P0151 Subaru HO2S21 Sensor Circuit Low Voltage

Possible causes

– Faulty Front Heated Oxygen Sensor Bank 2
– Front Heated Oxygen Sensor Bank 2 harness is open or shorted
– Front Heated Oxygen Sensor Bank 2 circuit poor electrical connection
– Inappropriate fuel pressure
– Faulty fuel injectors
– Intake air leaks may be faulty
– Exhaust gas leaks

Tech description

Replacing the Front Heated Oxygen Sensor Bank 2 usually takes care of the problem

What about the obd code?

The voltage signal from the sensor is lower than the specified time.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– High Fuel Consumption
– Excessive smoke from Exhaust

P0151 Subaru Description

The front heated oxygen sensor (or O2 sensor 1) is placed into the exhaust manifold. It detects the amount of oxygen in the exhaust gas compared to the outside air. The heated oxygen sensor 1 has a closed-end tube made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions. The heated oxygen sensor 1 signal is sent to the Engine Control Module (ECM). The ECM adjusts the injection pulse duration to achieve the ideal air-fuel ratio. The ideal air-fuel ratio occurs near the radical change from 1V to 0V.