Engine Controls - System/component Tests: Other Toyota Tercel L50

Power & Ground Circuits

For testing of power/ground circuits, see procedures in the PIN VOLTAGE CHART S article. See ECM LOCATION table for identifying ECM mounting locations.

ECM LOCATION

Note. Fig. (Scheme 11) identifies ECM terminals which are used for performing tests on various components in this article.

Scheme 11

CAMSHAFT POSITION SENSOR

For checking camshaft position sensor, see CAMSHAFT POSITION SENSOR under IGNITION CHECKS (DISTRIBUTORLESS IGNITION SYSTEM) in the BASIC TESTING article.

CRANKSHAFT POSITION SENSOR

For checking crankshaft position sensor, see CRANKSHAFT POSITION SENSOR under IGNITION CHECKS (DISTRIBUTORLESS IGNITION SYSTEM) in the BASIC TESTING article.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

1. Ensure ignition is off. Disconnect electrical connector from ECT sensor. See «ENGINE COOLANT TEMPERATURE (ECT) SENSOR LOCATION»(ref-21636-S36358110112001010300000) table. To verify wire colors for proper sensor identification, see wiring diagram in the WIRING DIAGRAMS article. NOTE: The ECT may be also identified using appropriate illustration in the «THEORY/OPERATION»(ref-21704) article.
2. Using ohmmeter, check resistance between ECT sensor electrical terminals. Resistance should be within specification at designated temperature. (Scheme 12) Replace ECT sensor if resistance is not within specification.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR LOCATION

Scheme 12

INTAKE AIR TEMPERATURE (IAT) SENSOR

1. Ensure ignition is off. Disconnect electrical connector from intake air temperature sensor. Intake air temperature sensor is located in air intake, near air filter. NOTE: Intake air temperature sensor may be also identified using appropriate illustration in the «THEORY/OPERATION»(ref-21704) article.
2. Remove intake air temperature sensor. Place threaded end of intake air temperature sensor and thermometer in container of water. Attach ohmmeter between intake air temperature sensor electrical terminals.
3. Heat water and note that resistance is within specification in relation to temperature. (Scheme 12) Replace intake air temperature sensor if defective.

KNOCK SENSOR

1. Knock sensor(s) are located on the cylinder block. (Scheme 13) Remove knock sensor from cylinder block before testing. See the REMOVE/INSTALL/OVERHAUL article.
2. Using ohmmeter, check that no continuity exists between electrical terminal of knock sensor and body of knock sensor. Replace knock sensor if continuity exists.

Scheme 13

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

1. Ensure ignition is off. To check MAP sensor supply voltage, disconnect electrical connector from MAP sensor. See «MAP SENSOR LOCATION»(ref-21636-S22038211192001010300000) table. NOTE: MAP sensor may also be identified using appropriate illustration in the «THEORY/OPERATION»(ref-21704) article. The MAP sensor has a vacuum hose connected to it and may be identified by wire colors. See wiring diagram in the WIRING DIAGRAMS article. MAP SENSOR LOCATION Application Location Tercel Passenger's Side Of Engine Compartment, On Firewall, Near Wiper Motor
2. Turn ignition on. Using voltmeter, measure voltage between terminals VC or VCC and E2 of electrical connector on wiring harness. (Scheme 14) The VC or VCC and E2 terminals are the 2 outer terminals on all models. Voltage should be within specification. See «MAP SENSOR SUPPLY VOLTAGE SPECIFICATIONS»(ref-21636-S32340835692001010300000) table. MAP SENSOR SUPPLY VOLTAGE SPECIFICATIONS Application Volts Tercel 4.50-5.50
3. If supply voltage is not within specification, check wiring circuit. See wiring diagram in the WIRING DIAGRAMS article. If supply voltage is correct, turn ignition off. Reinstall electrical connector on MAP sensor.
4. To check MAP sensor output voltage, turn ignition on. Disconnect MAP sensor vacuum hose from intake manifold. Connect voltmeter to terminals PIM and E2 of ECM. (Scheme 15) See the «ECM LOCATION»(ref-21636-S01253196582001010300000) table.
5. Measure and record output voltage under ambient atmospheric pressure. Attach vacuum pump to MAP sensor.
6. Apply vacuum in specified increments and measure MAP sensor output voltage drop at each increment. See «MAP SENSOR OUTPUT VOLTAGE DROP SPECIFICATIONS»(ref-21636-S24099183002001010300000) table. Replace MAP sensor if output voltage drop is not within specification.

