SUBARU Forester Oxygen Sensor

Description

An oxygen sensor converts the status of the engine's exhaust gas oxygen content into a corresponding voltage signal. The oxygen sensor is sometimes referred to as a Lambda sensor on some European cars. Changes in the amount of exhaust gas oxygen result in a voltage change that is monitored by the vehicle's powertrain control module. Many oxygen sensors also have built-in heaters, to warm them to operating temperature more quickly. Prior to 1996, most vehicles had one oxygen sensor. After 1996 vehicle are equipped with two to four oxygen sensors.

Purpose

The SUBARU Forester oxygen sensor supplies real time information about the engine's exhaust gas oxygen content to the powertrain control module. This information is used primarily to help calculate fuel delivery to the engine, which changes continuously while it is running. If the engine is running lean, the powertrain control module will sense this from the oxygen sensor's signal and increase the fuel supplied to the engine. Conversely, just the opposite occurs when the engine begins to run rich. On OBDII-(1996 and later) equipped vehicles, the sensors are also used to help determine the efficiency of the catalytic converter. The powertrain control module does this by comparing the signal of the sensor located at the inlet of the catalytic converter with the signal of the sensor located at the outlet of the converter.

Maintenance Tips/Suggestions

SUBARU Forester oxygen sensors have a limited service period, replace as recommended in the owner's manual or when other conditions dictate, such as failing an emissions test or an oxygen sensor related diagnostic code from the powertrain control module indicating a faulty oxygen sensor. Some pre 1996 vehicles have an oxygen sensor light that appears when oxygen sensor replacement is needed.

Failure symptoms

Some symptoms of a faulty SUBARU Forester oxygen sensor include poor gas mileage, a failed emissions test, "rotten-eggs" smell from the exhaust, poor engine performance. A faulty oxygen sensor will cause the Service Engine Soon or Check Engine light to appear, it's best to have the cause checked out immediately by a professional technician.

WARNING

Neglecting these warning signs can cause expensive damage to the catalytic converter, requiring replacement.

AKA

O2 sensor, Lambda sensor, HEGO sensor, front (upstream) oxygen, rear (downstream) oxygen sensor

Location

On pre 1996 SUBARU Forester vehicles the oxygen is located in the exhaust manifold or front exhaust pipe near the exhaust manifold. Four cylinder has one oxygen sensor and V6 and V8 may has two, one for each engine bank. On 1996 SUBARU Forester and later OBDII equipped vehicles will have a least two oxygen sensors. An upstream or front oxygen sensor located in the exhaust system before the catalytic converter and a down stream or rear oxygen sensor located in the exhaust pipe after the catalytic converter. Some V6 and V8 equipped vehicles may have additional upstream and down stream oxygen sensors.

Disclaimer

Depending on the year and options your SUBARU Forester has, the above information may not apply. Consult with a professional automotive technician or manufacturer for specifics on your SUBARU Forester