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General Smog Check

2002 Mazda Miata Check Engine Light Still ON

Bought this Mazda Miata a little over a year now, The owner did a smog check before he sold it to me. A day after I bought it, the check engine light came on. Two-three months later, I replaced both front and rear o2 sensors with no luck of the check engine light going off.

Now I bought a universal Catalytic converter from AutoZone made by magnaflow,"$280", took it in to get it welded on for $80, The OEM cat converter has an oxygen sensor port in the center of the CAT, This aftermarket ca legal cat converter didn't, so the shop made a custom hold right behind the cat to insert the o2 sensor. Check engine light is still on with the code of p0037, heater O2. Smog shop stated that's wrong cat, so I bought a new California legal Walker Cat. $260. Still same check engine code p0037. I already took the car in to get it diagnosed and shop stated it's the cat converter. Now what? Please any help will be appreciated. Thanks.


Two seperate issues here. The trouble code (P0037) as you've indicated is due to a problem with the particular oxygen sensor's heating element or the heating element's circuit. The circuit includes the engine control unit (ECU), entire oxygen sensor, and the wiring in-between. With that said, if a "circuit" problem exists having to do with other then the oxygen sensor, replacing the sensor will result in no correction. We'd recommend a smog check repair station conduct a thorough diagnosis of oxygen sensor and heating element circuit.

The OEM CAT problem hopefully is now corrected since you've replaced with a Walker California legal catalytic converter. Welding anything to the CAT these days is an automatic failure. Either it's got to be a factory part or an aftermarket with an EO stamp for specifically that vehicle.

posted by SmogTips Support

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