Cause
Aged or lazy downstream oxygen sensor
The sensor behind the catalytic converter, whose job is to sit relatively still — a steady signal is what proves the converter is working. A lazy sensor produces exactly the flat trace a healthy converter should, so it can hide a failed converter, and a sluggish one can equally condemn a good one. Any catalyst verdict is worthless until this sensor is known to be good.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (13)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0420 Catalyst System Efficiency Below Threshold — Bank 1 Likely for this code Moderate
- P0421 Catalyst 1 Efficiency Below Threshold Bank 1 Likely for this code Moderate
- P0422 Catalyst 2 Efficiency Below Threshold Bank 1 Likely for this code Moderate
- P0430 Catalyst System Efficiency Below Threshold — Bank 2 Likely for this code Moderate
- P0431 Catalyst 1 Efficiency Below Threshold Bank 2 Likely for this code Moderate
- P0432 Catalyst 2 Efficiency Below Threshold Bank 2 Likely for this code Moderate
- P2096 Post Catalyst Fuel Trim System Too Lean — Bank 1 Likely for this code Moderate
- P2097 Post Catalyst Fuel Trim System Too Rich — Bank 1 Likely for this code Moderate
- P2098 Post Catalyst Fuel Trim System Too Lean — Bank 2 Likely for this code Moderate
- P2099 Post Catalyst Fuel Trim System Too Rich — Bank 2 Likely for this code Moderate
- P2379 O2 Sensor Out of Range During Deceleration Bank 2 Sensor 2 Likely for this code Moderate
- P0423 Heated Catalyst Efficiency Below Threshold — Bank 1 Moderate
- P0433 Heated Catalyst Efficiency Below Threshold — Bank 2 Moderate
Information, not instruction
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