan relay.

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 106

Scheme 107

CHART C-12B - COOLING FAN ON AT ALL TIMES (2 OF 4)(3.8L "C" & "H" BODIES)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks if circuit No. 1269 is shorted to ground, which would keep relay closed at all times.
2. Checks if circuit No. 1270 is shorted to ground. Continue to follow chart to isolate shorted circuit.
3. If test light is off after disconnecting PCM, ensure circuit No. 1269 is not shorted to B+. If circuit is not shorted, PCM is shorted internally.
4. If test light is off after disconnecting PCM, ensure circuit No. 1270 is not shorted to B+. If circuit is not shorted, PCM is shorted internally.

Scheme 108

CHART C-12C - COOLING FAN NO LOW SPEED FAN (3 OF 4)(3.8L "C" & "H" BODIES)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks for B+ at relay harness connector.
2. Jumpering relay terminals No. 1 and 4 by-passes relay, causing fans to run if fan motors and wiring are okay.
3. Grounding test terminal should cause PCM to ground circuit No. 1269. Test light should now glow if PCM is good and circuit No. 1269 is not open.
4. Checks for B+ and ground to fan motor. Test light on at this point indicates a faulty fan motor or motor connection.

Scheme 109

CHART C-12D - COOLING FAN NO HIGH SPEED FAN (4 OF 4)(3.8L "C" & "H" BODIES)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Test light should be on because harness terminals No. 1 and 2 have B+ with ignition switch on.
2. Jumpering harness terminals No. 1 and 4 by-passes relay. If fan runs, relay is faulty.
3. Checks circuit No. 1270 back to PCM. If circuit No. 1270 is okay, relay is faulty.

Scheme 110

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.

1. Codes 14 or 15 could mean coolant system or coolant temperature sensor operation is not normal, so fan(s) operation cannot be checked correctly.
2. 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.
3. 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 111

Scheme 112

CHART C-12B - COOLING FAN NO LOW SPEED (2 OF 5)(3.8L "E" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Test light should illuminate because harness terminal No. 2 has B+ with ignition switch on. Terminal No. 4 has B+ at all times.
2. Test light on validates relay "C" and circuits No. 1593, 1594, 1595and 804.
3. Jumpering relay "G" terminals No. 1 to 4, removing relay "C" and touching a test light to terminal No. 1 validates circuit up to relay "C". If light is off, open is in circuit No. 1593 or 1595 to front fan.
4. Test light on validates circuits No. 804 and 1594 to rear fan.

Scheme 113

Scheme 114

CHART C-12C-A - COOLING FAN NO HIGH SPEED REAR FAN (3 OF 5) (3.8L "E" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Test light should be on because harness terminal No. 5 has B+ with ignition switch on. Terminal No. 1 has B+ at all times.
2. Test light should be on with output tests, Fan 2 selected and cycled on with Tech 1 scan tester.
3. Jumpering harness terminals No. 1 and 4 by-passes relay. If fan runs, relay is faulty.
4. Test light on proves circuits No. 1594 and 804 are okay; fan motor is faulty.

Scheme 115

Scheme 116

CHART C-12C-B - COOLING FAN NO HIGH SPEED FRONT FAN (4 OF 5) (3.8L "E" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Test light should be on because harness terminal No. 5 has B+ with ignition switch on.
2. Test light on validates circuit No. 536 from PCM to relay "C".
3. Jumpering terminal No. 1 to 4 of relay "C" by-passes fan relay.
4. Test light on validates all circuits. If light is on, front fan motor is faulty. If light is off, problem is with ground circuit No. 804.

Scheme 117

Scheme 118

CHART C-12D - COOLING FAN ON AT ALL TIMES (5 OF 5)(3.8L "E" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Fans should not run when ignition is in OFF position.
2. Fans should not run when engine coolant temperature is less than 214°F (101°C).
3. Disconnecting A/C high side temperature sensor will disable BCM to PCM request due to A/C high side temperature.
4. Defines fan operation based on coolant temperature only.

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 119

CHART C-12A - COOLING FAN CKT (1 OF 6)(3.8L "W" BODY)

ECM uses 3 relays to control 2 cooling fans. Both fans run at low speed when ECM energizes cooling fan relay "B" when coolant temperature exceeds 214°F (101°C) or when A/C is requested. With ignition off, ECM will operate cooling fans at low speed if coolant temperature exceeds 230°F (110°F) and intake air temperature exceeds 102°F (39°F) at time key is turned off. ECM will keep fans energized at low speed with ignition off for up to 2 minutes or until coolant temperature falls to less than 210°F (99°C).

Both fans run at high speed when ECM energizes all 3 relays with coolant temperature exceeding 226°F (108°C) or when A/C refrigerant pressure is more than 200 psi (14.1 kg/cm 2 ). Cooling fans will not run at high speed with ignition off.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Codes 14 or 15 could mean cooling system or sensor is not operating normally; fan(s) operation cannot be checked correctly.
2. Selecting low speed fans under miscellaneous tests, fan control with Tech 1 scan tester causes ECM to energize fan relay "B" and operate fans at low speed.
3. Selecting high speed fans under miscellaneous tests, fan control with Tech 1 scan tester causes ECM to energize fan relays "B", "C", and "D", operating fans at high speed.
4. Cooling fans should run at low speed if an A/C mode is selected and ECM is receiving an A/C request signal.

