Engine Controls - System/component Tests Geo Prizm pre-I

INTRODUCTION

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

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

Ground Circuit Checks

Check ground circuits to ECM for continuity to ground. 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 voltmeter reading is greater than one volt, check for open, corrosion or loose connection on ground lead. See appropriate wiring diagram in WIRING DIAGRAMS article.

Power Circuit Checks

Using DVOM, check power circuits to ECM for opens or shorts. See appropriate wiring diagram in WIRING DIAGRAMS article.

ECM CIRCUIT RESISTANCE

Coolant Temperature Sensor

Information not available from manufacturer.

COOLANT TEMPERATURE SENSOR RESISTANCE

Knock Sensor (Prizm GSi)

1. To check knock sensor resistance, use ohmmeter and measure resistance between sensor terminal and engine block. Knock sensor is located on rear of engine block and has a Black wire connector. Replace sensor if resistance is not 3300-4500 ohms.
2. To check knock sensor operation, remove connector from knock sensor. Connect voltmeter between sensor terminal and ground. Adjust voltmeter to 200 millivolts on AC scale.
3. Tap on engine block near knock sensor and note reading. Replace knock sensor if no reading is obtained.

Manifold Absolute Pressure (MAP) Sensor

1. The MAP sensor is located on firewall. With ignition on, check supply voltage from ECM to MAP sensor on designated wire terminal. See MAP SENSOR WIRE TERMINAL IDENTIFICATION table. Voltage should be approximately 5 volts.
2. Disconnect vacuum hose at MAP sensor and install hand-held vacuum pump. Turn ignition on. Check signal voltage at designated wire terminal of MAP sensor. See MAP SENSOR WIRE TERMINAL IDENTIFICATION table.
3. As vacuum reading changes, voltage should change. Reading should vary from approximately 1 to 1 1/2 volts at high vacuum and to 4 to 4 1/2 volts at low vacuum. Reading should change evenly as vacuum changes and will vary with altitude. See MAP SENSOR VOLTAGE SPECIFICATIONS table.

MAP SENSOR WIRE TERMINAL IDENTIFICATION

MAP SENSOR VOLTAGE SPECIFICATIONS

Mass Airflow (MAF) Sensor (Prizm GSi)

Information not available from manufacturer.

MAT SENSOR RESISTANCE SPECIFICATIONS

Manifold Air Temperature (MAT) Sensor (Prizm & Prizm GSi)

Information not available from manufacturer.

Oxygen Sensor

1. Start engine and warm to operating temperature. Pull back connector seal at oxygen sensor. Using a digital voltmeter with at least a 10-megohm input impedance, backprobe oxygen sensor connector.
2. With engine at idle, remove a large vacuum hose from intake manifold to create a large vacuum leak (without causing engine to stall). Voltage reading at oxygen sensor should drop. Reconnect vacuum line and voltage should increase. If voltage readings do not respond as specified, replace oxygen sensor.

Sub-Oxygen Sensor (Prizm GSi - Calif. Only)

1. Start engine and warm to operating temperature. Pull back connector seal at oxygen sensor. Using a digital voltmeter with at least a 10-megohm input impedance, backprobe oxygen sensor connector.
2. With engine at idle, remove a large vacuum hose from intake manifold to create a large vacuum leak (without causing engine to stall). Voltage reading at oxygen sensor should drop. Reconnect vacuum line and voltage should increase. If voltage readings do not respond as indicated, replace sensor.

Throttle Position Sensor (Except Prizm VIN 6)

Disconnect TPS electrical connection. Install proper thickness feeler gauge between stop screw and lever. Using ohmmeter, check continuity or resistance between designated terminals. Adjust or replace TPS if not within specification. See THROTTLE POSITION SENSOR (TPS) RESISTANCE table.

