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 SPECIFICATIONS table. If voltage reading does not change as specified, replace HO2S. If HO2S is okay but PID value is not as specified, go to next step. - Open Circuit Inspection
Turn ignition off. Disconnect PCM 31-pin harness connector. See Fig 2 and Fig 3 . Check for continuity between following terminals:- PCM 31-pin harness connector terminal No. 4W and front HO2S 4-pin harness connector terminal "A" (Blue wire).
- PCM 31-pin harness connector terminal No. 4O and front HO2S 4-pin harness connector terminal "B" (Black/Red wire), through common connector.
- PCM 31-pin harness connector terminal No. 4AA and rear HO2S 4-pin harness connector terminal "A" (Red wire).
- PCM 31-pin harness connector terminal No. 4O and rear HO2S 4-pin harness connector terminal "B" (Black/Red wire), through common connector.
If continuity is present, go to next step. If continuity is not present, repair open circuit in suspect wire or replace wire harness. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS.
- Short Circuit Inspection
Check for continuity between following terminals:- PCM 31-pin harness connector terminal No. 4W (front HO2S) and HO2S 4-pin harness connector terminal "A" (Blue wire).
- PCM 31-pin harness connector terminal No. 4AA (rear HO2S) and HO2S 4-pin harness connector terminal "A" (Red wire).
If continuity is present, repair short circuit in suspect wire or replace wire harness.
- HO2S Heater Resistance Inspection
Disconnect HO2S 4-pin harness connector. Using DVOM, measure resistance between HO2S 4-pin connector terminals "C" and "D". HO2S heater resistance reading should be about 5.6 ohms (front HO2S) or about 15.7 ohms (rear HO2S). If resistance reading is not as specified, replace suspect HO2S. If HO2S heater is okay, but PID value is out of specification, go to next step. - Open Circuit Inspection
Check for continuity in following circuits:- GND circuit - Between HO2S 4-pin harness connector "D" and PCM 24-pin harness connector terminal No. 3J (Black/Orange wire) through common connector (Front).
- Power circuit - Between HO2S 4-pin harness connector terminal "C" (Black/White wire) and ignition switch (IG1) circuit through common connector (Front).
- GND circuit - Between HO2S 4-pin harness connector terminal "D" (White/Black wire) and PCM 24-pin harness connector terminal No. 3P (Rear).
- Power circuit - Between HO2S 4-pin harness connector terminal "C" (Black/White wire) and ignition switch (IG1) circuit through common connector (Rear).
If continuity is present, go to next step. If continuity is not present, repair open circuit in suspect wire or replace wire harness. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS.
- Short Circuit Inspection
Check for continuity to ground in following circuits:- HO2S 4-pin harness connector terminal "C" (Black/White wire) and ignition switch (IG1) through common connector (Front).
- HO2S 4-pin harness connector terminal "D" (Black/Orange wire) and PCM 24-pin harness connector terminal No. 3J through common connector (Front).
- HO2S 4-pin harness connector terminal "D" (White/Black wire) and PCM 24-pin harness connector terminal No. 3P (Rear).
If continuity is present, repair short circuit to ground in appropriate wire or replace wire harness as necessary.