Possible causes

– Faulty Air-Fuel Ratio (A/F) Sensor Bank 2 Sensor 1
– Air-Fuel Ratio (A/F) Sensor Bank 2 Sensor 1 harness is open or shorted
– Air-Fuel Ratio (A/F) Sensor Bank 2 Sensor 1 circuit poor electrical connection
– Faulty Engine Control Module (ECM)

When is the code detected?

The P1155 is set when the Engine Control Module (ECM) detects a heated oxygen sensor heater circuit malfunction

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1155 TOYOTA Description

Air-Fuel Ratio (A/F)sensor need to reach a minimum operating temperature of 1200 degrees F to produce an accurate voltage signal. The faster the air-fuel ratio sensor reaches that temperature the faster the sensor will start sending an accurate signal to the Engine Control Module (ECM).
In order to achieve the require temperature, a heater element is included inside the air-fuel ratio sensor. The ECM controls the air-fuel ratio sensor heater element based on signals from the engine coolant temperature and engine load. The ECM controls the heater element circuit by allowing current flow to ground.
The ECM monitors the voltage signal received through the heater element circuit and determines the state of the circuit by comparing the voltage detected with the factory specifications.

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TOYOTA Technical Service Bulletins for P1155 code