THE SENSE OF GOING
With a diverse range of throttle position sensors and throttle bodies, CAMBIARE shares some
The throttle body is integral to
combustion engines and controls
the amount of air that is let
into the engine during varying
operating conditions. Controlled
by the movement of the accelerator
pedal, the butterfly valve in the
throttle body was traditionally
operated mechanically by means
of a cable. The harder the pedal
was pushed, the wider the throttle
valve opens.
The ‘drive-by-wire’ system found in engines today have a throttle
position sensor which maintains the relationship between the driver’s
control of the accelerator pedal and the throttle body. The throttle
position sensor is used to monitor the position of the butterfly valve to
ensure that the throttle body actuator works in conjunction with the
accelerator pedal.
symptoms to manifest. Common issues caused by a failing throttle body
and/or throttle position sensor include:
• Car will not accelerate, lacks power when accelerating, or accelerates on
its own
• Engine will not idle smoothly, idles too slowly, or stalls
• Car accelerates but will not exceed a relatively low speed or shift up
• The ‘check engine light’ illuminates, accompanied by any of the above
behaviour
THE RIGHT COURSE OF ACTION
Due to the similarities of the symptoms shared between a problematic
throttle body and throttle position sensor, it is imperative that
technicians inspect the system thoroughly to ensure that they find the
root of the problem.
Detecting failures in throttle bodies
Lack of maintenance is one of the key causes of any system failure. This
is often due to accumulated contamination. The carbon particles and oil
mist in the vapour from the crankcase ventilation system of the engine
causes a build-up of carbon deposits within the throttle body. This
restricts the airflow and in extreme cases, may cause the valve to stick so
that adequate air cannot reach the engine.
Detecting failures in the throttle position sensors
A modern ‘drive-by-wire’ throttle pedal
A SYMBIOTIC RELATIONSHIP
The throttle position sensor continually measures the position of
the throttle butterfly and is combined with other data such as air
temperature, engine RPM, mass airflow and the speed of throttle
position changes which are monitored by the ECU. This information
precisely determines how much fuel is needed to be injected into
the engine at any given moment. A working throttle position sensor
creates a symbiotic relationship between the driver and the throttle
body, allowing the vehicle to accelerate, cruise or decelerate smoothly
and efficiently.
Given the working relationship between the throttle body and the
throttle position sensor, a fault in either part can cause similar
4 THROTTLE BODIES AND THROTTLE POSITION SENSORS
A failing throttle position sensor will hinder engine performance
because the air-to-fuel ratio will be compromised and it can fail
in several ways. All of which can result in poor fuel economy and
performance limitations. The sensor can fail gradually, or all at once.
When this happens, the ‘check engine light’ will likely be illuminated
and in the case of most modern vehicles, it will operate in “limp home”
mode of operation with reduced power if a failure is detected. This is
intended to allow the driver to safely get off a busy road when there is a
problem with the throttle position sensor.
Replacement upon failure
Throttle bodies and throttle
position sensors are non-
serviceable items. This means
that when there is any evidence of
failure, they need to be replaced. It
should be noted that the failure of
these components are not always
easily diagnosed. The only way to
ensure the correct diagnosis is by
carefully analysing the fault codes
via live data readings and visually
inspecting the part.
VITAL NEWS ISSUE 51