Subaru P1149 Air/Fuel Ratio Sensor 1 Circuit Range/Performance

Possible causes

– Faulty Air/Fuel Ratio Sensor 1
– Air/Fuel Ratio Sensor 1 harness is open or shorted
– Air/Fuel Ratio Sensor 1 circuit poor electrical connection

Symptoms

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

P1149 Subaru ACURA OBD Code Description

The Air/Fuel Ratio (A/F) sensor 1 is installed in the exhaust system and detects oxygen content in the exhaust gas. The A/F sensor transmits output voltage to the Engine Control Module (ECM)/Powertrain Control Module (PCM). A heater for the sensor element is embedded in the A/F sensor (sensor 1). It is activated and heats the sensor to stabilize and speed the detection of oxygen content by controlling current flowing through the heater. An increase in the current levels off as the applied voltage to the element electrode reaches a certain range because the amount of oxygen which is led through the diffusion layer is limited. The current amperage is proportional to oxygen content in the exhaust gas, so the air/fuel ratio is detected by the measurement of the current amperage. The ECM/PCM compares a set target air/fuel ratio with the detected air/fuel ratio and controls the fuel injection timing.

If the A/F sensor (sensor 1) voltage is low, the air/fuel ratio is lean, and the ECM/PCM uses A/F feedback control to issue a Rich command. If the A/F sensor (sensor 1) voltage is high, the air/fuel ratio is rich, and the ECM/PCM uses A/F feedback control to issue a Lean command.

If the element is not activated or the ECM/PCM terminal voltage is a set value or less for at least a set time period when the power is drawn to the A/F sensor (sensor 1) heater, a malfunction is detected and a DTC is stored.