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Diagnostic Procedures

  1. If QUICK TEST was not performed, go to QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed, go to next step.

  2. KOER DTC P1128

    Inspect front HO2S connectors for crossed circuits, stretched wires and wire harness not properly mounted. If connectors are okay, go to next step. If connectors are not okay, repair as necessary, go to step  4 .

  3. Verify Proper HO2S SIG Pin Location

    Disconnect PCM connector. Install breakout box, leaving PCM disconnected. Disconnect both front HO2S connectors. Measure resistance between appropriate breakout box terminal and appropriate HO2S harness connector:
    • HO2S11 (Front Right), breakout box terminal No. 60.
    • HO2S21 (Front Left), breakout box terminal No. 87.
    See Fig 1 . If resistance is less than 5 ohms, fault cannot be duplicated at this time. See INTERMITTENT  under SYSTEM TESTS. If resistance is 5 ohms or more, go to next step.
    Fig 1: HO2S Harness Connector Circuit Identification
    G95E35968Courtesy of MAZDA MOTORS CORP.

  4. Verify Trouble Shooting Of DTCs Completed

    Reconnect all electrical connectors. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If same DTC is present, replace faulty PCM. Repeat QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, go to applicable procedure for other DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no DTCs are set, trouble shooting is complete.
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