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

FRONT 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.)

Front HO2S Current 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)

  • Front HO2S current (PID: O2S11)

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 front HO2S current (PID: O2S11) is 0.25 mA or more while decelerating as shown in the figure.

Front HO2S Heater Resistance Inspection

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

    Front HO2S heater resistance

  • 1—10 ohms

Front HO2S Circuit Open/Short Inspection

1. Disconnect the PCM connector. (See PCM REMOVAL/INSTALLATION [LF].)
2. Disconnect the front HO2S connector.
3. Inspect the following wiring harnesses for an open or short circuit. (Continuity inspection)

    Open circuit

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

    • Front HO2S terminal A and PCM terminal 2AD

    • Front HO2S terminal B and PCM terminal 2Z

    • Front HO2S terminal C ignition relay

    • Front HO2S terminal D and PCM terminal 2BG

    Short circuit

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

    • Front HO2S terminal A and power supply

    • Front HO2S terminal A and body ground

    • Front HO2S terminal B and power supply

    • Front HO2S terminal B and body ground

    • Front HO2S terminal C and body ground

    • Front HO2S terminal D and power supply

    • Front HO2S terminal D and body ground



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