THROTTLE POSITION SENSOR (TPS) RESISTANCE

Throttle Position Switch (Prizm 4A-FE VIN 6)

1. With battery disconnected, disconnect switch electrical connection. Note TPS terminal identification. (Scheme 45) Install proper thickness feeler gauge between stop screw and lever. See THROTTLE POSITION SWITCH RESISTANCE table.
2. Using ohmmeter, check continuity or resistance between designated terminals. Adjust or replace switch if not within specification. See THROTTLE POSITION SWITCH RESISTANCE table.

THROTTLE POSITION SWITCH RESISTANCE

Scheme 45

Park/Neutral Switch (Prizm & Prizm GSi)

Information not available from manufacturer.

Note. Following procedure applies if Code 42 is stored in ECM memory or incorrect input from vehicle speed sensor is suspected.

Vehicle Speed Sensor

1. To check vehicle speed sensor only, remove instrument cluster. Connect ohmmeter across terminals No. 1 and 2 of vehicle speed sensor. (Scheme 46) Measure continuity while rotating speedometer. Replace speedometer if continuity does not exist 4 times per revolution.
2. To check vehicle speed sensor and circuit, check speedometer operation. If speedometer operates correctly, proceed to step 3). Repair or replace speedometer if speedometer is not operating properly.
3. Check cruise control operation. If cruise control operates correctly, proceed to step 7). If cruise control is not operating correctly, proceed to step 4).
4. Disconnect 14-pin connector from ECM, located in center of instrument panel, behind the console. Disconnect 10-pin connector from passenger's side of instrument cluster.
5. Using voltmeter, measure voltage from terminal No. 2 of vehicle speed sensor and ground. (Scheme 47) Turn on ignition and cruise control and note voltage. If voltage is greater than one volt, proceed to step 10). If no voltage was present, proceed to step 6).
6. Backprobe Purple/White wire at cruise control module 18-pin connector, located near right side of glove box. If reading is greater than one volt, repair open or short in Purple/White wires between ECM, cruise control module and instrument panel or instrument panel printed circuit. If no voltage was present, cruise control system must be checked.
7. Disconnect 10-pin connector from passenger's side on instrument panel. Disconnect cruise control module wiring connector. Using voltmeter, measure voltage from terminal No. 2 of vehicle speed sensor to ground. (Scheme 46) Turn ignition on and note voltage.
8. If voltage was greater than one volt, proceed to step 10). If no voltage was present, turn ignition off. Backprobe ECM 14-pin connector between Purple/White wire and ground. Turn ignition on and note voltage.
9. If voltage was greater than one volt, repair open or short in Purple/White wire between ECM, cruise control module and instrument panel or instrument panel printed circuit. If no voltage was present, check ECM.
10. Reinstall 10-pin connector on passenger's side of instrument cluster. Disconnect 10-pin connector from center of instrument cluster. Using ohmmeter, measure resistance from terminal No. 1 of vehicle speed sensor to ground. (Scheme 46)
11. If resistance is greater than 3 ohms, repair Brown ground wire between instrument cluster and ground. If resistance is less than 3 ohms, replace speedometer head.

Note. Following procedure applies if Code 24 is stored in ECM only (not transaxle Electronic Control Unit (ECU) on 4-speed applications) or when incorrect input from vehicle speed sensor is suspected.

Scheme 46

CIRCUIT OPENING RELAY & EFI RELAY

1. Circuit opening relay and EFI relay are located behind center console of instrument panel. Disconnect electrical connector.
2. Using ohmmeter, ensure continuity is present between relay terminals "STA" and "E1". (Scheme 47) Ensure no continuity is present between relay terminals "B" and "FC". Ensure no continuity is present between relay terminals "B" and "FP".
3. Attach battery voltage to terminal "STA" terminal and ground terminal "E1". Ensure continuity is present between terminals "B" and "FP". Apply battery voltage to terminal "B" and ground terminal "FC". Ensure continuity is present between terminals "B" and "FP". Replace relay if not as specified.