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 120

Scheme 121

CHART C-12B - COOLING FAN NO LOW SPEED (2 OF 6)(3.8L "W" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Test light on verifies B+ to harness terminals No. 2 and 3 with ignition on.
2. Test light on verifies wiring for both fans.
3. Test light on verifies circuit No. 702 between fan relay "D" and left side fan and circuit No. 533 between left side fan and fan relay "B".
4. Test light on verifies circuit 532 between fan relay "D" and right side fan and circuit No. 150 between right side fan and ground.

Scheme 122

CHART C-12C-A - COOLING FAN NO HIGH SPEED RIGHT SIDE COOLING FAN (3 OF 6)(3.8L "W" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks B+ and ignition at relay harness connector.
2. Test light on verifies circuit No. 536 to cooling fan relay "C".
3. Jumpering terminals No. 3 to 5 in relay "C" by-passes relay and should cause fan to run if fan, wiring and motor are okay.
4. Checks for B+ and ground to fan motor. Test light on at this point indicates a faulty fan motor connection or motor.

Scheme 123

Scheme 124

CHART C-12C-B - COOLING FAN NO HIGH SPEED LEFT SIDE COOLING FAN (4 OF 6) (3.8L "W" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks ignition feed at relay "D" coil.
2. Ensures circuit No. 150 is not open between relay "D" and ground.
3. Isolates malfunction to ECM, wiring or fan relay "D".

Scheme 125

Scheme 126

CHART C-12D-A - COOLING FAN LOW SPEED FAN(S) ON AT ALL TIMES (5 OF 6) (3.8L "W" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Low speed cooling fans may run for up to 2 minutes with ignition off.
2. Verifies proper ECM control of fans.
3. Checks for circuit No. 535 shorted to ground or a faulty fan relay.
4. Checks for A/C request signal to ECM which would cause operation of low speed fans.

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 127

CHART C-12D-B - COOLING FAN HIGH SPEED FAN(S) ON AT ALL TIMES (6 OF 6) (3.8L "W" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Isolates problem to ECM control fault, faulty fan or relay or wiring problem.
2. Checks for proper operation of A/C head pressure switch.

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 128

CHART C-10 - A/C CLUTCH CONTROL CKT (3.8L "W" BODY)

A/C relay is PCM controlled to delay A/C clutch engagement .4 second after A/C is turned on, allowing IAC to adjust engine RPM before A/C clutch engages. PCM may apply A/C clutch during cranking to prevent A/C slugging. PCM also causes relay to disengage A/C clutch during Wide Open Throttle (WOT) operation. A/C relay is energized when PCM provides a ground path for circuit No. 366.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Compressor clutch should be not be engaged with A/C off.
2. Checks operation of A/C cycling switch.
3. Checks to see that A/C request signal is getting to PCM through circuit No. 67. If test light is off at this point indicates that circuit No. 67 is open between the cycling switch and PCM.
4. Checks for open in circuits No. 66, 257, 750 or A/C control switch.
5. Checks to see if PCM is controlling A/C clutch control relay.
6. Checks for battery voltage to A/C compressor relay through circuit No. 339.
7. By-passes relay to determine if problem is in relay or in circuit No. 59, A/C clutch coil, or ground.
8. "A/C Request" on Tech 1 should not display "YES" with A/C off.
9. This test locates source of false A/C request signal.
10. This step isolates A/C clutch from its control circuitry.
11. This test determines whether a faulty relay or relay control circuit is the cause of A/C clutch not engaging.

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CHART C-10 - A/C CLUTCH CONTROL CKT (4.3L "B" BODY)

When A/C switch is turned on, ignition voltage is supplied to the pressure cycling switch through the control head. If there is a sufficient A/C charge, the pressure cycling switch will be closed to complete the circuit to the ECM and to the A/C high pressure switch. If A/C head pressure is not too high, circuit would be completed to the A/C clutch coil.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks for short to ground in circuits No. 66, No. 67 or No. 1592 if fuse was open. Check for shorted compressor clutch coil. Check A/C system for further diagnosis of power feed circuit to the control head.
2. Check to determine if ECM is capable of detecting A/C status.
3. If A/C clutch engaged, check for 12 volt supply at ECM terminal B8. If voltage is present, a faulty connection exists at the ECM or ECM is faulty.
4. Before replacing control head, perform thorough A/C system diagnosis.

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See also:
• MISCELLANEOUS CONTROLS
• CTS RESISTANCE VALUES
• INTAKE AIR TEMPERATURE (IAT) SENSOR
• ENGINE SENSORS & SWITCHES
• DIAGNOSTIC CHARTS