Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P0155: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) Heater Circuit Malfunction: General Description
The front air/fuel ratio (A/F) sensor (bank 2, sensor 1) is installed in the exhaust manifold, and it detects oxygen content in the exhaust gas. The front A/F sensor outputs voltage to the powertrain control module (PCM). The PCM controls fuel injection duration by comparing the target air/fuel ratio with the front A/F sensor signal. The sensor includes the VS cell, the pump cell, the atmospheric reference cavity, the diffusion layer, and the heater, and it enables overall feedback control. The heater is controlled by the PCM and is energized when the sensor element temperature is low. It heats the sensor to stabilize the detection of oxygen content. The PCM monitors the front A/F sensor heater output (return check). A malfunction is detected if the return signals do not meet the command value (for heater activation) in the PCM for a set time or more and a DTC is stored.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.