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.
Warm Up Three-Way Catalytic Converter: Inspection
1999 Mazda 626 ES, 2.5 D, StandardSECTION Inspection
WARNING: This page is about a different car, the 2003 Mazda Protege5, 2003 Mazda Protege, 2003 Mazda MX-5 Miata, 2003 Mazda MPV, and 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Ensure no HO2S DTC has been detected. If detected, this inspection cannot be used.
- Using scan tool, access O2S11 (front HO2S) and O2S12 (rear HO2S) PIDs.
- Monitor appropriate PIDs.
- Drive vehicle for 10 minutes at 40-60 MPH to ensure Warm Up Three-Way Catalytic Converter (WU-TWC) reaches operating temperature.
- Stop vehicle, let engine idle and record PIDs for one minute.
- Select appropriate PIDs and read graph. See Fig 1 or Fig 2 .
- Count number of times graphline actually crosses .5V line (inversion) for both front and rear HO2Ss.
- Divide number of front HO2S inversions by number of rear HO2S inversions for ratio data.
- If ratio is 2 (1.5 on Mazda6) or more or no rear HO2S inversions, WU-TWC converter is functioning properly.
- If ratio is less than 2 (1.5 on Mazda6), WU-TWC converter has deteriorated. See Fig 3. Replace faulty WU-TWC converter.
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.