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A2 Error Codes, 4-4-3 & 4-3-5 (front O2 and Catalytic errors) 850

posted by jeff w on Mon Aug 5 14:49 CST 2002
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last visit: Tue Jul 24 17:32 CST 2001

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I have recently had error codes pulled and reset for 425 & 435 (rear and front O2 Sensor failures). I have thorougly checked all of the vacuum lines and have not found a suspect elbow or other leak. After i went through that check i then performed the O2 Sensor removal and torch burn routine. This did leave the car feeling really peppy but i can feel a dip in the rpm when driving now. The decrease in rpm can be sliglthy seen on the tack when i am driving. It appears to be happening every 6-8 seconds too. Tonight i checked my codes again expecting to see nothing since the lambda light was not on in the car. To my surprise i found 2 more codes activated. They are for the front O2 sensor as well as for the "Three-way catalytic convertor (TWC) efficiency low". I am not sure if anyone else has has seen these codes before. My guess is i should replace the front O2 sensor now but i am concerned about the catalytic error that has now appeared.
Any help would be appreciated.
Thanks
Jeff W
1994 854 T5
1994 855 T5

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A2 Error Codes, 4-4-3 & 4-3-5 (front O2 and Catalytic errors) 850

posted by someone claiming to be Robert on Mon Aug 5 23:51 CST 2002 [RELATED]

435 is front O2 sensor slow so yes, replace it. As for 443, that's just a BS code that's thrown out when the fuel trim is out of range caused by either a bad O2 sensor, vacuum leaks or misfiring. Clear the codes after replacing the front O2 sensor and it shouldn't return. Don't think about replacing a cat conv due to codes in an 850.

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