Engine Controls - System & Component Testing: Diagnosis

Circuit Description

When ignition switch is turned on, 9-14 volts is applied to the terminal IGSW at ECM main relay control circuit. ECM then applies voltage to terminal MREL at ECM, switching EFI main relay on.

Diagnostic Procedure (GS300)

Access ECM in left front of engine compartment. Turn ignition on. Backprobing connector, connect DVOM negative lead to terminal No. 17 (Brown wire) at ECM E3 connector and positive lead to terminal No. 16 (Black/Red wire) at ECM E6 connector. (Scheme 186) If 9-14 volts is present, ECM power circuit is okay. Diagnose by symptom. See «SYMPTOMS»(ref-151782-S30294375292003010800000) in TROUBLE SHOOTING - NO CODES article. If 9-14 volts is not present, go to next step.
Check for an open circuit in Brown wire between ground and terminal No. 17 at ECM E3 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If wiring is okay, go to next step.
Measure voltage between chassis ground and terminal No. 9 (Black/Orange wire) at ECM E6 connector. If 9-14 volts is present, go to step 5. If 9-14 volts is not present, check IGN fuse in junction box behind left kick panel.
If fuse is blown, repair cause of blown fuse. If fuse is okay, check ignition switch. See appropriate STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. Replace ignition switch as necessary and retest. If ignition switch is okay, repair open circuit between battery and ignition switch, or between ignition switch and ECM.
Turn ignition on. Measure voltage between chassis ground and terminal No. 10 (Black/Yellow wire) at ECM E6 connector. If 9-14 volts is not present, replace ECM. If 9-14 volts is present, check EFI fuse (25-amp) located in engine compartment fuse/relay box, at right rear of engine compartment, behind strut tower. If fuse is okay, go to next step. If EFI fuse is blown, repair cause of blown fuse. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
Check EFI main relay located in engine compartment fuse/relay box, at right rear of engine compartment, behind strut tower. See «RELAYS»(ref-151784-S01613866602003010800000) under MOTORS, RELAYS & SOLENOIDS. If EFI main relay is okay, check circuit between chassis ground and terminal No. 10 at ECM E6 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If circuit is okay, repair circuit between battery and EFI fuse.

Scheme 186

Diagnostic Procedure (IS300)

Access ECM in left front of engine compartment. Turn ignition on. Backprobing connector, connect DVOM negative lead to terminal No. 17 (Brown wire) at ECM E6 connector and positive lead to terminal No. 16 (Black/Red wire) at ECM E3 connector. (Scheme 187) If 9-14 volts is present, ECM power circuit is okay. Diagnose by symptom. See «SYMPTOMS»(ref-151782-S30294375292003010800000) in TROUBLE SHOOTING - NO CODES article. If 9-14 volts is not present, go to next step.
Check for an open circuit in Brown wire between ground and terminal No. 17 at ECM E6 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If wiring is okay, go to next step.
Measure voltage between chassis ground and terminal No. 9 (Black/Orange wire) at ECM E3 connector. If 9-14 volts is present, go to step 5. If 9-14 volts is not present, check IGN fuse in fuse block behind passenger side kick panel.
If fuse is blown, repair cause of blown fuse. If fuse is okay, check ignition switch. See appropriate STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. Replace ignition switch as necessary and retest. If ignition switch is okay, repair open circuit between battery and ignition switch, or between ignition switch and ECM.
Turn ignition on. Measure voltage between chassis ground and terminal No. 10 (Black/Orange wire) at ECM E3 connector. If 9-14 volts is not present, replace ECM. If 9-14 volts is present, check EFI fuse located in engine compartment fuse/relay box at left front of engine compartment. If fuse is okay, go to next step. If fuse is blown, repair cause of blown fuse.
Check EFI main relay located in engine compartment fuse/relay box at passenger side firewall in engine compartment. See «RELAYS»(ref-151784-S01613866602003010800000) under MOTORS, RELAYS & SOLENOIDS. If EFI main relay is okay, check circuit between chassis ground and terminal No. 10 at ECM E3 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If circuit is okay, repair circuit between battery and EFI fuse.

