Engine Controls - System/component Tests Lexus LS I

INTRODUCTION

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

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.

CONTROL UNIT

ES250 POWER CIRCUITS

1. Ensure ignition is off. Disconnect connectors from ECU. Remove locks so ECU connector can be easily backprobed. (Scheme 9) Reconnect ECU connectors.
2. Turn ignition on. Using a DVOM, measure voltage between ground and ECU terminals BATT, B1 and E1. (Scheme 10) Battery voltage should be present.
3. If battery voltage is not present, check 40-amp MAIN fuse and 15-amp EFI fuse. Also ensure wire harness is not open or shorted. If fuses and wire harness are okay and conditions indicate ECU may be faulty, substitute a known good ECU. If condition improves, replace original ECU.

Scheme 9

Scheme 10

ES250 GROUND CIRCUITS

1. Ensure ignition is off. Disconnect connectors from ECU. Remove locks so ECU connectors can be easily backprobed. (Scheme 9) Reconnect ECU connectors.
2. Using an ohmmeter, check for continuity to ground on ECU terminals E1, E01 and E02. (Scheme 10) Resistance should be zero ohms. If resistance is not zero ohms, repair open to ground.
3. 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 greater than one volt, check for open, corrosion and loose connection on ground lead.

Note. For testing LS400 power circuit, refer to ECU POWER SOURCE CIRCUIT, BACK-UP POWER SOURCE CIRCUIT and TERMINAL TE1 & TE2 CIRCUIT diagnosis charts at end of article. See CIRCUIT DIAGNOSIS CHARTS .

LS400 GROUND CIRCUITS

1. Ensure ignition is off. Using a DVOM, measure resistance between ECU terminal No. 22 of connector E10 and ground with ECU connector connected. (Scheme 11)
2. Resistance should be one ohm or less. If resistance is within specification, no fault is present with ground circuits. If resistance is not within specification, carefully disconnect ECU connector.
3. Check ECU ground terminal and wire harness connector for corrosion and damage. Repair as necessary.

Scheme 11

AIRFLOW METER AIR TEMPERATURE SENSOR RESISTANCE

Turn ignition off. Disconnect the airflow meter connector. Using a DVOM, measure resistance between the airflow meter terminals as shown. (Scheme 12)& 5. For resistance specifications, refer to the AIRFLOW METER AIR TEMPERATURE SENSOR RESISTANCE table.

Scheme 12

Scheme 13

AIRFLOW METER AIR TEMPERATURE SENSOR RESISTANCE

ES250 AIRFLOW METER MEASURING PLATE RESISTANCE

Using a DVOM, measure resistance between airflow meter terminals while moving airflow measuring plate inside the airflow meter. (Scheme 12)& 5. For resistance specifications, refer to the AIRFLOW METER MEASURING PLATE RESISTANCE table.

AIRFLOW METER MEASURING PLATE RESISTANCE

ES250 CLUTCH START SWITCH

1. Ensure clutch pedal height is correct. Pedal height is measured from floorboard (carpet removed) to face of pedal. Pedal height should be 7.52-7.91" (191-201 mm).
2. Clutch pedal free play should be .20-.59" (5.1-15 mm). Push rod play at top of clutch pedal should be .039-.197" (1-5 mm). Adjust pedal height, pedal free play and push rod play as necessary.
3. Disconnect clutch switch connector. Using an ohmmeter, check for continuity across switch terminals when clutch pedal switch is depressed. Continuity should not exist when clutch pedal is released. If continuity is not as specified, replace clutch switch.

NEUTRAL START SWITCH

Note. For more LS400 information, refer to NEUTRAL START SWITCH CIRCUIT diagnosis chart at end of article.

Neutral start switch is located on side of transaxle. Turn ignition off. Disconnect neutral start switch connector. Using a DVOM, check for continuity between terminals specified in the appropriate NEUTRAL START SWITCH CONTINUITY table below. (Scheme 14)& 7. If continuity is not as specified, replace neutral start switch.

ES250 NEUTRAL START SWITCH CONTINUITY

LS400 NEUTRAL START SWITCH CONTINUITY

Scheme 14

Scheme 15

THROTTLE POSITION SENSOR (TPS)

Turn ignition off. Disconnect TPS connector. Using a DVOM, measure resistance between specified TPS terminals in appropriate TPS SPECIFICATIONS table below. (Scheme 16)

ES250 TPS SPECIFICATIONS

LS400 TPS SPECIFICATIONS

Scheme 16

CIRCUIT OPENING RELAY

Note. For more LS400 information, see FUEL SYSTEM CIRCUIT diagnosis chart at end of article. See CIRCUIT DIAGNOSIS CHARTS .

