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P0420
2017 BMW 328i
BMW
Severity
Medium
Safe to Drive
Yes
Est. Time
1hr
Difficulty
Easy
SYMPTOM
Check engine light, no performance change
Why This Happens
BMW's downstream O2 sensors are known to drift out of calibration before the catalytic converter itself degrades, making sensor testing the correct first step.
VERIFIED FIX:
Downstream O2 sensor replaced
How It Was Diagnosed
BMW's downstream O2 sensors are known to drift out of calibration before the catalytic converter itself degrades, making sensor testing the correct first step.
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