Lexus IS250 · Service Manual ENGINE

ECM Power Source Circuit

Circuit diagnosis

DESCRIPTION

When the engine switch is turned to on, the battery voltage is applied to terminal IGSW of the ECM. The ECM MREL output signal causes a current to flow to the coil, closing the contacts of the EFI MAIN relay and supplying power to terminal +B of the ECM.
If the engine switch is turned to off, the ECM holds the EFI MAIN relay ON for a maximum of 2 seconds to allow for the initial setting of the throttle valve.
When the engine switch is turned on (IG), voltage from the ECM's MREL terminal flows to the integration relay (EFI MAIN relay). This causes the contacts of the integration relay (EFI MAIN relay) to close, which supplies power to terminal +B or +B1 of the ECM.

WIRING DIAGRAM

A122749E01
A122750E01

INSPECTION PROCEDURE


1. INSPECT ECM (+B, +B1 VOLTAGE)

  1. A124678E17
    Turn the engine switch on (IG).

  1. Measure the voltage of the A5 and E4 ECM connectors.

    Standard voltage:
    Tester Connection
    		 Specified Condition
    +B (A5-6) - E1 (E4-7)
    		 9 to 14 V
    +B1 (A5-5) - E1 (E4-7)
    		 9 to 14 V



OK
PROCEED TO NEXT INSPECTION PROCEDURE SHOWN IN PROBLEM SYMPTOMS TABLE
NG


2. CHECK HARNESS AND CONNECTOR (ECM - BODY GROUND)

  1. A107151E07
    Disconnect the E4 ECM connector.

  1. Measure the resistance of the wire harness side connector.

    Standard resistance (Check for open):
    Tester Connection
    		 Specified Condition
    E1 (E4-7) - Body ground
    		 Below 1 Ω

  1. Reconnect the ECM connector.



 NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK


3. INSPECT ECM (IGSW VOLTAGE)

  1. A124678E08
    Turn the engine switch on (IG).

  1. Measure the voltage of the A5 and E4 ECM connectors.

    Standard voltage:
    Tester Connection
    		 Specified Condition
    IGSW (A5-17) - E1 (E4-7)
    		 9 to 14 V



OK
Go to step 6
NG


4. CHECK FUSE (IGN FUSE)

  1. A107156E03
    Remove the IGN fuse from the cowl side junction block RH.

  1. Measure the resistance of the IGN fuse .

    Standard resistance:
    Below 1 Ω

  1. Reinstall the IGN fuse.



 NG
REPLACE FUSE
OK


5. INSPECT IG2 RELAY

  1. B016200E03
    Remove the IG2 relay from the engine room J/B and R/B No. 2.

  1. Measure the resistance of the IG2 relay.

    Standard resistance:
    Tester Connection
    		 Specified Condition
    3 - 5
    		 10 kΩ or higher
    3 - 5
    		 Below 1 Ω
    (when battery voltage applied to terminals 1 and 2)



NG
REPLACE IG2 RELAY
OK

CHECK AND REPAIR SMART ACCESS SYSTEM WITH PUSH-BUTTON START

6. INSPECT ECM (MREL VOLTAGE)

  1. A124678E09
    Turn the engine switch on (IG).

  1. Measure the voltage of the A5 and E4 ECM connectors.

    Standard voltage:
    Tester Connection
    		 Specified Condition
    MREL (A5-13) - E1 (E4-7)
    		 9 to 14 V



NG
REPLACE ECM
OK


7. CHECK FUSE (EFI FUSE)

  1. A107169E11
    Remove the EFI fuse from the engine room J/B and R/B No. 2.

  1. Measure the resistance of the EFI fuse.

    Standard resistance:
    Below 1 Ω

  1. Reinstall the EFI fuse.



 NG
REPLACE FUSE
OK


8. INSPECT INTEGRATION RELAY (EFI MAIN RELAY)

  1. A107714E08
    Remove the integration relay from the engine room J/B and R/B No. 2.

  1. Measure the resistance of the EFI MAIN relay.

    Standard resistance:
    Tester Connection
    		 Specified Condition
    2C-1 - 2A-8
    		 10 kΩ or higher
    Below 1 Ω
    (when battery voltage applied to terminals 2A-6 and 2A-7)



 NG
REPLACE INTEGRATION RELAY
OK


9. CHECK HARNESS AND CONNECTOR (INTEGRATION RELAY- ECM, INTEGRATION RELAY - BODY GROUND)

  1. A109879E04
    Check the harness and the connectors between the integration relay and the ECM.

    1. Remove the integration relay from the engine room J/B and R/B No. 2.

    2. Disconnect the A5 ECM connector.

    3. Measure the resistance of the wire harness side connectors.

      Standard resistance (Check for open):
      Tester Connection
      		 Specified Condition
      2A-6 - MREL (A5-13)
      		 Below 1 Ω

      Standard resistance (Check for short):
      Tester Connection
      		 Specified Condition
      2A-6 or MREL (A5-13) - Body ground
      		 10 kΩ or higher

  1. Check the harness and the connectors between the integration relay and body ground.

    1. Remove the integration relay from the engine room J/B and R/B No. 2.

    2. Measure the resistance of the wire harness side connector and body ground.

      Standard resistance (Check for open):
      Tester Connection
      		 Specified condition
      2A-7 - Body ground
      		 Below 1 Ω



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

CHECK AND REPAIR HARNESS AND CONNECTOR (TERMINAL +B OF ECM - BATTERY POSITIVE TERMINAL)


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