Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
(Using Engine Signal Monitor)
1999 Mazda 626 ES, 2.5 D, StandardSECTION (Using Engine Signal Monitor)
WARNING: This page is about a different car, the 1997 Mazda Millenia. However, it is still accessible from the selected car via links, so may be relevant.
- Warm engine to normal operating temperature. Connect Engine Signal Monitor (49 9200 162A) to ECM, using proper overlay and adapter cables. Measure voltage of suspect sensor at ECM/PCM terminal. See HO2S ECM/PCM TERMINAL IDENTIFICATION table. Voltage should be .5-1.0 volt under acceleration and 0-.5 volt under deceleration.
- If voltage is not as specified, check wiring harness and connector between ECM and HO2S. Also check intake manifold system, fuel system and self-diagnostic system. Repair as necessary. If no problems are found, replace HO2S.
- To test HO2S heating element, allow sensor to cool to room temperature. Disconnect HO2S connector. Using ohmmeter, measure resistance between sensor terminals "B" and "C" for front sensor or terminals "C" and "D" for rear sensor. See Fig 1 . Resistance should be about 6 ohms with sensor temperature at 68°F (20°C). If resistance is not as specified, replace HO2S.
HO2S ECM/PCM TERMINAL IDENTIFICATION
| HO2S | ECM/PCM Terminal |
|---|---|
| Left Front Sensor | 3M |
| Left Rear Sensor | 3H |
| Right Front Sensor | 3I |
| Right Rear Sensor | 3D |
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.