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ABS Speed Sensor
Air Flow Meter / Sensor
Air Intake Pressure Sensor
Alternator Current and Voltage
Amplifier Earth
Camshaft Sensor
Carbon Canister Solenoid Valve
Crankshaft sensor
Coolant Temperature sensor
Diesel Glow Plugs
Digital ECM to Ignition Amplifier Signal
Distributor Pickup
Dual Trace
Electronic Fuel Pump
Exhaust Gas Recirculation
Idle Speed Control Valve
Injectors
Knock Sensor
Lambda Sensor
MAP Sensor
Primary
Relative Compression
Secondary
Supercharger
Throttle
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Throttle - Switch Diagnostics

The Throttle 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 throttle housing.

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.

These are:-
Throttle closed
Throttle part open
Throttle fully open (sometimes referred to as wide open throttle - WOT )

The example 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 position.

The 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.

Technical Information

The throttle 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.



Throttle - Pedal (Bosch Common Rail Diesel) Diagnostics


Snap the 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.

This connection procedure will allow both outputs from the sensor to be monitored at the same time.

Technical Information

The accelerator pedal sensor is used to communicate the driver's throttle movements to the vehicles Engine Control Module (ECM).

The component 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.

The twin outputs are constantly monitored against each other, any discrepancies will be logged as a fault code and the malfunction indicator warning light will illuminate.
Throttle - Position Potentiometer Diagnostics

This sensor or potentiometer is able to indicate to the Electronic Control Module (ECM) the exact amount of throttle opening due to its linear output.

The majority 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.

A good 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.

The 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 acceleration.
Technical Information

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.


A throttle potentiometer.