Circuit Description
When ignition switch is turned on, 9-14 volts is applied to the terminal IGSW at ECM main relay control circuit, sending a signal to terminal M-REL at ECM switching EFI main relay on. On ES300, when ignition is turned off, ECM will keep EFI main relay on for 2 seconds or less in order to reset Idle Air Control (IAC) valve.
When engine is being cranked, intake air flow 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 16) 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 TESTS W/O CODES article.
- Check for open in wiring harness between ECM and starter relay. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM and retest.
Scheme 16
Diagnosis & Repair (Using OBD-II Scan Tool)
- Access ECM harness connectors behind glove box. Backprobing ECM harness connector, measure voltage between ground and terminal STA at ECM connector.
- 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 TESTS W/O CODES article.
- Check for open in wiring harness between ECM and starter relay. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM and retest.
Using Lexus Scan Tool
- Connect Lexus scan tool to Data Link Connector (DLC) No. 3. (Scheme 16) Turn ignition on. Turn scan tool on. DO NOT start engine.
- Select ACTIVE TEST mode on scan tool. Using Lexus scan tool manufacturer's instructions, activate electric fuel pump. On all models except SC400, fuel pump is operating if fuel pump operating sound can be heard or pulsations can be felt in fuel line near fuel filter. On GS300, check that fuel pressure pulsation damper screw rises when fuel pump operates. (Scheme 17)
- If fuel pump does not operate, check for faulty fusible link in engine compartment fuse/relay block, located at left side of engine compartment. Check for faulty AM2 (30-amp) in engine compartment fuse/relay block, located at left side of engine compartment, and IGN (5-amp) in instrument panel fuse block, located at left side of steering wheel. Check for faulty EFI main relay in engine compartment junction block, located at left front of engine compartment. Check for faulty fuel pump, ECM or poor wiring connections.