MAP SENSOR OUTPUT VOLTAGE DROP SPECIFICATIONS

Scheme 14

Scheme 15

PARK/NEUTRAL POSITION (PNP) SWITCH CIRCUIT

If problem exists with park/neutral position switch or circuit, a diagnostic trouble Code P1780 will be stored in the Engine Control Module (ECM). See the TESTS W/CODES article for accessing diagnostic trouble codes.

A/T Models

1. Disconnect electrical connector from park/neutral position switch, mounted on side of transmission or transaxle. Note terminal identification. (Scheme 16)
2. Using ohmmeter, check for continuity at specified terminals with gearshift in proper positions. See the «PARK/NEUTRAL POSITION SWITCH SPECIFICATIONS»(ref-21636-S27009923372001010300000) table. If proper continuity cannot obtained, adjust switch. Replace switch if proper continuity cannot be obtained.

PARK/NEUTRAL POSITION SWITCH SPECIFICATIONS

Scheme 16

SUB-OXYGEN SENSOR

Note. Sub-oxygen sensor may be used only on varied applications on some models. See the OXYGEN SENSOR APPLICATION table.

Sub-oxygen sensor is mounted on exhaust pipe behind catalytic converter. Sub-oxygen sensor may be referred to as an oxygen sensor. If sub-oxygen sensor or circuit fails, a diagnostic trouble Code PO141 will set in Engine Control Module (ECM) memory. For diagnosis of sub-oxygen sensor and circuit, see Code PO141 in the TROUBLE CODE CHART in the TESTS W/CODES article.

OXYGEN SENSOR HEATER

1. Disconnect electrical connector from oxygen sensor and note oxygen sensor terminals. (Scheme 17)
2. Using ohmmeter, measure resistance between oxygen sensor terminals +B and HT. (Scheme 17) Replace oxygen sensor if resistance is not within specification. See the «OXYGEN SENSOR HEATER RESISTANCE SPECIFICATIONS»(ref-21636-S36974549602001010300000) table.

OXYGEN SENSOR HEATER RESISTANCE SPECIFICATIONS

Scheme 17

SUB-OXYGEN SENSOR HEATER

1. Electrical connector for sub-oxygen is located on passenger's side of console, just below shift lever, beneath the carpet. Disconnect electrical connector from sub-oxygen sensor and note sub-oxygen sensor terminals. (Scheme 18)
2. Using ohmmeter, measure resistance between sub-oxygen sensor terminals +B and HT. (Scheme 18) Replace sub-oxygen sensor if resistance is not 11-16 ohms at 68°F (20°C).

Scheme 18

PICK-UP COILS

See PICK-UP COIL AIR GAP and PICK-UP COIL RESISTANCE under IGNITION CHECKS (DISTRIBUTOR TYPE IGNITION SYSTEM) in the BASIC TESTING article.

THROTTLE POSITION SENSOR

1. Turn ignition off. Disconnect electrical connector from Throttle Position Sensor (TPS) on throttle body. Note terminal identification. (Scheme 19) NOTE: Some models require that vacuum be applied to throttle opener before checking TPS. See «TPS RESISTANCE SPECIFICATIONS»(ref-21636-S04416518712001010300000) table. NOTE: On A/T models, disconnect throttle cable from linkage before checking TPS.
2. Insert specified thickness feeler gauge between throttle stop screw and throttle lever and check resistance or continuity. See the «TPS RESISTANCE SPECIFICATIONS»(ref-21636-S04416518712001010300000) table. Replace or adjust TPS if not within specification.

