Possible causes
– Rear Air/Fuel Ratio Sensor Bank 1 Sensor 1 harness is open or shorted
– Rear Air/Fuel Ratio Sensor Bank 1 Sensor 1 circuit poor electrical connection
– Faulty Rear Air/Fuel Ratio Sensor Bank 1 Sensor 1
– Rear Air/Fuel Ratio Sensor Bank 1 Sensor 1 circuit poor electrical connection
– Faulty Rear Air/Fuel Ratio Sensor Bank 1 Sensor 1
Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
P2251 TOYOTA OBD Code Description
The rear air/fuel ratio (A/F) sensor (bank 1, sensor 1) is installed in the exhaust manifold and detects oxygen content in the exhaust gas. The rear A/F sensor transmits a signal to the powertrain control module (PCM), and it enables overall feedback control. The PCM controls fuel injection duration by comparing the target air/fuel ratio with the rear A/F sensor signal. When the VSB1 terminal voltage is more than a specified value for a predetermined time, the PCM detects a malfunction and stores a DTC.