HOLDEN GEN III V8, Service Training

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GEN III V8 ENGINE MANAGEMENT
THROTTLE POSITION SENSOR
The Throttle Position (TP) sensor is connected to
the throttle shaft on the throttle body unit. It is a
potentiometer with one end connected to 5 volts
from the PCM and the other end to PCM earth. A
third wire connects from a sliding contact in the TP
sensor to the PCM allowing the PCM to measure
the voltage from the TP sensor. As the throttle is
moved (accelerator pedal moved), the output of the
TP sensor changes. At a closed throttle position,
the output of the TP sensor is below 1.25V. As the
throttle valve opens, the output increases so that,
at wide-open throttle (WOT), the output voltage
should be about 4 volts.
By monitoring the output voltage from the TP
sensor, the PCM can determine fuel delivery based
on throttle valve angle (driver demand). A broken
or loose TP sensor can cause intermittent bursts of
fuel from the injectors, and an unstable idle,
because the PCM interprets the throttle is moving.
The TP sensor is not adjustable and there is no set
value for voltage at closed throttle because the
actual voltage at closed throttle can vary from
vehicle to vehicle due to tolerances. The PCM has
a special program built into it that can adjust for the
tolerances in the TP sensor voltage reading at idle.
The PCM uses the reading at closed throttle idle
for the zero reading (0% throttle) so no adjustment
is necessary. Even if the TP sensor voltage
reading was to be changed by: tampering, throttle
body coking, sticking cable or any other reason,
the TP sensor will still be 0%. The PCM will learn
what the closed throttle value is every time the
throttle comes back to closed throttle.
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