1. Turn ignition off. Circuit opening relay is located under engine ECU on ES250 and on right side of engine ECU on LS400. Remove relay from vehicle. Using an ohmmeter, check for continuity between relay terminals STA and E1 on ES250 or ST and E1 on LS400. (Scheme 17)& 10. Check for continuity between terminals B and FC on ES250 or IG and FC on LS400. Ensure continuity does not exist between terminals B and FP. If continuity is not as specified, replace relay.
2. Apply battery voltage between terminals STA and E1 on ES250 or ST and E1 on LS400. Using an ohmmeter, ensure continuity is present between terminals B and FP. Apply battery voltage between terminals B and FC on ES250 or IG and FC on LS400. Ensure continuity is present between terminals B and FP. If continuity is not as specified, replace relay.

Scheme 17

Scheme 18

EFI MAIN RELAY

Note. For more LS400 information, see ECU POWER SOURCE CIRCUIT diagnosis chart at end of article. Refer to CIRCUIT DIAGNOSIS CHARTS .

1. EFI main relay is located in junction block No. 2. (Scheme 28)or (Scheme 29). Using an ohmmeter, check for continuity between relay terminals No. 1 and 3. (Scheme 31)-32. Ensure continuity is not present between terminals No. 2 and 4. If continuity is not as specified, replace relay.
2. Apply battery voltage between relay terminals No. 1 and 3. Using an ohmmeter, check for continuity between terminals No. 2 and 4. If continuity is not as specified, replace relay.

STARTER RELAY

1. ES250 starter relay is located in relay block No. 1 in driver-side kick panel area. LS400 starter relay is located in junction block No. 2 in left side of engine compartment. Remove starter relay. Using an ohmmeter, check for continuity between starter relay terminals No. 1 and 3. (Scheme 19)
2. Ensure no continuity is present between relay terminals No. 2 and 4. If continuity is not as specified, replace relay.
3. Apply battery voltage between relay terminals No. 1 and 3. Using an ohmmeter, check for continuity between relay terminals No. 2 and 4. If continuity is not present, replace relay.

Scheme 19

FUEL CONTROL SYSTEM

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

Note. For more LS400 information, refer to FUEL SYSTEM CIRCUIT, INJECTOR CIRCUIT, COLD START INJECTOR CIRCUIT and FUEL PRESSURE CONTROL VACUUM SWITCHING VALVE (VSV) CIRCUIT diagnosis charts at end of article. See CIRCUIT DIAGNOSIS CHARTS .

FUEL CUT SYSTEM

1. Start and warm engine to operating temperature. Ensure A/C is off. Connect a tachometer to engine. Disconnect Throttle Position Sensor (TPS) connector. Using a jumper wire, connect terminals IDL and E2 of harness connector. (Scheme 23)
2. Gradually increase engine speed. Observe tachometer as engine RPM is raised. RPM will fluctuate between fuel cut and fuel return points. See «FUEL CUT RPM SPECIFICATIONS»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.
3. If fuel cut system does not function properly, ensure a clearance of.028" (.71 mm) is present between screw and lever on TPS. Ensure wiring harness is okay between TPS connector and ECU connector.

FUEL CUT RPM SPECIFICATIONS

Scheme 20

Scheme 21

1. Start engine. Using a stethoscope, ensure each injector is making a "clicking" noise during operation. If "clicking" noise is not heard, ensure wiring connector is securely fastened.
2. Ensure an injector signal is present on injector harness connector. Turn engine off. Disconnect injector electrical connector. Using a DVOM, measure resistance across injector terminals.
3. Resistance should be approximately 13.8 ohms. If resistance is not as specified, replace fuel injector. Disconnect negative battery cable. Remove injector from engine.
4. Place injector into a container to catch fuel spray. Turn ignition on. DO NOT start engine. Using a jumper wire, connect terminals FP and +B of check connector. (Scheme 21)
5. Connect battery voltage to injector terminals for 15 seconds. Ensure an even cone shaped fuel spray is observed from injector. If fuel spray is not satisfactory, replace injector. If fuel spray is satisfactory, check volume of fuel delivered by fuel injector.
6. On ES250, fuel volume should be 2.7-3.4 Cu. In. (45-55 cc) for 15 seconds of operation. On LS400, fuel volume should be 3.4-4.3 Cu. In. (55-70 cc) for 15 seconds of operation. Check each injector 2-3 times for volume. Maximum volume difference between injectors is.3 Cu. In. (5 cc) for ES250 or.6 Cu. In. (10 cc) for LS400. If volume is not satisfactory, replace injector.
7. Remove battery voltage from injector. With injector still placed in container, observe injector tip. On ES250, if injector drips more than one drop of fuel within one minute, replace fuel injector. On LS400, no more than 1 drop in 3 minutes is acceptable.

