Plug a BNC test lead into Channel A on the PicoScope, place a black clip on the test lead with the black moulding (negative) and a Back-pinning Probe onto the test lead with the coloured moulding (positive). Clip the black clip onto the battery negative terminal and probe the throttle switch with the Back-pinning Probe (see note below). Plug a BNC test lead into Channel B on the PicoScope and a Back-pinning Probe onto the test lead with the coloured moulding (positive). Probe the throttle pedal switch with the other Back-pinning Probe as illustrated in Figure 1 (see note below). If you cannot reach the terminal or plug with a probe, then you may be able to use a breakout lead or box if you have one available.
Note: the switch will have three wires normally consisting of:
Check the technical data for the system to be tested.
Figure 1 shows the two connections made in order to dual trace the switched contacts within the throttle switch.
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.
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.
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.
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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