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NC MX-5 Miata Workshop Manual
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2008 - MX-5 - Engine

REAR HEATED OXYGEN SENSOR (HO2S) INSPECTION [LF]

NOTE:

  • Before performing the following inspection, make sure to follow the procedure as indicated in the troubleshooting flowchart. (See HOW TO USE THIS MANUAL.)

Rear HO2S Voltage Inspection

1. Warm up the engine to normal operating temperature.
2. Using the M-MDS, monitor the following:

  • Vehicle speed (PID: VSS)

  • Engine speed (PID: RPM)

  • Rear HO2S voltage (PID: O2S12)

3. Drive the vehicle and decelerate the engine speed by releasing the accelerator pedal fully when the engine speed is 3,000 rpm or more.
4. Verify that the rear HO2S outputs a voltage of 0.6 V or more, one time or more, then verify that the rear HO2S voltage (PID: O2S12) is 0.3 V or less while decelerating as shown in the figure.

Rear HO2S Heater Resistance Inspection

1. Disconnect the rear HO2S connector.
2. Measure the rear HO2S resistance between terminals C and D.

    Rear HO2S heater resistance

  • 2—50 ohms

Rear HO2S Circuit Open/Short Inspection

1. Disconnect the PCM connector.
2. Disconnect the rear HO2S connector.
3. Inspect the following wiring harnesses for an open or short circuit. (Continuity inspection)
    Open circuit

  • If there is no continuity, there is an open circuit. Repair or replace the wiring harness.

    • Rear HO2S terminal A and PCM terminal 2Q

    • Rear HO2S terminal B and PCM terminal 2BH

    • Rear HO2S terminal C and ignition relay

    • Rear HO2S terminal D and PCM terminal 2BE

    Short circuit

  • If there is continuity in the following wiring harnesses, there is a short circuit. Repair or replace the wiring harness.

    • Rear HO2S terminal A and power supply

    • Rear HO2S terminal A and body ground

    • Rear HO2S terminal B and power supply

    • Rear HO2S terminal B and body ground

    • Rear HO2S terminal C and body ground

    • Rear HO2S terminal D and power supply

    • Rear HO2S terminal D and body ground



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