FUEL PRESSURE CONTROL SYSTEM

1. Ensure water temperature sensor is functioning properly before diagnosing fuel pressure control system. See CODE 22 in G - TEST W/ CODES article in this section. Ensure airflow meter is functioning properly before diagnosing fuel pressure control system. See appropriate «AIRFLOW METER»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__airflow-meter-air-temperature-sensor-resistance) section in ENGINE SENSORS & SWITCHES.
2. Disconnect electrical connector from fuel pressure Vacuum Switching Valve (VSV). Using a DVOM, measure resistance between VSV terminals. Resistance should be 33-39 ohms (cold) on ES250 or 30-50 ohms on LS400. If resistance is not within specification, replace VSV.
3. Using a DVOM, check for continuity between each VSV terminal and ground (outside of VSV). If continuity is present, replace VSV. With electrical connector disconnected, ensure air flows between VSV ports.
4. Apply battery voltage between VSV terminals. Apply air to port E. (Scheme 22) Air should flow from port E to filter. If air does not flow as indicated, replace VSV.

Scheme 22

Scheme 23

1. Turn ignition off. Disconnect cold start injector electrical connector. (Scheme 23) Using a DVOM, measure resistance between cold start injector terminals. Resistance should be 2-4 ohms.If resistance is not as specified, replace cold start injector.
2. Disconnect negative battery cable. Remove cold start injector from engine. Place cold start injector into a container to catch fuel spray. Turn ignition on. DO NOT start engine.
3. Using a jumper wire, connect terminals FP and +B of check connector. (Scheme 21) Connect battery voltage to cold start injector terminals. CAUTION: Apply battery voltage to cold start injector and observe fuel spray as quickly as possible.
4. Ensure an even cone shaped fuel spray is observed from cold start injector. If fuel spray is not satisfactory, replace cold start injector. If fuel spray is satisfactory, remove battery voltage from cold start injector.
5. With cold start injector still placed in container, observe cold start injector tip. If injector drips more than one drop of fuel within one minute, replace cold start injector.
6. Using a DVOM, measure resistance of cold start injector time switch. See «COLD START INJECTOR TIME SWITCH RESISTANCE»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. (Scheme 24) If resistance is not as specified, replace cold start injector time switch.

COLD START INJECTOR TIME SWITCH RESISTANCE

Scheme 24

Scheme 25

1. Start engine. Idle engine for approximately 2 minutes. Turn engine off. Ensure a "clicking" sound is heard from ISC immediately after stopping engine.
2. Disconnect ISC valve connector. Using a DVOM, check resistance between terminals specified in «ISC VALVE RESISTANCE»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. (Scheme 25) If resistance is not as specified, replace ISC valve. ISC VALVE RESISTANCE Terminals Ohms B1 & S1 Or S3 10-30 B2 & S2 Or S4 10-30 NOTE: Wait approximately 20 seconds or longer before disconnecting negative battery cable after ignition is turned off.
3. Disconnect negative battery cable. Drain engine coolant. Disconnect ISC valve connector. Disconnect air hose and 2 water by-pass hoses from ISC valve.
4. Apply battery voltage between ISC valve terminals B1 and B2. Repeatedly ground ISC valve terminals S1, S2, S3 and S4 in sequence. (Scheme 25) Ensure ISC valve moves toward closed position.
5. With battery voltage applied to ISC valve, repeatedly ground ISC valve terminals S4, S3, S2 and S1 in sequence. (Scheme 25) Ensure ISC valve moves toward open position. If operation is not as outlined, replace ISC valve.

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

IGNITION COILS SYSTEM

Turn ignition off. Disconnect wires from ignition coil. (Scheme 26) Using an ohmmeter, check primary coil resistance on ignition coil. For resistance specifications, see IGNITION COIL RESISTANCE table.

IGNITION COIL RESISTANCE

Scheme 26

ADVANCE COMPONENTS

Ignition timing and advance are electronically controlled by engine ECU based on inputs from throttle position sensor, crank and cam angle sensors (or pick-ups), engine RPM sensor, etc.

An ignitor sends an ignition signal (controlled by ECU) to coil, interrupting primary current and generating ignition spark at correct time as calculated by ECU.

Scheme 27

1. Remove filters from EGR vacuum modulator. (Scheme 27) Using compressed air, clean filters. Install filters with coarse side facing outward.
2. Using a vacuum "T", connect a vacuum gauge between EGR vacuum hose and EGR valve (between EGR vacuum hose and vacuum switching valve on LS400). To ensure EGR valve is seating, start engine and check idle quality. If EGR valve is not seating, replace EGR valve.
3. With coolant temperature less than 104°F (40°C) on ES250 or 127°F (53°C) on LS400, vacuum gauge should indicate zero vacuum at 2500 RPM. Warm engine to operating temperature. Raise engine speed to 2500 RPM. Vacuum gauge should indicate approximately 2.76 in. Hg.
4. Disconnect vacuum hose from port "R" of EGR vacuum modulator (lower of two ports on side of modulator). (Scheme 27) Connect port "R" directly to intake manifold using another vacuum hose. Vacuum gauge should indicate high vacuum with engine at 3500 RPM on ES250 or 2500 RPM on LS400.
5. Engine may misfire slightly. Let engine idle. Remove vacuum gauge, and reconnect all vacuum hoses. Disconnect vacuum hose from EGR valve. Apply vacuum directly to EGR valve. Engine should run rough or stall. If results are as indicated, system is okay.

