What this code means

The PCM has detected that the upstream oxygen sensor on Bank 1 is responding too slowly during the catalytic converter efficiency monitor. The sensor switching rate is below the threshold needed for accurate catalyst monitoring.

Symptoms

• Check Engine Light
• Failed emissions test
• Slightly reduced fuel economy
• Possible rough idle

Common causes

• Aging or contaminated upstream O2 sensor
• Exhaust leak near the O2 sensor
• Wiring issue causing signal delay
• Fuel contamination affecting sensor response
• Catalytic converter deterioration affecting sensor readings

Diagnostic steps

1. Monitor O2 sensor switching frequency on scan tool (should switch rapidly at steady cruise)
2. Inspect O2 sensor wiring for damage or high resistance
3. Check for exhaust leaks near sensor location
4. Compare sensor response time to specification
5. Inspect catalytic converter condition

Repair notes

Replace the upstream O2 sensor Bank 1 if response time exceeds specification.

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