Scheme 47

ISC Motor

See IDLE CONTROL SYSTEM in this article.

FUEL DELIVERY

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

Fuel Pressure Regulator Vacuum Switching Valve (Prizm GSi)

Information not available from manufacturer.

Note. Following procedure applies if Code 24 is stored in ECM only (not transaxle Electronic Control Unit (ECU) on 4-speed applications) or when incorrect input from vehicle speed sensor is suspected.

Vehicle Speed Sensor ECM Code 24

Note. Following procedure applies to 4-speed A/T models with Code 24 stored in transaxle Electronic Control Unit (ECU) ONLY (not electronic control module) or when incorrect input from vehicle speed sensor is suspected.

1. Check speedometer operation. If speedometer operates correctly, proceed to step 2). Repair or replace speedometer if speedometer is not operating properly.
2. Disconnect 24-pin connector from ECM. Disconnect speedometer cable from speedometer head. On 4-speed models, disconnect 16-pin connector from ECU for the transaxle.
3. On all applications, using ohmmeter, check resistance from White wire of ECM connector to ground. Measure resistance while rotating speedometer cable.
4. If resistance varies between zero ohms and infinity, on M/T and 3-speed models, replace ECM. On 4-speed A/T models, go to step 9). On all applications, if reading was steady and less than one ohm, go to step 5). If reading was steady at infinite ohms, go to step 7).
5. Disconnect 10-pin connector C2 from instrument cluster. Connect ohmmeter between White and Black/Pink wire terminals of instrument cluster. Measure resistance while rotating speedometer.
6. If resistance varies between zero ohms and infinity, repair short to ground in White wire between instrument cluster and ECM on all models. On 4-speed A/T models, check for short to ground in White wire between instrument cluster and ECU. On all applications, if resistance did not fluctuate, replace vehicle speed sensor.
7. Backprobe White wire of 10-pin connector C2 at instrument cluster. Measure resistance between White wire and ground while rotating speedometer. If resistance varies between zero ohms and infinity, repair open in White wire between instrument cluster and ECM on all models. If resistance did not fluctuate, proceed to step 8.
8. Disconnect 10-pin connector C2 from instrument cluster. Measure resistance between Black/Pink wire and ground. If resistance is greater than .3 ohm, repair Black/Pink wire between instrument panel and battery. If reading is less than .3 ohm, replace vehicle speed sensor.
9. Raise and support vehicle under lower control arms. Install 24-pin connector on ECM. DO NOT install 16-pin connector on ECU. With engine idling, retest ECM for stored trouble codes after all trouble codes are cleared. If Code 24 is not present, replace ECU. If Code 24 is set again, replace ECM.

Cold Start Injector

Using an ohmmeter, ensure resistance across cold start injector terminals is 3-5 ohms. Replace cold start injector if not within specification.

Cold Start Switch

1. With engine temperature at less than 95°F (35°C), disconnect cold start switch Brown connector, located below distributor. Using an ohmmeter, ensure resistance across cold start switch terminals is 20-60 ohms.
2. Ensure resistance between Black/White wire on cold start switch and ground is 20 ohms or less. Replace cold start switch if resistance is not as specified.

Fuel Injector

Check resistance across injector terminals. See INJECTOR RESISTANCE SPECIFICATIONS table in this article. If resistance is not within specification, replace injector.

INJECTOR RESISTANCE SPECIFICATIONS

See ENGINE SENSORS & SWITCHES in this article.

Air Valve

With engine temperature at 140°F (60°C) or less, air valve should be open. With engine at normal operating temperature, valve should be closed. Replace valve if it does not perform as described.

Idle Speed Control Solenoid Valve (Prizm)

Information not available from manufacturer.

Idle-Up Vacuum Switching Valve (IVSV) (Prism GSi)

Information not available from manufacturer.