VACUUM MODULATOR CHECK

1. Turn engine off. Label and disconnect all vacuum hoses from EGR vacuum modulator. Block ports "P" and "R" with finger (twin ports on side of modulator). (Scheme 27) Blow air into port "Q" (single port on side of modulator). Air should flow freely out of filter.
2. Start engine, and run it at 3500 RPM on ES250 or 2500 RPM on LS400. Block ports "P" and "R" with finger. Blow air into port "Q". Air should not flow out of filter. If air flows out of filter, replace EGR vacuum modulator.

ES250 BIMETALLIC VACUUM SWITCHING VALVE

1. Turn engine off. Drain coolant from radiator. Remove bimetallic vacuum switching valve (BVSV). (Scheme 27) With BVSV less than 104°F (40°C), blow air into top port. Air should not pass through BVSV.
2. Heat BVSV to 129°F (54°C). Blow air into top port. Air should pass through BVSV. If BVSV does not operate as outlined, replace BVSV.

LS400 VACUUM SWITCHING VALVE

1. Turn engine off. Disconnect vacuum switching valve (VSV) electrical connector. VSV is located in-line between EGR valve and EGR vacuum modulator. Using ohmmeter, check VSV resistance. Resistance should be 33-39 ohms (cold).
2. Ensure continuity does not exist between each electrical terminal and VSV body. If continuity is present or resistance measurement in step 1) is incorrect, replace EGR VSV.
3. Identify and disconnect all vacuum hoses from (VSV). Blow air into upper port (near VSV filter). Air should flow freely out of lower port (near VSV electrical connector).
4. Apply battery voltage and ground to VSV electrical connector. Blow air into upper port. Air should flow out of filter. If air does not flow out of filter, replace EGR VSV.

EVAP CANISTER

1. Visually inspect EVAP canister and hoses for cracks and damage. Disconnect hoses from canister, and blow into canister port from fuel tank. Air should flow from other ports. Blow air into canister purge port. Air should not flow from other ports.
2. Clean canister filter by blowing a maximum of 43 psi (3 kg/cm 2 ) of compressed air through fuel tank port while blocking purge port outlet. No charcoal should come out. DO NOT attempt to wash canister.

BIMETALLIC VACUUM SWITCHING VALVE

1. Drain coolant, and remove bimetallic vacuum switching valve (BVSV). BVSV is located on coolant outlet. Cool BVSV to less than 95°F (35° C). Blow air into upper BVSV vacuum port. Air should not flow through BVSV ports on ES250. On LS400, air should flow from upper BVSV vacuum port through BVSV air filter (located on top of BVSV).
2. Heat BVSV in water to greater than 130°F (55°C). Blow air into upper BVSV vacuum port. On all models, air should flow from upper BVSV vacuum port through lower BVSV vacuum port.

EVAP VACUUM CONTROL VALVE (LS400)

1. Mark vacuum control valve (VCV) vacuum lines for reassembly. Remove VCV from vehicle. VCV is located in-line between BVSV and EVAP canister. Using a vacuum pump, apply 2.76 in. Hg to top vacuum port of VCV. Blow into one of 2 lower vacuum ports. Air should pass freely between lower vacuum ports.
2. Release vacuum from top vacuum port of VCV. Blow into one of 2 lower vacuum ports. Air should not pass between lower vacuum ports. If results are other than indicated, replace VCV.

PCV VALVE

1. Remove PCV valve from cylinder head cover. Attach a clean hose to cylinder head side of PCV valve. Blow into attached hose. Air should pass freely through PCV valve.
2. Reverse PCV valve, and place clean hose over intake manifold side of PCV valve. Blow air into attached hose. Air should not pass easily through PCV valve. If either condition is not met, replace PCV valve.
3. Inspect all PCV hoses, connections and gaskets for leaks and damage. Repair or replace as necessary.

DASHPOT

1. Start engine, and warm it to operating temperature. Ensure idle speed is correct. Remove cap, filter and separator from dashpot. Increase engine speed, and hold at 2500 RPM.
2. Plug small hole in back of dashpot using finger. Release throttle. When throttle is released, engine speed with cooling fan off should be 2000 RPM on ES250 or 1500 RPM for LS400.
3. If necessary, adjust dashpot. When installing separator, filter and cap, install filter with coarse side facing outside.
4. Increase engine speed, and hold at 2500 RPM. Release throttle. After a few seconds, engine should return to idle. If dashpot still does not function properly, replace dashpot.

