LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Subaru >> 2019 >> WRX STI >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System (Diagnostics) (STI) (4 Of 4) >> Diagnostic Procedure With Diagnostic Trouble Code (DTC) >> DTC P2257: Secondary Air System Control "A" Circuit LOW >> Notes
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC P2257: Secondary Air System Control "A" Circuit LOW: Notes

DTC detecting condition: 

Immediately at fault recognition

CAUTION: After servicing or replacing faulty parts, perform Clear Memory Mode Refer to ENGINE (DIAGNOSTICS) (STI)>CLEAR MEMORY MODE>OPERATION , and inspection mode Refer to ENGINE (DIAGNOSTICS) (STI)>INSPECTION MODE>PROCEDURE .

Wiring diagram: 

Engine Electrical System Refer to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

G12456928Courtesy of SUBARU OF AMERICA, INC.
  1. CHECK HARNESS BETWEEN ECM AND SECONDARY AIR PUMP RELAY CONNECTOR. 
    1. Turn the ignition switch to OFF.
    2. Disconnect the connector from ECM.
    3. Remove the secondary air pump relay.
    4. Measure the resistance of harness between ECM connector and secondary air pump relay connector.

    Connector & terminal 

    (B135) No. 27 - (F9) No. 13:

    Is the resistance less than 1 Ω?

    Yes:  Go to  2.

    No:  Repair the harness and connector.

    NOTE: In this case, repair the following item:
    • Open circuit in harness between ECM connector and secondary air pump relay connector
    • Poor contact of coupling connector
  2. CHECK HARNESS BETWEEN ECM AND SECONDARY AIR PUMP RELAY CONNECTOR. 

    Measure the resistance between ECM connector and chassis ground.

    Connector & terminal 

    (B135) No. 27 - Chassis ground:

    Is the resistance 1 MΩ or more?

    Yes:  Even if DTC is detected, the circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again.

    NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.

    No:  Repair the short circuit to ground in harness between ECM connector and secondary air pump relay connector.