The purpose of this test is to investigate the operation of the idle and full throttle position switches.
These known good waveforms have the following characteristics:
Channel A indicates the operation of the (normally closed) idle position switch.
Channel B indicates the operation of the (normally open) full-throttle position switch.
There is no drop-out, noise, or hashing in either output signal.
The throttle position switch signals the movement and position of the throttle valve to the Engine Control Module (ECM). The switch unit is installed at the throttle housing and attached to the throttle butterfly spindle.
Throttle position switches can be configured in different ways, so it will be necessary to check manufacturer specifications for terminal and switching data. However, the general principles of operation are similar.
Inside the unit there are two sets of contacts, with each having an open or a closed state. This allows it to signal three possible throttle position states, such as:
The throttle position switch is usually a three-wire device with a 5 volts supply (12 volts on some very early systems). A typical pin configuration might be (Hella manufactured switch):
Throttle position switch faults can be both electrical and mechanical:
A faulty throttle valve switch can cause:
Selection of component related Diagnostic Trouble Codes (DTCs):
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