A/C CLUTCH CONTROL

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

Note. For more LS400 information, refer to A/C COMPRESSOR CIRCUIT diagnostic chart at end of article.

A/C CLUTCH RELAY CONTROL

1. A/C clutch relay is located in junction block No. 2. (Scheme 28)or (Scheme 29).
2. Use an ohmmeter to check for continuity between relay terminals No. 1 and 3. (Scheme 31)-32. Ensure no continuity exists between relay terminals No. 2 and 4. If continuity is not as specified, replace relay.
3. Apply battery voltage between relay terminals No. 1 and 3. Using an ohmmeter, check for continuity between relay terminals No. 2 and 4 on ES250 or terminals No. 1 and 2 on LS400. If continuity is not present, replace relay.

Scheme 28

Scheme 29

1. Coolant temperature should be less than 185°F (85°C) on ES250 or less than 181°F (83°C) on LS400. Turn ignition on. Cooling fans should not rotate. If cooling fans rotate, check cooling fan relays and water temperature sensor (ES250) or water temperature switch (LS400). Check for damaged connectors and an open circuit between cooling fan relay and water temperature sensor/switch.
2. Disconnect water temperature sensor/switch connector. (Scheme 28)or (Scheme 29). With ignition on, cooling fans should operate. If cooling fans do not operate, check engine main relay and fuse. Check cooling fan motors. Also check cooling fan relays and water temperature sensor/switch. Check for damaged connectors or an open circuit between cooling fan relay and water temperature sensor/switch. If okay, go to step 3) for ES250 or step 4) for LS400.
3. On ES250, reconnect water temperature sensor. Start engine. Warm engine to operating temperature. Cooling fans should operate at low speed. If cooling fans do not operate at low speed, replace water temperature sensor.
4. On all models, reconnect water temperature sensor/switch. Warm engine to more than 199°F (93°C). Cooling fans should operate at high speed. If cooling fans do not operate at high speed, replace water temperature sensor/switch.
5. On LS400, cooling fan should also activate when A/C pressure switch indicates high A/C line pressure. Refer to «LS400 A/C PRESSURE SWITCH»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__ls400-ac-pressure-switch) under COOLING FAN CONTROL SYSTEM.

LS400 A/C PRESSURE SWITCH

1. Install A/C pressure gauge set. To access pressure switch, remove right headlight. Pressure switch is in-line with A/C receiver. Turn A/C selector switch to OFF position. High side pressure should be 142 psi (10 kg/cm 2 ) or less.
2. Disconnect switch terminal connector. Using a DVOM, check for continuity between switch terminals No. 2 (ohmmeter positive lead) and No. 3 (ohmmeter negative lead). (Scheme 31)-32.
3. Turn A/C selector switch to ON position. High side pressure should be 192 psi (13.5 kg/cm 2 ) or more. No continuity should exist between switch terminals No. 2 and No. 3. If A/C pressure switch continuity is not correct, replace switch.

ES250 COOLING FAN ECU

Turn ignition off. Disconnect cooling fan ECU. (Scheme 28) Using a DVOM, measure resistance and voltage as indicated in the COOLING FAN ECU SPECIFICATIONS table. Make all measurements from harness side of connector. (Scheme 30) Repair harness as necessary.

COOLING FAN ECU SPECIFICATIONS

Scheme 30

ES250 WATER TEMPERATURE SENSOR

Using a DVOM, measure resistance between water temperature sensor terminals. For water temperature sensor location (Scheme 28) See WATER TEMPERATURE SENSOR RESISTANCE table. If water temperature sensor is not within specification, replace sensor.

WATER TEMPERATURE SENSOR RESISTANCE

LS400 WATER TEMPERATURE SWITCH

Using a DVOM, check for continuity between water temperature switch terminals. For water temperature switch location (Scheme 29) See WATER TEMPERATURE SWITCH CONTINUITY table. If water temperature switch continuity is not as shown, replace switch.

WATER TEMPERATURE SWITCH CONTINUITY

Scheme 31

Scheme 32

Scheme 33

Scheme 34

Scheme 35

Scheme 36

ES250 & LS400 ENGINE MAIN & LS400 COOLING FAN RELAY NO. 3

1. Disconnect engine main relay. (Scheme 28)or (Scheme 29). On LS400, if engine main relay has tested okay, disconnect cooling fan relay No. 3.
2. On all models, use an ohmmeter to check for continuity between relay terminals No. 1 and 3. (Scheme 31)-32. Check for continuity between relay terminals No. 2 and 4. Ensure continuity is not present between relay terminals No. 4 and 5. If continuity is not as specified, replace relay.
3. Apply battery voltage between relay terminals No. 1 and 3. Using an ohmmeter, check for continuity between relay terminals No. 4 and 5. Ensure continuity is not present between relay terminals No. 2 and 4. If continuity readings are not as specified, replace relay.