Scheme 187

Diagnostic Procedure (GS430 & SC430)

Access ECM in left front of engine compartment. Turn ignition on. Backprobing connector, connect DVOM negative lead to terminal No. 7 (Brown wire) at ECM E3 connector and positive lead to terminal No. 6 (Black/Red wire on GS430; Black/White wire on SC430) at ECM E6 connector. (Scheme 188) If 9-14 volts is present, ECM power circuit is okay. Diagnose by symptom. See «SYMPTOMS»(ref-151782-S30294375292003010800000) in TROUBLE SHOOTING - NO CODES article. If 9-14 volts is not present, go to next step.
Check for an open circuit in Brown wire between ground and terminal No. 7 at ECM E3 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If wiring is okay, go to next step.
Measure voltage between chassis ground and terminal No. 17 (Black/Orange wire on GS430; Green/Black wire on SC430) at ECM E6 connector. If 9-14 volts is present, go to step 5. If 9-14 volts is not present, check IGN fuse in junction box behind left kick panel.
If fuse is blown, repair cause of blown fuse. If fuse is okay, check ignition switch. See appropriate STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. Replace ignition switch as necessary and retest. If ignition switch is okay, repair open circuit between battery and ignition switch, or between ignition switch and ECM.
Turn ignition on. Measure voltage between chassis ground and terminal No. 13 (Black/Yellow wire on GS430; Green/Orange wire on SC430) at ECM E6 connector. If 9-14 volts is not present, replace ECM. If 9-14 volts is present, check EFI fuse located in engine compartment fuse/relay box, at right rear of engine compartment, behind strut tower. If fuse is okay, go to next step. If EFI fuse is blown, repair cause of blown fuse.
Check EFI main relay located in engine compartment fuse/relay box, at right rear of engine compartment, behind strut tower. See «RELAYS»(ref-151784-S01613866602003010800000) under MOTORS, RELAYS & SOLENOIDS. If EFI main relay is okay, check circuit between chassis ground and terminal No. 13 at ECM E6 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If circuit is okay, repair circuit between battery and EFI fuse.

Scheme 188

Diagnostic Procedure (LS430)

Access ECM in left front of engine compartment. Turn ignition on. Backprobing connector, connect DVOM negative lead to terminal No. 7 (Brown wire) at ECM E6 connector and positive lead to terminal No. 6 (Black/White wire) at ECM E3 connector. (Scheme 189) If 9-14 volts is present, ECM power circuit is okay. Diagnose by symptom. See «SYMPTOMS»(ref-151782-S30294375292003010800000) in TROUBLE SHOOTING - NO CODES article. If 9-14 volts is not present, go to next step.
Check for an open circuit in Brown wire between ground and terminal No. 7 at ECM E6 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If wiring is okay, go to next step.
Measure voltage between chassis ground and terminal No. 17 (Black/Orange wire) at ECM E3 connector. If 9-14 volts is present, go to step 5. If 9-14 volts is not present, check IGN fuse in instrument panel junction box under left side of instrument panel.
If fuse is blown, repair cause of blown fuse. If fuse is okay, check ignition switch. See appropriate STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. Replace ignition switch as necessary and retest. If ignition switch is okay, repair open circuit between battery and ignition switch, or between ignition switch and ECM.
Turn ignition on. Measure voltage between chassis ground and terminal No. 13 (Pink/Black wire) at ECM E3 connector. If 9-14 volts is not present, replace ECM. If 9-14 volts is present, check EFI No. 1 fuse located in engine compartment fuse/relay box at left front of engine compartment. If fuse is okay, go to next step. If fuse is blown, repair cause of blown fuse.
Check EFI main relay located in engine compartment fuse/relay box at left front of engine compartment. See «RELAYS»(ref-151784-S01613866602003010800000) under MOTORS, RELAYS & SOLENOIDS. If EFI main relay is okay, check circuit between chassis ground and terminal No. 13 at ECM E3 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If circuit is okay, repair circuit between battery and EFI No. 1 fuse.

Scheme 189

When engine is being cranked, intake airflow is slow, so fuel vaporization is poor. A rich mixture is necessary to achieve good startability. While engine is being cranked, 9-14 volts is supplied to ECM terminal STA. Starter signal is mainly used to increase fuel injection pulse for starting injection control and after-start injection control.

Note. The following test assumes starter cranks normally with ignition in START position. If starter does not crank normally, check and repair starter circuit before continuing with this test.

Diagnosis & Repair (Using Lexus Scan Tool)

Connect Lexus scan tool to Data Link Connector (DLC) No. 3. (Scheme 190) Turn scan tool on. Turn ignition on. Using scan tool, read STA signal with ignition on and then while cranking starter.
With ignition on, STA signal should be off. With ignition switch in START position, STA signal should be on. If STA signal is not as specified, go to next step. If STA signal is as specified, no problem is indicated at this time. Diagnose by symptom. See «SYMPTOMS»(ref-151782-S30294375292003010800000) in TROUBLE SHOOTING - NO CODES article.
Check for open in wiring harness between ECM and starter relay. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If wiring is okay, replace ECM and retest.

