Engine Controls - System/component Tests: Diagnosis Lexus LS II

Circuit Description

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, battery voltage 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)

1. Connect Lexus scan tool to Data Link Connector (DLC) No. 3. Turn scan tool on. Turn ignition on. Using scan tool, read STA signal with ignition on and then while cranking starter.
2. 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»(ref-22205) article.
3. Check for open in wiring harness between ECM and starter relay. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22206) article. Repair as necessary. If wiring is okay, replace ECM and retest.

Diagnosis & Repair (Using OBD-II Scan Tool)

1. Access ECM harness connectors behind glove box. While backprobing ECM harness connector, measure voltage between ground and terminal No. 13 (Black wire) at ECM E14 connector.
2. 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»(ref-22205) article.
3. Check for open in wiring harness between ECM and starter relay. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22206) article. Repair as necessary. If wiring is okay, replace ECM and retest.

Test Procedure No. 1

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

Test Procedure No. 2

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

Test Procedure No. 3

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

RELAY TYPE & TEST PROCEDURE NUMBER

Scheme 10

Scheme 11

Scheme 12

Scheme 13

Scheme 14

Resistance Test

Disconnect EGR valve connector. See appropriate illustration in VACUUM DIAGRAMS article. Measure resistance between the following terminals of EGR valve connector. see scheme 23

1. Terminals B1 and S1.
2. Terminals B1 and S3.
3. Terminals B2 and S2.
4. Terminals B2 and S4.

If resistance is not 19.9-23.4 ohms at 68°F (20°C), replace EGR valve. If resistance is 19.9-23.4 ohms, check EGR valve operation.