Does the downstream O2 sensor affect performance?

No — it only monitors the catalytic converter. Performance and fuel economy are not affected.

What should downstream O2 voltage be?

A healthy downstream O2 should read a fairly steady 0.4-0.7V. Rapid oscillation like the upstream sensor indicates a failing catalytic converter.

Low Severity

Emissions System

General fault with the downstream (post-cat) O2 sensor on bank 1. This sensor monitors catalytic converter efficiency.

Common Fix

Replace downstream O2 sensor

Estimated Cost (DIY)

$25 - $80

Faulty downstream O2 sensorlikely

Wiring damage from exhaust heatpossible

Contaminated sensorpossible

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Does the downstream O2 sensor affect performance?: No — it only monitors the catalytic converter. Performance and fuel economy are not affected.
What should downstream O2 voltage be?: A healthy downstream O2 should read a fairly steady 0.4-0.7V. Rapid oscillation like the upstream sensor indicates a failing catalytic converter.

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