Engine Control System & Engine Component Tests - 3.8L: Other Pontiac Firebird IV

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on PCM ground terminals. Use appropriate wiring diagram in the WIRING DIAGRAMS article to determine PCM 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 voltmeter lead to a good ground. Touch positive voltmeter lead to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If 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 PCM constant battery power terminals and ground. If battery voltage is not present, check PCM power supply fuse. If fuse is okay, check for open in power supply or PCM wiring.
2. Turn ignition switch to ON position. Using a voltmeter, check for battery voltage between PCM 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 PCM, or check for a defective ignition switch.
3. Connect voltmeter between ground and PCM start (crank) signal terminal. Turn ignition switch to the START position. Battery voltage should be present between PCM 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 PCM, or check for a defective ignition switch.

ENGINE SENSORS & SWITCHES

Note. For additional sensor testing specifications, see the SENSOR RANGE CHARTS article.

A/C PRESSURE SENSOR

A malfunction in A/C pressure sensor circuit will set a related diagnostic trouble code. For testing procedures, see the TESTS W/CODES - 3.8L article. For wiring schematics, see appropriate diagram in the WIRING DIAGRAMS article.

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 next step. 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 appropriate diagram in the WIRING DIAGRAMS article.

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

A malfunction in the camshaft position sensor circuit will set a related diagnostic trouble code. See testing procedures in the TESTS W/CODES - 3.8L article.

CLUTCH ANTICIPATE SWITCH

Disconnect clutch anticipate switch harness connector located on clutch pedal. Using an ohmmeter, check continuity between switch terminals. Continuity should be present. Depress clutch pedal to activate clutch anticipate switch. Continuity should not be present. For further testing procedures, see the TESTS W/CODES - 3.8L article.

CRANKSHAFT POSITION SENSOR

A malfunction in the crankshaft position sensor circuit will set a related diagnostic trouble code. For testing procedures, see the TESTS W/CODES - 3.8L article. To diagnose crankshaft position sensor, the following procedures can be used

1. If a scan tool is available, scan RPM parameter while cranking engine. If RPM is indicated, crankshaft position sensor is operating properly.
2. If scan tool 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. On all engines, 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.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

If a coolant sensor-related diagnostic trouble code is present, see the TESTS W/CODES - 3.8L article. An out-of-calibration sensor may not set a diagnostic trouble code. Use following procedure to test sensor calibration. Disconnect ECT sensor connector. Measure resistance between sensor terminals. Resistance should be high when engine is cold and drop as engine warms. See ECT SENSOR RESISTANCE VALUES table.

ECT SENSOR RESISTANCE VALUES (1)

ENGINE OIL LEVEL SENSOR

1. Diagnose and clear any diagnostic trouble code first. If code(s) is not present, go to next step.
2. Ensure engine oil level is up to full mark on dipstick. Ensure LOW OIL LEVEL light circuit is not faulty. If circuit is okay, go to next step.
3. Disconnect engine oil level sensor connector. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit (Pink wire) at sensor harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
4. Connect test light between ignition feed and ground circuit at oil level sensor harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
5. Using a voltmeter, check voltage between engine oil level input circuit and ground. Battery voltage should be present. If battery voltage is not present, go to step 8). If battery voltage is present, go to next step.
6. Turn ignition off. Reconnect oil level sensor connector. Disconnect PCM connector. Connect voltmeter between engine oil level input circuit (Brown wire) and battery positive. Observe voltage while turning ignition on. If battery voltage is present for at least 2 seconds, go to step 11). If battery voltage is not present, go to next step 8).
7. Turn ignition off. Disconnect PCM connector. Turn ignition on. Check engine oil level sensor input circuit (Brown wire) for an open or shorted circuit. If circuit is open or shorted, go to step 14). If circuit is okay, go to step 12).
8. Disconnect engine oil level sensor. Check engine oil level input circuit for short to power. If circuit is shorted, go to step 14). If circuit is not shorted, check for poor connection at PCM or oil level sensor connector, or damaged wiring harness.
9. Locate and repair open in ignition feed circuit to oil level sensor. After repairs, go to step 14).
10. Locate and repair open in ground circuit to oil level sensor. After repairs, go to step 14).
11. Replace engine oil level sensor and proceed to step 14).
12. Check for poor connections at PCM. Repair as necessary and proceed to step 14). If connections are okay, go to next step.
13. Replace PCM and proceed to next step.
14. Turn ignition on. Observe LOW OIL LEVEL level light. If light stays on for more than 3 seconds after ignition is turned on, repeat step 2).

FUEL TANK VAPOR PRESSURE SENSOR

Fuel tank vapor pressure sensor is located on fuel sending unit. Using DVOM, check resistance between sensor terminals. Resistance should be 90 ohms with fuel tank full or zero ohms with fuel tank empty.