IGNITION SYSTEM

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

EGR System Check

1. With engine cool, grasp top of EGR valve and check for looseness. If looseness is felt, replace EGR valve. Warm engine to normal operating temperature. Place finger on bottom of EGR valve diaphragm. Start engine and increase engine speed. Note if EGR valve diaphragm moves. CAUTION: Wear gloves if EGR valve is hot.
2. If diaphragm does not move, allow engine to idle. Disconnect vacuum hose from EGR valve and apply 10 in. Hg of vacuum. Vacuum should hold and engine should run rough or should stall. If vacuum does not hold, go to step 4).
3. If engine did run rough or stall and EGR valve held vacuum, check components controlling vacuum supply to EGR valve, i.e. EGR modulator, EGR vacuum switching valve, vacuum supply and hoses. Also, check ECM control of ground circuit to EGR vacuum switching valve and verify EGR vacuum switching valve has power when ignition is on. For wire colors and ECM terminal identification, see appropriate wiring diagram in WIRING DIAGRAMS article.
4. If EGR valve did not hold vacuum, replace EGR valve. If engine did not run rough or stall, remove EGR valve and check for plugged EGR valve or EGR passages in intake/exhaust system. Clean or replace as necessary.

EGR Vacuum Supply

Locate EGR vacuum supply port on throttle body or intake manifold. Disconnect vacuum supply hose and connect hand-held vacuum gauge to port. Start engine and increase engine speed to 2000 RPM. Check vacuum gauge. Gauge reading should be greater than 20 in. Hg vacuum. If gauge reading is not at least 20 in. Hg vacuum, check vacuum supply port for restriction (carbon, dirt, etc.).

EGR Modulator

1. Remove vacuum hoses from modulator. Plug modulator ports No. 2 and No. 3. (Scheme 48) Connect hand-held vacuum pump to port No. 4 and apply vacuum. Vacuum should not hold. If vacuum holds, check for plugged modulator filter. If filter is not plugged, replace EGR modulator.
2. Connect vacuum hose to modulator port No. 5. Blow into hose. Again apply vacuum to port No. 4. Vacuum should now hold. If vacuum does not hold, replace EGR modulator.

Scheme 48

EGR Vacuum Switch Valve (VSV)

1. With ignition off, disconnect vacuum hoses and wiring from solenoid. For location of VSV, see EGR VACUUM SWITCHING VALVE LOCATIONS table. Using ohmmeter, ensure resistance between terminals of solenoid is 33-39 ohms.
2. Blow into tube No. 1 and ensure air flows through filter only. (Scheme 49) Apply battery voltage and ground to solenoid terminals. With solenoid energized, blow into port No. 1 to ensure air flows out port No. 2. Replace assembly if defective.
3. Check ECM control of ground circuit to EGR vacuum switching valve and verify EGR vacuum switching valve has power when ignition is on. For wire colors and ECM terminal identification, see appropriate wiring diagram in WIRING DIAGRAMS article.

EGR VACUUM SWITCHING VALVE LOCATIONS

Scheme 49

Charcoal Canister Check Valve

1. With canister removed, blow into tank port of canister. Ensure air flows from purge port and air inlet (bottom of canister). (Scheme 50)
2. Blow into purge port. Air should not flow from any ports. Replace canister and check valve if they do not perform as indicated.

Scheme 50

Fuel Evaporation Bimetallic Vacuum Switching Valve (BVSV)

1. Remove vacuum hoses from BVSV, located on intake manifold. With engine temperature less than 95°F (35°C), connect a hose to port side of BVSV. Blow into valve. No air should pass through valve.
2. With engine temperature greater than 122°F (50°C), blow into valve. Air should pass through valve. If BVSV does not perform as indicated, replace valve.

PCV Valve

Remove PCV valve from valve cover. Run engine at idle and place thumb over end of hose to check for vacuum. If vacuum is not present, check for plugged hoses or plugged manifold port. Turn engine off and remove PCV valve. Shake valve to ensure needle inside valve is free. Replace valve if it is not free.