Air-Fuel Ratio Sensor Heater Circuit Malfunction Bank 2 Sensor 1 (Toyota)
What does P1155 mean?
The P1155 code means the vehicle's onboard diagnostic system has detected: Air-Fuel Ratio Sensor Heater Circuit Malfunction Bank 2 Sensor 1 (Toyota). This is a low severity code.
Common Symptoms
- Check Engine Light on
- Slightly poor fuel economy during warm-up
- Failed emissions test
- No significant drivability issues
- Extended closed-loop transition time
Probable Causes (Ranked by Likelihood)
- Failed air-fuel ratio sensor heater element Very High
- Blown A/F sensor heater fuse High
- Corroded sensor connector Moderate
- Wiring damage in heater circuit Moderate
- ECM heater driver fault Low
Step-by-Step Diagnostic Procedure
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Check the air-fuel ratio sensor heater fuse
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Measure heater resistance at the Bank 2 Sensor 1 connector
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Verify battery voltage reaches the heater circuit
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Inspect the sensor connector for moisture and corrosion
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Replace the air-fuel ratio sensor if the heater element has failed
Frequently Asked Questions
What is the difference between an air-fuel ratio sensor and an O2 sensor?
Toyota uses wideband air-fuel ratio (A/F) sensors as upstream sensors. These provide a linear voltage output for precise fuel control, unlike traditional narrow-band O2 sensors that only switch between rich and lean.
Are Toyota A/F sensors expensive?
Yes, Toyota A/F sensors are more expensive than standard O2 sensors. OEM Denso sensors typically cost $100 to $250 for the part. Aftermarket options are available for $60 to $150 but quality varies.
Can I use an aftermarket A/F sensor on a Toyota?
Aftermarket sensors can work, but Toyota vehicles are sensitive to sensor quality. Denso (OEM supplier) and NTK are recommended brands. Cheap generic sensors may trigger the code again or cause drivability issues.