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 the TESTS W/CODES - 3.8L article. 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 VALUES table. After vehicle has sat overnight, IAT sensor and coolant sensor should have close to the same resistance reading.

IAT SENSOR RESISTANCE VALUES (1)

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. If any trouble codes are present, see the TESTS W/CODES - 3.8L article.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

1. A malfunction in the MAP sensor circuit should set a related Diagnostic Trouble Code (DTC) in PCM memory. If a DTC is present, see the «TESTS W/CODES - 3.8L»(ref-20509) article. An out-of-calibration sensor may not set DTC. 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 7) If driveability condition improves, replace MAP sensor.
2. With ignition on and engine off, check MAP sensor parameter using a scan tool connected to Data Link Connector (DLC). Voltage should be as specified. See «MAP SENSOR VOLTAGE RANGE»(ref-20510-S24374689052001010200000) 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 7

MAP SENSOR VOLTAGE RANGE

MASS AIRFLOW (MAF) SENSOR

A malfunction in the MAF sensor circuit will set a related diagnostic trouble code. For testing procedures, see DTC P0101 in the TESTS W/CODES - 3.8L article. If driveability problems exist, MAF sensor failure is suspected and no DTC P0101 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 the TESTS W/CODES - 3.8L article.

OXYGEN SENSOR (O2S)

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 PCM 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 PCM. 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 the «TESTS W/CODES - 3.8L»(ref-20509) article.

PARK/NEUTRAL POSITION (PNP) SWITCH

1. Disconnect PNP switch harness connector. Connect ohmmeter between the PNP switch terminals. (Scheme 8) 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 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 PCM.

Scheme 8

POWER STEERING PRESSURE (PSP) SWITCH

1. If scan tool 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 tool 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 battery voltage on PSP switch harness from PCM. If battery voltage is not present, check for open or short to ground in harness between PSP switch connector and PCM.

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 9) 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 the ADJUSTMENTS - 3.8L article.

A malfunction in the TP sensor circuit should set a related Diagnostic Trouble Code (DTC). For further information, see the TESTS W/CODES - 3.8L article.

Scheme 9

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 fluctuate from about 0.1 to 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 PCM memory. If a code is set, refer to the TESTS W/CODES - 3.8L article for diagnosis.

Idle Air Control (IAC) 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 .

SOLENOIDS

Note. All PCM-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.

AIR By-Pass Valve Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

Canister Purge Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

EGR Control Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

FUEL DELIVERY

Note. For fuel system pressure testing, see the BASIC TESTING - 3.8L article.

Fuel Pressure Regulator

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.

Note. For further fuel pump circuit diagnosis, refer to appropriate FUEL SYSTEM test under NO-START DIAGNOSIS in the BASIC TESTING - 3.8L article.

1. Disconnect fuel pump relay connector. See «COMPONENT LOCATION»(ref-20510-S38681219142001010200000) 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 the 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.

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. Turn ignition off. Disconnect fuel pump relay connector. Using a fused jumper wire, connect jumper wire between fuel pump feed terminal and fuel pump relay ignition feed circuit.
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.

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 FUEL INJECTOR BALANCE TEST.

Oxygen Sensor

See ENGINE SENSORS & SWITCHES .

1. Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" and "B" (coil "B") and "C" and "D" (coil "A"). (Scheme 10) 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 noid light, or a scan tool capable of cycling PCM output devices (General Motors Tech 1).

Scheme 10

IGNITION SYSTEM

Note. For basic ignition system checks, see the BASIC TESTING - 3.8L article.

Ignition Control (IC) Timing Advance System

A malfunction in the IC circuit (formerly referred to as the EST circuit) will cause PCM to turn on Malfunction Indicator Light (MIL) and confirm fault by setting a related diagnostic trouble code. Refer to the TESTS W/CODES - 3.8L article.

Knock Sensor (KS) System Without KS Module

1. An open or short circuit on KS wire to PCM will set a related diagnostic trouble code. A false detonation signal will not cause PCM to set a code.
2. If a scan tool is available, connect it to the DLC. Tap on engine next to knock sensor and note KNOCK parameter. Knock should be indicated on scan tool.
3. If a scan tool is not available, connect tachometer to engine. Start engine and hold RPM above idle. Using a metal object, tap on engine close to knock sensor. A noticeable decrease in engine RPM should occur. If no NOTICEABLE RPM decrease occurred, check knock sensor-to-PCM circuit.
4. On vehicles 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»(ref-20510-S35905847242001010200000) .

Knock Sensor (KS) System With KS Module

1. An open or short circuit on KS wire to PCM will cause a loss of 12-volt KS module signal. This will cause PCM to fully retard ignition timing.
2. If scan tool is available, connect it to the DLC. Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tool.
3. If scan tool is not available, connect a DVOM to PCM KS 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 PCM 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 module. 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»(ref-20510-S35905847242001010200000) .

