Titania Lambda Sensor TTL1.0
What it does
The lambda sensor is a post engine oxygen sensor
fitted into the exhaust system of a vehicle and measures
the amount of oxygen in the exhaust stream. It signals
the ECU (Electronic Control Unit) with a voltage signal
relevant to this oxygen level. The ECU interprets
this as in indication of the vehicles mixture strength.
It is an essential part of the vehicles engine management
system and the longevity of the catalytic converter
is dependant upon its correct operation.
How do they work?
A flat, multi layer, blade type element constructed
of a material known as Aluminium titanate (TiO2 also
known as Titanium Dioxide) is housed in a stainless
steel casing and protected by a steel guard that allows
gases to pass through. The sensor is screwed into
the exhaust manifold or down pipe of a vehicle such
that its tip is in the exhaust flow.
One of the properties of aluminium titanate is that
its resistance changes when subjected to differing
oxygen concentrations. This property is used by lambda
manufactures to construct a sensor that, when fitted
into the exhaust system, signals the EMS ECU with
a voltage relevant to the mixture level.
The sensor’s tip incorporates a heater element.
The heater element is essential to the operation of
the lambda sensor. All Titania sensors incorporate
a heater element hence are only available in three
or four wire configurations, and the most common wire
colours are;
• Red = Heater positive (also ref in on three
wire sensor)
• Yellow = Reference voltage in
• Black = Reference voltage out (output wire)
• White = Heater negative (earth)
The Titania sensor is much more flexible with temperature
requirement than the Zirconia type sensor and generally
has an operating temperature of between 250 and 600
degrees centigrade. The sensor is supplied with a
constant voltage (normally 5v) and once its up to
operating temperature it responds to the oxygen content
with varying resistance and hence a varying output
voltage signal (normally 1 – 5 Volt) 5 volts
indicating a rich mixture.
Reasons for failure
Titania lambda sensors are inherently more reliable
than Zirconia sensors there are two principle areas
of failure:
Heater element failure, results in an elongated warm
up period, increased emissions from cold and possible
catalytic converter damage.
Sensor element pollution, the porous ceramic tips
becomes blocked/polluted and results in poor response
to mixture changes or in extreme cases total failure.
The pollution can be as a result of chemical pollution
i.e. exhaust paste, antifreeze or gasket sealant or
due to excessive carbon build up due to engine wear
or extended service life.
Testing
The heater can be checked with an Ohm meter and comparing
the reading to known data. A heater failure usually
results in an open circuit heater element, thus rendering
the heater completely inoperative.
Check output circuit response time by monitoring output
voltage with varying engine load (blip throttle).
There should be an almost instantaneous response.
Output voltage can be measured with either a voltmeter
or an oscilloscope and should be in the region of
2 to 5 volts fluctuating.
Output response time errors cause common MOT failures.
The lambda sensor will not react quick enough to changing
engine loads and speeds, hence
at MOT when the emissions are being checked at a fast
idle level the emission levels will rise above the
legal limit before settling back down to, possibly
pass the second fast idle test. The cause of this
fault is almost always the lambda sensor.
Off the car testing is not practical with Titania
sensors.
Note
Some vehicle manufacturers (Nissan, Jeep and Subaru)
use a lower output (0-1 volt) Titania sensor. The
methods of testing remain the same but for the lower
voltages. As a general guide it is unusual for Titania
sensors to be fitted to Japanese cars and to turbocharged
cars. Bosch do not make Titania sensors and therefore
cars with Bosch Injection systems (ECU) will not have
a Titania sensor fitted.
The most common applications for the Titania sensor
are the Vauxhall ECOTEC, Range Rovers and Jaguar
For further technical information
concerning lambda sensors please phone our technical
help line 01527 839307
