What this code means

The PCM has detected that the upstream heated oxygen sensor on Bank 1 is switching between rich and lean too slowly. The sensor response time exceeds the maximum allowable threshold for accurate fuel control.

Symptoms

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

Common causes

• Aging O2 sensor with degraded response time
• O2 sensor contaminated with silicone or coolant
• Exhaust leak near sensor
• O2 sensor heater circuit issue
• Wiring causing signal delay

Diagnostic steps

1. Monitor O2 sensor switching rate on scan tool at steady 2500 RPM
2. Compare response time to specification
3. Check O2 sensor heater circuit operation
4. Inspect for exhaust leaks near sensor
5. Check sensor wiring for high resistance

Repair notes

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

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