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.

EXHAUST GAS RECIRCULATION

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, digital and linear EGR. See EGR SYSTEM IDENTIFICATION table.

EGR SYSTEM IDENTIFICATION

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. Apply vacuum with 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.

Linear EGR Valve

A malfunction in the EGR circuit will set a related diagnostic trouble code. See the TESTS W/CODES - 3.8L article.

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.

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 PCM-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 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.

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.

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 rough, 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.

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 correct coolant temperature without setting a Diagnostic Trouble Code (DTC). This could result in hot light turning on without having an overheating condition. It could also result in engine overheating without hot light turning on. Check coolant sensor temperature-to-resistance values in the SENSOR RANGE CHARTS article.

Hot light is powered by the 10-amp I/P IGN fuse. Light will turn on when PCM provides a ground for the circuit. If circuit grounds between light and PCM, light will illuminate any time 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 I/P IGN fuse. Faulty instrument cluster bulb. Open circuit between fuse and hot light.
2. Backprobe PCM hot light driver terminal with a test light to battery voltage. Turn ignition on. If test light does not illuminate, PCM terminal connection is bad or PCM is faulty. If test light illuminates, turn ignition off. Disconnect PCM connectors. Jumper PCM connector hot light driver harness terminal to ground. Turn ignition on. If hot light does not illuminate, check for open circuit between hot light and PCM. If all circuits are okay and power is available to light, replace instrument cluster.
3. Start engine. If hot light goes off, no problem is evident. If hot light is on, turn ignition off. Disconnect PCM connector. Probe PCM hot light driver harness terminal with a test light to battery voltage. If test light does not illuminate, replace PCM. If test light illuminates, repair short to ground in hot light driver circuit. If circuit is okay, replace instrument cluster.

TRANSMISSION

Note. Computerized transmission controls are also covered in greater detail in the AUTO TRANS DIAGNOSIS article. For component circuit ID see appropriate wiring diagram in the WIRING DIAGRAMS article.

Converter Clutch Solenoid

Disconnect harness connector to Torque Converter Clutch (TCC) solenoid. Measure resistance between appropriate TCC solenoid terminals. Solenoid resistance should be greater than 20 ohms.

Note. Some solenoids may 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.

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 appropriate converter clutch harness terminals. Start engine and place transmission in Drive. Accelerate vehicle to 45 MPH and note test light.
3. If test light is off, check solenoid power supply wire of harness for open or short to ground. Check ground circuit for open between harness connector and PCM. If harness is okay, see CONVERTER LOCK-UP SIGNAL FROM PCM.

Converter Lock-Up Signal From PCM

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

A/C COMPRESSOR CLUTCH CONTROLS

Note. For specific A/C clutch circuit testing, see A/C CLUTCH CIRCUIT DIAGNOSIS test.

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

For proper control of cooling fans, A/C compressor clutch and Idle Air Control (IAC) valve, a refrigerant pressure sensor is used. PCM uses signal provided by sensor to monitor high and low side refrigerant pressures. If PCM detects a fault in refrigerant pressure circuit, A/C compressor clutch will be disabled.

The A/C compressor clutch relay is controlled by PCM. This allows PCM to raise idle speed before engaging compressor clutch, or disable compressor clutch during WOT, high engine RPM, high power steering loads and hot engine restarts. PCM also disables compressor clutch if coolant temperature becomes excessive.

Note. See appropriate diagram in WIRING DIAGRAMS article for terminal and wire color ID. For component location, see COMPONENT LOCATION

A/C COMPRESSOR CLUTCH RELAY LOCATION

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

ELECTRIC COOLING FANS

Note. For specific electric cooling fan testing, see the ELECTRIC COOLING FAN CIRCUIT DIAGNOSIS test under CIRCUIT DIAGNOSIS TESTS. For component locations, see COMPONENT LOCATION . For terminal/wire color ID, see the WIRING DIAGRAMS article

All FWD and some RWD vehicles use an electric cooling fan. The electric cooling fan is used for radiator and A/C condenser cooling. Cooling fan operates when A/C is on and when engine coolant temperature exceeds a specific value. One or more cooling fan relays may be used. For cooling fan relay location, see COOLING FAN RELAY LOCATION table.

COOLING FAN RELAY LOCATION

To help save diagnostic time, ALWAYS check for blown fuses or fusible links before proceeding with any testing. If fuses are blown, locate and repair short circuit before replacing fuses. Ensure all related relay and wire harness connections are clean and tight. Repair as necessary. For component location, and terminal and wire color identification, see the ENGINE COOLING FAN article in the ENGINE COOLING section.