COOLING FAN RELAY NO. 1 (ES250 & LS400) & NO. 2 (LS400)

1. Disconnect cooling fan relay No. 1. (Scheme 28)or (Scheme 29). On LS400, if cooling fan relay No. 1 has tested okay, disconnect cooling fan relay No. 2.
2. On all models, use an ohmmeter to check for continuity between relay terminals No. 1 and 2. (Scheme 31)-32. Check for continuity between relay terminals No. 3 and 4. If no continuity exists, replace associated cooling fan relay.
3. Apply battery voltage between relay terminals No. 1 and 2. Using an ohmmeter, ensure continuity is not present between relay terminals No. 3 and 4. If continuity is present, replace relay.

ES250 COOLING FAN RELAY NO. 2

1. Disconnect cooling fan relay No. 2. (Scheme 28) Using an ohmmeter, check for continuity between relay terminals No. 2 and 6. (Scheme 31)-32.
2. Check for continuity between relay terminals No. 1 and 3. Ensure continuity is not present between relay terminals No. 1 and 4. If continuity readings are not as specified, replace relay.
3. Apply battery voltage between relay terminals No. 2 and 6. Using an ohmmeter, ensure no continuity exists between relay terminals No. 1 and 3. Check for continuity between terminals No. 1 and 4. If continuity is not as specified, replace relay.

ES250 COOLING FAN RELAY NO. 3

Remove cooling fan relay No. 3. (Scheme 28) Testing procedures for ES250 cooling fan relay No. 3 are same as for ES250 & LS400 EFI main relay. See EFI MAIN RELAY under RELAYS.

COOLING FAN MOTORS NO. 1 & NO. 2

Disconnect cooling fan electrical connector. Connect vehicle battery with an ammeter in series to cooling fan connector. (Scheme 37) Ensure cooling fans operate smoothly. Ammeter reading should not exceed specifications in COOLING FAN AMPERAGE table.

COOLING FAN AMPERAGE

Scheme 37

FAILURE SYMPTOMS & CIRCUIT TESTS

1. Determine failure symptom. Proceed to indicated circuit test.
2. If theft deterrent or door lock control functions cannot be set or activated, go to appropriate THEFT DETERRENT ECU POWER CIRCUIT TEST.
3. If theft deterrent system does not deactivate when ignition switch is turned to ON or ACCESSORY position, go to appropriate THEFT DETERRENT IGNITION SWITCH CIRCUIT TEST.
4. If starter does not operate even when theft deterrent system is deactivated, go to appropriate THEFT DETERRENT STARTER CUT SYSTEM CIRCUIT TEST.
5. If theft deterrent system does not unlock doors when key is left in ignition switch (key confinement prevention), go to appropriate THEFT DETERRENT KEY UNLOCK WARNING SWITCH CIRCUIT TEST.

Note. For theft deterrent ECU terminal and circuit identification (Scheme 38)or (Scheme 39) and appropriate THEFT DETERRENT ECU TERMINAL IDENTIFICATION table.

ES250 THEFT DETERRENT ECU TERMINAL ID

Scheme 38

LS400 THEFT DETERRENT ECU TERMINAL ID

Scheme 39

ES250 THEFT DETERRENT ECU POWER CIRCUIT TEST

1. Turn ignition off. Check 20-amp DOME fuse in junction block No. 2. (Scheme 28) Replace fuse if necessary. If system operation is still abnormal after replacing fuse, repair wire harness between ECU connector terminal A6 and DOME fuse.
2. If fuse was okay in step 1), disconnect theft deterrent ECU connectors. Theft deterrent ECU is located under right side of dash, behind glove box. Using a DVOM, check for battery voltage between connector terminal A6 and ground. (Scheme 38)
3. If battery voltage is not present, repair harness and connector between DOME fuse and theft deterrent ECU. If battery voltage is present, check for continuity between harness connector terminal B14 and ground. Repair ground or harness as necessary.
4. If ground circuit is okay, check following function circuits. Repair circuit(s) as necessary. If all function circuits are okay, replace ECU, and retest system.

LS400 THEFT DETERRENT ECU POWER CIRCUIT TEST

1. Turn ignition off. Check 10-amp DOME fuse in junction block No. 2. (Scheme 29) Replace fuse if necessary. Check for a short in all circuits related to DOME fuse. Repair circuit(s) as necessary.
2. If fuse was okay in step 1), disconnect ECU harness connectors. Theft deterrent ECU is located under left side of dash, above junction block No. 1. Using a DVOM, check for battery voltage between ECU harness connector terminals A20 and A16. (Scheme 39) If okay, go to next step. If battery voltage is not present, go to step 5).
3. Check DOOR circuit breaker in junction block No. 1. If circuit breaker is open, check for shorts in all circuits related to DOOR circuit breaker. Repair circuit(s) as necessary.
4. Check actuator motors and solenoids for operation by applying battery voltage to solenoid or motor connectors for one to 2 seconds. Repair or replace as necessary.
5. If battery voltage is not present in step 2), check for continuity between harness connector terminal A16 and body ground. Repair ground or harness as necessary.
6. If ground circuit is okay, check and repair related wire harness between ECU connector terminal A20 and battery. If all circuits are okay, replace ECU, and retest system.

