P0133: O2 Sensor Circuit Slow Response — Bank 1 Sensor 1
What to do
Economy will have declined gradually, often unnoticed. This usually does mean the sensor genuinely needs replacing, and it is one of the more clear-cut oxygen sensor codes.
What this code means
A healthy upstream sensor switches between rich and lean many times per second. This code says it still switches, but sluggishly — the classic signature of an aged sensor whose element has been progressively poisoned by silicone, oil or coolant over many miles. Slow response is a wear-out mode rather than a failure, which is why it appears on high-mileage vehicles with no other symptom than a gradual drift in economy.
Likely causes
Start here
Less common
- Exhaust leak before the sensor · moderate
- Failed oxygen sensor heater element · easy
Rare
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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