What this code means

The ECU detected that the heater resistance in the downstream oxygen sensor on Bank 1 is outside the expected range. The downstream sensor monitors catalytic converter efficiency and requires proper heater function.

Symptoms

• Check Engine Light
• Failed emissions test
• Poor catalyst monitoring
• Slightly reduced fuel economy

Common causes

• Faulty downstream O2 sensor heater
• High resistance in heater wiring
• Corroded connector at sensor
• Heater relay failure

Diagnostic steps

1. Test downstream O2 sensor heater resistance
2. Inspect connector for corrosion
3. Check heater circuit wiring
4. Test heater relay operation

Repair notes

Replace the downstream O2 sensor on Bank 1.

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