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.
The TOYOTA 4-Runner 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.
TOYOTA 4-Runner 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.
Some symptoms of a faulty TOYOTA 4-Runner 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
Neglecting these warning signs can cause expensive
damage to the catalytic converter, requiring replacement.
O2 sensor, Lambda sensor, HEGO sensor, front (upstream) oxygen, rear
(downstream) oxygen sensor
On pre 1996 TOYOTA 4-Runner 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 “MAKE
MODEL” 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.
Depending on the year and options your TOYOTA 4-Runner has, the
above information may not apply. Consult with a professional automotive
technician or manufacturer for specifics on your TOYOTA 4-Runner