ES250 THEFT DETERRENT IGNITION SWITCH CIRCUIT TEST

1. Turn ignition off. Check 15-amp ECU-IG fuse. ECU-IG fuse is located in junction block No. 1 in driver-side kick panel area. If fuse is bad, repair short in wire harness between ECU-IG fuse and theft deterrent ECU terminal B2. (Scheme 38) If fuse is okay, go to next step.
2. Disconnect theft deterrent ECU connectors. Theft deterrent ECU is located under dash, above glove box. Turn ignition switch to ON position. Using a DVOM, check for battery voltage between theft deterrent ECU harness terminal B2 and body ground. (Scheme 38)
3. If battery voltage is not present, repair open circuit in wire harness between ECU-IG fuse and harness terminal B2. If battery voltage is present, replace theft deterrent ECU, and retest system.
4. Turn ignition off. Check 15-amp CIG fuse. CIG fuse is located in junction block No. 1 in driver-side kick panel area. If fuse is bad, repair short in wire harness between CIG fuse and theft deterrent ECU terminal A10. (Scheme 38) If fuse is okay, go to next step.
5. Disconnect theft deterrent ECU connectors. Theft deterrent ECU is located under dash, above glove box. Turn ignition switch to ON or ACC position. Using a DVOM, check for battery voltage between theft deterrent ECU harness terminal A10 and body ground. (Scheme 38)
6. If battery voltage is not present, repair open circuit in wire harness between CIG fuse and harness terminal A10. If battery voltage is present, replace theft deterrent ECU, and retest system.

LS400 THEFT DETERRENT IGNITION SWITCH CIRCUIT TEST

1. Turn ignition off. Check 15-amp ECU-IG and CIG fuses. ECU-IG and CIG fuses are located in junction block No. 1 in lower left side of dash. If a fuse is bad, go to next step. If fuses are okay, go to step 3).
2. If a fuse is bad, repair short in wire harness or components between related fuse and theft deterrent ECU terminals A2 (ECU-IG) and B7 (CIG). (Scheme 39) Theft deterrent ECU is located under left side of dash, above junction block No. 1.
3. Disconnect theft deterrent ECU connectors. Turn ignition switch to ON position. Using a DVOM, check for battery voltage between theft deterrent ECU harness terminals A2 and B7 and body ground. (Scheme 39)
4. If battery voltage is not present, repair open circuit in wire harness between harness terminals A2 and B7 and battery. If battery voltage is present, replace theft deterrent ECU, and retest system.

ES250 THEFT DETERRENT KEY UNLOCK WARNING SWITCH CIRCUIT TEST

1. Turn ignition off. Disconnect theft deterrent ECU connectors. ECU is located under dashboard, above glove box. Ensure ignition key is in ignition switch.
2. Using a DVOM, check for continuity between theft deterrent ECU harness terminal B6 and ground. (Scheme 38) If continuity is not present, check for short or open in key unlock warning switch circuit. If continuity is present, replace theft deterrent ECU, and retest system.

LS400 THEFT DETERRENT KEY UNLOCK WARNING SWITCH CIRCUIT TEST

1. Turn ignition off. Disconnect theft deterrent ECU connectors. Theft deterrent ECU is located under left side of dash, above junction block No. 1. Ensure ignition key is in ignition switch.
2. Using a DVOM, check for continuity between theft deterrent ECU harness terminal A6 and ground. (Scheme 39) If continuity is not present, check for short or open circuit in key unlock warning switch circuit. If continuity is present, replace theft deterrent ECU, and retest system.

ES250 THEFT DETERRENT STARTER CUT SYSTEM CIRCUIT TEST

1. If starter does not operate even after theft system has been deactivated, use key to turn front door lock to unlock position. Recheck starter operation. If starter still does not operate, go to next step.
2. Disconnect theft deterrent ECU connectors. ECU is located under dashboard, above glove box. Ensure shift lever is in Neutral or Park, or clutch pedal is depressed. Turn ignition switch to START position. Using a DVOM, check for battery voltage between ECU connector harness terminal B1 and ground. (Scheme 38)
3. If battery voltage is present, replace theft deterrent ECU, and retest system. If battery voltage is not present, repair short or open in starter relay circuit. Ensure starter relay operation is correct. See «STARTER RELAY»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__starter-relay) under RELAYS. Also, see ES250 CLUTCH START SWITCH or NEUTRAL START SWITCH under «ENGINE SENSORS & SWITCHES»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests).