Scheme 190

Diagnosis & Repair (Using OBD-II Scan Tool)

Access ECM at left front of engine compartment. Backprobing ECM connector, measure voltage between ground and following terminal: On GS300, terminal No. 2 (Black wire) at ECM connector E5. (Scheme 186) On IS300, terminal No. 2 (Black wire) at ECM connector E4. (Scheme 187) On GS430, terminal No. 12 (Black wire) at ECM connector E6. (Scheme 188) On LS430, terminal No. 12 (Blue/Orange wire) at ECM connector E3. (Scheme 189) On SC430, terminal No. 12 (White/Blue wire) at ECM connector E6. (Scheme 188) On all models, go to next step.
Turn ignition switch to START position. With starter being cranked, voltage should be 6 volts or more. If voltage is not as specified, go to next step. If voltage is as specified, no problem is indicated at this time. Diagnose by symptom. See «SYMPTOMS»(ref-151782-S30294375292003010800000) in TROUBLE SHOOTING - NO CODES article.
Check for open in wiring harness between ECM and starter relay. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If wiring is okay, replace ECM and retest.

Testing EFI Main, Starter & Circuit Opening Relays

For relay terminal identification (Scheme 191)or (Scheme 192). If relay continuity is not as specified, replace relay and retest system.

Continuity should exist between terminals No. 1 and 2.
Continuity should not exist between terminals No. 3 and 5.
Apply battery voltage across terminals No. 1 and 2. Continuity should exist between terminals No. 3 and 5.

Scheme 191

Scheme 192

Testing Fuel Pump Relay (IS300, LS430 & SC430)

For relay terminal identification (Scheme 193) If relay continuity is not as specified, replace relay and retest system.

Continuity should exist between terminals No. 1 and 2.
Continuity should not exist between terminals No. 3 and 4.
Apply battery voltage across terminals No. 1 and 2. Continuity should exist between terminals No. 3 and 4.

Scheme 193

Fuel Pump Control Circuit - IS300, LS430 & SC430 (Using Lexus Scan Tool)

Note. For information on engine immobilizer, see THEORY & OPERATION article.

CAUTION

If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES - LEXUS article in GENERAL INFORMATION.

Connect Lexus scan tool to DLC3. (Scheme 190) Check fuel pump system operation. See «FUEL PUMP OPERATION»(ref-151770-S25417298072003010800000) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel pump operates, go to step 8. If fuel pump does not operate, go to next step.
Using Lexus scan tool, select ACTIVE TEST mode. Locate fuel pump relay in underhood relay block mounted in front of driver's side strut tower. Listen for noise while activating fuel pump relay. If relay noise can be heard when activated, go to step 4. If relay can not be heard when activated, go to next step.
Check operation of fuel pump relay. See «TESTING FUEL PUMP RELAY (IS300, LS430 & SC430)»(ref-151784-S19490668422003010800000) in RELAYS under MOTORS, RELAYS & SOLENOIDS. Replace relay as necessary. If fuel pump relay is okay, go to next step.
Check for faulty fuel pump. See «FUEL PUMP RESISTANCE»(ref-151784-S22620672442003010800000) and «FUEL PUMP OPERATION (USING BATTERY VOLTAGE)»(ref-151784-S40776072172003010800000). Replace fuel pump as necessary. If fuel pump is okay, go to next step.
Check operation of circuit opening relay. See «TESTING EFI MAIN, STARTER & CIRCUIT OPENING RELAYS»(ref-151784-S17701145772003010800000) in RELAYS under MOTORS, RELAYS & SOLENOIDS. Replace relay as necessary. If circuit opening relay is okay, go to next step.
Check for open circuit in wiring or connectors between EFI main relay, circuit opening relay and ECM, between circuit opening relay and fuel pump relay, and between fuel pump relay and fuel pump. Also check for open circuit between fuel pump and ground. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If no problem is found, go to next step.
Access ECM at left front of engine compartment. Turn ignition on. Measure voltage between ground and following ECM terminal: On IS300, terminal No. 5 (Green/Yellow wire) at ECM connector E3. (Scheme 187) On LS430, terminal No. 14 (Green/Black wire) at ECM connector E3. (Scheme 189) On SC430, terminal No. 14 (Green/Black wire) at ECM connector E6. (Scheme 188) If voltage is 9-14 volts, no problem is indicated at this time. If voltage is not 9-14 volts, locate and repair open circuit between battery and ECM terminal listed. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
Locate fuel pump resistor under protective cover on driver's strut tower in engine compartment. Disconnect fuel pump resistor Black 2-pin connector. Measure resistance between resistor terminals. If resistance is not.30-.35 ohm at 68°F (20°C), replace resistor. If resistance is.30-.35 ohm, check for open circuit between fuel pump relay and fuel pump resistor, or fuel pump resistor and fuel pump. Repair as necessary. See appropriate WIRING DIAGRAMS article. If wiring is okay, replace ECM and retest.

Fuel Pump Control Circuit - IS300, LS430 & SC430 (Using OBD-II Scan Tool)