Scheme 19

TPS RESISTANCE SPECIFICATIONS (1)

VEHICLE SPEED SENSOR

1. Vehicle speed sensor is located on rear of combination meter in instrument cluster. Connect ohmmeter between terminals "A" and "B". Terminals are located near vehicle speed sensor. (Scheme 20)or (Scheme 21).
2. Rotate speedometer cable shaft and note reading. Ohmmeter should deflect from continuity to no continuity 4 times per speedometer cable shaft revolution. Replace speedometer if reading does not deflect as specified.

Scheme 20

Scheme 21

FUEL PUMP ELECTRONIC CONTROL UNIT

See FUEL DELIVERY under FUEL SYSTEM.

CIRCUIT OPENING RELAY

1. Ensure ignition is off. Remove circuit opening relay. See «CIRCUIT OPENING RELAY LOCATION»(ref-21636-S18891039782001010300000) table. NOTE: Circuit opening relay may also be identified using appropriate illustration in the «THEORY/OPERATION»(ref-21704) article or wire color. See wiring diagram in the WIRING DIAGRAMS article. CIRCUIT OPENING RELAY LOCATION Application Relay Location Tercel Below Dash, Near Driver's Side Of Steering Column
2. Using ohmmeter, check continuity between specified terminals. (Scheme 22)
3. Check circuit opening relay operation by applying battery voltage and ground and checking continuity between specified terminals. (Scheme 23) Replace circuit opening relay if defective.

Scheme 22

Scheme 23

EFI MAIN RELAY

1. Ensure ignition is off. Remove EFI main relay. See «EFI MAIN RELAY LOCATION»(ref-21636-S16064676872001010300000) table. NOTE: The EFI main relay may also be identified using appropriate illustration in the «THEORY/OPERATION»(ref-21704) article or wire color. See wiring diagram in the WIRING DIAGRAMS article. EFI MAIN RELAY LOCATION Application Location Tercel Fuse/Relay Box Near Driver's Side Front Corner Of Engine Compartment
2. Using ohmmeter, check continuity between specified terminals. (Scheme 24)
3. Check EFI main relay operation by applying battery voltage and ground and checking continuity between specified terminals. (Scheme 25) Replace EFI main relay if defective.

Scheme 24

Scheme 25

See CIRCUIT OPENING RELAY under RELAYS.

See EFI MAIN RELAY under RELAYS.

Fuel Pump Pressure

For fuel pump pressure testing, see FUEL PRESSURE in the BASIC TESTING article.

Fuel Injectors

1. Ensure ignition is off. Disconnect electrical connector at fuel injector. Using ohmmeter, measure resistance between fuel injector electrical terminals. Replace fuel injector if resistance is not within specification. See «FUEL INJECTOR RESISTANCE SPECIFICATIONS»(ref-21636-S09117491862001010300000) table.
2. To check fuel injector spray pattern and volume, remove fuel injector. See the REMOVE/INSTALL/OVERHAUL article. Disconnect fuel hose from fuel filter outlet. Use Delivery Hose (09268-41045) to install fuel injector between fuel filter and fuel pressure regulator. (Scheme 26)and (Scheme 27).
3. Place fuel injector into a clean graduated container. Place vinyl tube on end of fuel injector to prevent fuel spillage. NOTE: Scan tester is used to operate the fuel pump or by applying battery voltage to electric fuel pump.
4. Use scan tester to operate the fuel pump or apply battery voltage to electric fuel pump to pressurize the fuel system. See FUEL PRESSURE in the «BASIC TESTING»(ref-21589) article.
5. Connect fuel injector tester to fuel injector for 15 seconds. Use Fuel Injector Tester (09842-30070).
6. Measure fuel injector volume and check spray pattern. Test each fuel injector 2-3 times. Replace fuel injector if volume is not as specified. See the «FUEL INJECTOR VOLUME SPECIFICATIONS»(ref-21636-S10732947912001010300000) table. NOTE: Ensure difference between fuel injector volume on all fuel injectors is within specification. See FUEL INJECTOR VOLUME SPECIFICATIONS table.
7. Disconnect fuel injector tester. Ensure fuel leakage from end of fuel injector is one drop or less in specified time. See the «FUEL INJECTOR LEAKAGE SPECIFICATIONS»(ref-21636-S36089750572001010300000) table. Replace fuel injector if leakage exceeds specified amount.