LS400 THEFT DETERRENT STARTER CUT SYSTEM CIRCUIT TEST

1. If starter does not operate even after theft system has been deactivated, use key to turn front door lock to unlock position. Recheck starter operation. If starter still does not operate, go to next step.
2. Disconnect theft deterrent ECU connectors. ECU is located under left side of dash, above junction block No. 1. Ensure shift lever is in Neutral. Turn ignition switch to START position. Using a DVOM, check for battery voltage between ECU connector harness terminal A1 and ground. (Scheme 39)
3. If battery voltage is present, replace theft deterrent ECU, and retest system. If battery voltage is not present, repair short or open between ECU harness connector terminal A1 and the starter relay. Refer to «STARTER RELAY»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__starter-relay) under RELAYS. Also, refer to «NEUTRAL START SWITCH»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__neutral-start-switch) under ENGINE SENSORS & SWITCHES.

LS400 THEFT DETERRENT ECU OPERATION TEST

1. If no malfunction is found in circuit tests, check theft deterrent ECU operation and ground circuit. Theft deterrent ECU is located under left side of dash, above junction block No. 1.
2. Connect theft deterrent ECU connectors. Close all vehicle doors. Turn ignition switch to ON position. Use DVOM at rear of ECU connector. Check for battery voltage between theft deterrent ECU harness connector terminal B8 and ground. (Scheme 39)
3. Turn ignition switch to OFF position. Battery voltage should be present between harness connector terminal B8 and ground for approximately 60 seconds after ignition switch has been turned off. Cycle ignition switch on and off. Battery voltage should remain at terminal B8 for at least 60 seconds.
4. Turn ignition switch to OFF position. Open front door within 60 seconds of turning ignition switch off. Battery voltage should not be present between harness connector terminal B8 and ground.
5. Close all doors, and turn ignition switch to ON position. Open front door. Battery voltage should be present between harness connector terminal B8 and ground. Turn ignition switch to OFF position. Voltage should not exist between ECU harness terminal B8 and ground. Check ground circuit, and replace ECU as necessary.

LS400 THEFT DETERRENT ECU GROUND CIRCUIT TEST

1. Connect theft deterrent ECU connectors (if disconnected). Using a DVOM, measure resistance between theft deterrent ECU connector terminal A16 and ground. (Scheme 39) Resistance should be one ohm or less.
2. If resistance is within specification, replace ECU with a known good unit, and retest system. If resistance is not within specification, disconnect theft deterrent ECU connector.
3. Check theft deterrent ECU ground terminal and wire harness connector for damage. Repair as necessary. If theft deterrent ECU ground terminal and wire harness connector are okay, replace theft deterrent ECU, and retest system.

CIRCUIT DIAGNOSIS CHARTS (LS400)

Note. Table is to be used for identification of EFI ECU connector terminals in CIRCUIT DIAGNOSIS CHARTS .

EFI ECU TERMINAL IDENTIFICATION

EFI ECU TERMINAL IDENTIFICATION

CIRCUIT DIAGNOSIS CHARTS

Note. Following CIRCUIT DIAGNOSIS CHARTS are courtesy of Toyota Motor Sales, U.S.A., Inc.

Neutral Start Switch Circuit (1 of 2). Scheme 40

Neutral Start Switch Circuit (2 of 2). Scheme 41

ECU Power Source Circuit (1 OF 4). Scheme 42

ECU Power Source Circuit (2 OF 4). Scheme 43

ECU Power Source Circuit (3 OF 4). Scheme 44

ECU Power Source Circuit (4 OF 4). Scheme 45

Back-Up Power Source Circuit. Scheme 46

Injector Circuit (1 of 2). Scheme 47

Injector Circuit (2 of 2). Scheme 48

Cold Start Injector Circuit (1 of 2). Scheme 49

Cold Start Injector Circuit (2 of 2). Scheme 50

Fuel System Circuit (1 of 5). Scheme 51

Fuel System Circuit (2 of 5). Scheme 52

Fuel System Circuit (3 of 5). Scheme 53

Fuel System Circuit (4 of 5). Scheme 54

Fuel System Circuit (5 of 5). Scheme 55

Fuel Pressure Control Vacuum Sw. Valve Circuit (1 of 2). Scheme 56

Fuel Pressure Control Vacuum Sw. Valve Circuit (2 of 2). Scheme 57

Terminal TE1 & TE2 Circuit Diagnosis. Scheme 58

A/C Compressor Circuit (1 of 3). Scheme 59

A/C Compressor Circuit (2 of 3). Scheme 60

A/C Compressor Circuit (3 of 3). Scheme 61

See also:
• CIRCUIT DIAGNOSIS CHARTS
• AIRFLOW METER AIR TEMPERATURE SENSOR RESISTANCE
• AIRFLOW METER
• LS400 A/C PRESSURE SWITCH
• EFI MAIN RELAY
• STARTER RELAY
• NEUTRAL START SWITCH