Switch (TS) is invariable a three wire device operating at 5 volts (12 volts on
very early systems). The objective of the throttle switch is to inform the
Electronic Control Module (ECM) of the position of the throttle movement at
This device can
be switched in several ways, so it will be necessary to check with the vehicle
and module specific data. Inside the switch there are two sets of contacts, this
enables three stages of throttle movement to be monitored.
Throttle part open
Throttle fully open (sometimes referred to as wide open throttle - WOT )
waveform shows a dual trace picture, monitoring the two switched terminals of
the TS. The throttle has been operated from rest to full throttle and back to
rest. The blue trace is the idle contact circuit, once the throttle starts
operating this switch opens and its voltage changes from 0 to 5 volts. It will
remain at 5 volts, even at full throttle, until the throttle is back at its idle
red trace is the full load circuit and is at 5 volts (in its open position)
until full throttle is achieved. As the operator only stayed in the full
throttle position for a very short period (560 ms) the switch soon opens again
and the voltage changes back from 0 to 5.
switch is a 3 wire twin contact device that is operated by the throttle
butterfly spindle. This will provide information to the Electronic Control
Module (ECM) for throttle closed, throttle open and wide open throttle position
(90% open). When the engine is at tick over the idle contacts are closed, as the
throttle is opened these contacts open, sending a signal to the ECM to indicate
cruise/part load condition. At the 90% wide open throttle position the other
contacts are closed and the signal is sent to the ECM to provide extra fuel
enrichment for acceleration.
- Pedal (Bosch Common Rail Diesel) Diagnostics
accelerator quickly from idle to full throttle and observe the oscilloscope.
The voltage on output 2 will be approximately half of that on output 1:
typically at full throttle, a voltage of 3.35v will be seen, as opposed to
1.6v on output 2.
connection procedure will allow both outputs from the sensor to be monitored
at the same time.
accelerator pedal sensor is used to communicate the driver's throttle
movements to the vehicles Engine Control Module (ECM).
is connected to the throttle via an auxiliary cable and actuates a twin output
potentiometer. This information is sent to the ECM to assess the amount of
fuel to inject.
outputs are constantly monitored against each other, any discrepancies will be
logged as a fault code and the malfunction indicator warning light will
- Position Potentiometer Diagnostics
or potentiometer is able to indicate to the Electronic Control Module (ECM)
the exact amount of throttle opening due to its linear output.
of modern management systems will employ this particular sensor, and is
located on the throttle butterfly spindle. This is a 3 wire device having a 5
volt supply, an earth connection and a variable output from the centre pin. As
the output is critical to the vehicle's performance, any 'blind spots' within
the internal carbon track's swept area, will cause 'flat spots' and
'hesitations'. This lack of continuity can be seen on an oscilloscope and will
enable the operator to plot the output voltage over its operational range,
showing any faulty areas.
throttle potentiometer should show a small voltage at the throttle closed
position, gradually rising in voltage as the throttle is opened and returning
back to its initial voltage as the throttle is shut. Although many throttle
position sensor voltages will be manufacturer specific, many are
non-adjustable and the voltage will be in the region of 0.5 to 1.0 volts at
idle rising to 4.0 volts (or more) with a fully opened throttle. For the full
operational range, a time scale around 2 seconds is used.
picture should be clean with no voltage 'drop out' at any particular point, as
this small discrepancy will be sufficient to cause a 'flat spot' under initial
As the output
is critical to the vehicle's performance, any 'blind spots' within the
internal carbon track's swept area, will cause flat spots and hesitations.
This lack of continuity can be seen on a multimeter, however the use of an
oscilloscope will enable the operator to plot the output voltage over its
operational range, showing any faulty areas. A good throttle potentiometer
with no faults should provide the waveform indicated above.