Heated Oxygen Sensor: Miata

Voltage Inspection

Warm engine to normal operating temperature. Disconnect HO2S 4-pin harness connector. Connect voltmeter between ground and HO2S 4-pin connector terminal "A". See Fig 1 . Run engine at 3000 RPM until voltmeter indicates 0-1 volts. Ensure voltage changes within specification when engine RPM is increased or decreased several times. See HO2S VOLTAGE (MIATA) table. If voltage reading does not change as specified, replace HO2S. If HO2S is okay but PID value is not as specified, check for open or short circuit. See WIRING DIAGRAMS article. Go to next step.

HO2S VOLTAGE (MIATA)

Application	Volts
Acceleration	0.5-1.0
Deceleration	0-0.5

Fig 1: Identifying HO2S Connector - Terminal View (Miata)

Courtesy of MAZDA MOTORS CORP.

Open Circuit Inspection

Turn ignition switch off. Disconnect 31-pin harness connector. Check for open circuit. Check for continuity between following terminals:
- PCM harness connector terminal "4W" and front HO2S harness connector terminal "A" (Blue wire). See Fig 2 and Fig 3 .
- PCM harness connector terminal "4O" and front HO2S harness connector terminal "B" (Black/Red wire), through common connector.
- PCM harness connector terminal "4AA" and rear HO2S harness connector terminal "A" (Red wire).
- PCM harness connector terminal "4O" and rear HO2S harness connector terminal "B" (Black/Red wire), through common connector.
  
  Fig 2: Identifying PCM Connectors & Terminals (Miata)
  Courtesy of MAZDA MOTORS CORP.
  
  Fig 3: Identifying HO2S Harness Connector - Terminal View (Miata)
  Courtesy of MAZDA MOTORS CORP.
If continuity is not present, repair or replace wire harness as necessary. Go to next step.

Short Circuit Inspection

Check for continuity between ground and following PCM terminals:
- PCM 31-pin harness connector terminal "4W" (front HO2S). See Fig 2 .
- PCM 31-pin harness connector terminal "4AA" (rear HO2S)
If continuity is present, repair or replace wire harness as necessary.