E N G L I S H
83
Exhaust Gas Recirculation Valve Position Sensor (EVP)
and Vane Air Flow Meter (VAF), etc.
An analog Throttle Position Sensor (TPS) is found on
many vehicles. The TPS informs the vehicle computer
of the followings:
- Throttle opening,
- Whether and How fast throttle is opening,
- Whether and How fast throttle is closing,
- When the throttle is wide open,
- When the throttle is at idle.
One of its most important functions is to tell the
computer that the throttle is opening. It replaces
the accelerator pump found on carbureted engines,
preventing the engine from stumbling when the
throttle is opened quickly. When that happens,
manifold absolute pressure (MAP) quickly rises
(vacuum drops) causing vaporized gasoline to
condense on the manifold walls. Since there is less fuel
available to the cylinders, more fuel must be added to
the air stream.
Another important function is to tell the computer
that the throttle is closing.
To maintain acceptable emissions, the computer must
lean out the mixture when MAP drops (vacuum rises).
For best fuel economy, the computer completely shuts
off fuel in some engines when vacuum is high and
throttle is at idle. Therefore, the computer must know
when the throttle is at idle.
Throttle position information is a variable resistance
from a potentiometer attached to the throttle shaft.
Wide-Open throttle signal and closed-throttle signal
come from switches attached to the TPS.
The TPS is really just a potentiometer or variable
resistor. As you sweep the throttle, the resistance
changes. As its resistance changes, so does the voltage
signal returning to the computer. The TPS can be
tested either by watching the voltage change or by
watching the resistance change, using the analog
pointer on the Meter.
Resistance Change Test
The check resistance change:
- Connect jumper wires between the connector and
the sensor.
- Set the rotary switch to resistance (Ω).
Connect:
- Black test probe to the Ground circuit.
- Red test probe to the signal line. (Refer to the
manufacturer’s schematic).
Set:
- RECORD (MAX-MIN-AVG) function on the Meter.
Rotate the TPS by moving the throttle and watch
the bar graph move as the TPS turns: The resistance
reading should change as the signal arm on the TPS is
moved (signal sweep).
As you rotate the TPS to change resistance, the bar
graph moves smoothly if the TPS is good and moves
erratically if it is bad.
Summary of Contents for UD88
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