FUEL INJECTOR RESISTANCE SPECIFICATIONS

FUEL INJECTOR VOLUME SPECIFICATIONS

FUEL INJECTOR LEAKAGE SPECIFICATIONS

Scheme 26

Scheme 27

Fuel Cut System

1. When checking fuel cut system, engine RPM must be monitored.
2. Scan tester is connected to data link connector No. 3 for monitoring engine RPM. For connecting of scan tester, see appropriate application under IDLE SPEED & MIXTURE in the «ADJUSTMENTS»(ref-21635) article. CAUTION: Some tachometers may not be compatible with ignition system. Consult tachometer manufacturer before connecting tachometer to system. To avoid possible damage to ignitor and/or coil, DO NOT allow tachometer terminal to become grounded.
3. Start and warm engine to normal operating temperature. Ensure all accessories are off. Gradually increase engine RPM to maintain at least specified engine speed. See «FUEL CUT SYSTEM TESTING SPECIFICATION»(ref-21636-S26362587142001010300000) table. FUEL CUT SYSTEM TESTING SPECIFICATION Application Engine RPM Tercel 2500
4. Using stethoscope, check for fuel injector operating sound. Ensure when throttle lever is released, fuel injector stops operating momentarily (fuel cut RPM) and then resumes operating (fuel return RPM).
5. Ensure fuel cut RPM (if available) and fuel return RPM are within specification. See «FUEL CUT SYSTEM SPECIFICATIONS»(ref-21636-S37369639242001010300000) table. Shut engine off. Remove test equipment.

FUEL CUT SYSTEM SPECIFICATIONS (1)

IDLE AIR CONTROL (IAC) VALVE

1. Warm engine to normal operating temperature. Ensure idle speed is correct. See IDLE SPEED & MIXTURE in the «ADJUSTMENTS»(ref-21635) article.
2. Apply parking brake and place transmission/transaxle in Neutral. Install Jumper Wire (SST 09843-18020) between terminals TE1 and E1 of data link connector No. 1. (Scheme 28) Start engine and note RPM. NOTE: Data link connector No. 1 is located in engine compartment.
3. Engine RPM should increase to specified RPM for 5 seconds, and then return to idle. See «IAC VALVE ENGINE SPEED TESTING SPECIFICATIONS»(ref-21636-S18156217062001010300000) table. IAC VALVE ENGINE SPEED TESTING SPECIFICATIONS Application Engine RPM Tercel 900-1300
4. If engine RPM is not as specified, check IAC valve resistance and operation. If engine RPM is within specification, remove jumper wire. Turn ignition off.
5. To check IAC valve resistance, ensure ignition is off. Disconnect electrical connector from IAC valve located on lower area of throttle body. Using ohmmeter, measure resistance between terminal B+ or +B and each remaining terminal. (Scheme 29)
6. Replace IAC valve if resistance is not within specification. See «IAC VALVE RESISTANCE SPECIFICATIONS»(ref-21636-S17683514042001010300000) table.
7. To check IAC valve operation, remove IAC valve from throttle body. Connect battery voltage and ground to proper terminals and ensure valve opens and closes. (Scheme 30) Replace IAC valve if defective.
8. If IAC valve resistance is correct and operates correctly, check wiring circuit between Engine Control Module (ECM) and IAC valve. See ECM LOCATION table. See wiring diagram in the WIRING DIAGRAMS article.

