What is an Oxygen or Lambda sensor?
(or Lambda) sensors are key to the running of a modern petrol engine.
They monitor the exhaust gases and feed information back to the
engine management system to allow it to adjust the fuel mixture
and keep the engine running smoothly.
are fitted into the exhaust - generally one at the front of the exhaust
and one near the back. The front (or pre-cat) sensors provide the information
on which the car can base its fuelling decisions, whereas the back (or
post-cat) sensors confirm that the catalytic converter is working efficiently.
do you know if you have a fault?
oxygen sensor will normally work at best performance for approximately
If it starts to fail or is damaged, the readings provided to the
engine become inaccurate and the fuel mixture is then incorrectly
calculated - often leading to overfuelling.
sensor failure can be apparent in a number of ways:
emissions on an MOT test
Warning light on a dashboard
idling or stalling
equipment is a great way to determine the cause of an engine warning
light or running problem. The tools, such as our GCR05,
extract the fault code from the car and provide clues as to the
cause of the problem itself, for example, if an oxygen sensor fault
is reported, it might be showing:
circuit fault - referring to the wiring of the sensor, rather
than the sensor itself. Often caused by wires becoming loose or damaged.
heater fault - referring to a fault within the heater element
inside the sensor. This isn't serviceable, so the sensor would need
to be replaced.
range/performance fault or 'lack of switching' - referring to
a fault with the sensor itself. This normally indicates a sensor reaching
the end of its life or having been contaminated. As sensors can't
easily be cleaned, this sensor would normally need to be replaced.
addition to a fault code, the more advanced test equipment, such
as our EngineCheck Pro
system, can also display readings from the sensor itself.
the case of the most common type of sensor (Zirconia narrow-band),
the sensor voltage on a warm idling engine should produce a smooth
oscillating wave between 0 and 1 volt. The frequency of this wave
should increase as the car accelerates. This oscillation is also
referred to as 'switching' (as mentioned in fault codes discussion
Replacing a sensor
oxygen sensors are available in the aftermarket for most modern
cars - our online application
list for sensors contains hundreds of direct-fit parts.
are often very quick and easy to fit - normally requiring just
a 22m open-ended spanner. For tricky to reach or seized sensors,
there's also a specially designed
socket that'll make it much easier.