IAC VALVE RESISTANCE SPECIFICATIONS

Scheme 28

Scheme 29

Scheme 30

IGNITION SYSTEM

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

See KNOCK SENSOR under ENGINE SENSORS & SWITCHES.

EGR VACUUM MODULATOR

Note. When testing EGR vacuum modulator, it will be necessary to monitor engine RPM by using tachometer or scan tester depending on model application. For tachometer or scan tester connections, see IDLE SPEED & MIXTURE in the ADJUSTMENTS article.

1. Mark vacuum hose locations and disconnect vacuum hoses from EGR vacuum modulator. Block ports "P" and "R" on EGR vacuum modulator. see scheme 22 NOTE: Ports "P" and "R" are the double ports on side of EGR vacuum modulator. Port "Q" is single port on side of EGR vacuum modulator.
2. Apply air pressure to port "Q". see scheme 22 Air should pass freely through air filter side of EGR vacuum modulator.
3. Start and operate engine at specified RPM. See «EGR VACUUM MODULATOR TESTING SPECIFICATIONS»(ref-21636-S02272600952001010300000) table. Repeat test procedures in steps 1) and 2). Strong resistance of airflow should be felt. Replace EGR vacuum modulator if resistance is not felt. Reconnect vacuum hoses to proper locations.

EGR VACUUM MODULATOR TESTING SPECIFICATIONS

EGR VACUUM SWITCHING VALVE (VSV)

Note. When testing EGR VSV, use proper illustration to determine component location. see scheme 23

1. Disconnect electrical connector from EGR VSV. Using ohmmeter, check resistance between EGR VSV electrical terminals.
2. Replace EGR VSV if resistance is not within specification. See «EGR VSV RESISTANCE SPECIFICATIONS»(ref-21636-S03686785412001010300000) table. Check that no continuity exists between each electrical terminal and EGR VSV body. Replace EGR VSV if continuity exists between any electrical terminal and VSV body.
3. Apply air pressure to port "E" without battery connected. (Scheme 31) Air pressure should not flow through port "F". Connect battery voltage and ground to EGR VSV electrical terminals. (Scheme 31) Apply air pressure to port "E". Air pressure should flow from port "F". Replace EGR VSV if defective.

EGR VSV RESISTANCE SPECIFICATIONS

Scheme 31

FUEL EVAPORATION SYSTEM

Note. Fuel evaporation systems contain different components depending on application. see scheme 23 When testing fuel evaporation system components, use proper illustration to determine component location.

EVAP Thermal Vacuum Valve

1. Drain cooling system. Remove EVAP TVV located in coolant passage. see scheme 23
2. Use cool water to cool threaded end of EVAP TVV to less than 122°F (50°C). Apply air pressure to top port on EVAP TVV. Ensure EVAP TVV is closed and no air will pass through lower port.
3. Heat water to greater than 149°F (65°C). Apply air pressure to top port on EVAP TVV. Ensure EVAP TVV is open and air passes through lower port. Replace EVAP TVV if defective. Apply thread sealant to threads of EVAP TVV and reinstall. Fill cooling system.

Charcoal Canister

1. Disconnect hoses from charcoal canister. Check for clogged filter and/or stuck check valve by applying low air pressure to port "A". (Scheme 32) Ensure air flows freely from other ports on charcoal canister.
2. Apply low air pressure to port "B". (Scheme 32) Ensure no air flows from any other ports on charcoal canister. Replace charcoal canister if defective.
3. To clean charcoal canister filter, apply 43 psi (3 kg/cm 2 ) air pressure to port "A" while holding port "B" closed. Ensure no activated carbon comes out of charcoal canister. DO NOT attempt to wash out charcoal canister.

Scheme 32

POSITIVE CRANKCASE VENTILATION (PCV)

1. Remove PCV valve. Attach hose to PCV valve. Blow air from cylinder head side of PCV valve. Ensure air passes easily through PCV valve.
2. Blow air from intake manifold side of PCV valve. Ensure air passes through PCV valve with some restriction. Replace PCV valve if valve does not function as described.