14
Identifying the Terminals of an Unknown Throttle Position Sensor
This is a procedure for identifying the correct terminal connections of
any potentiometer-style throttle position sensor (almost all three-terminal
TP sensors). A DVOM or analog Ohmmeter is required.
1.
Set the meter to resistance mode and set it to a scale that can read up
to 10K or 20K Ohms (if it is not auto-ranging). Please keep in mind when
setting up and reading the meter that "K" means thousands of Ohms. In
other words, 15K Ohms is the same as 15,000 Ohms.
2.
Connect the meter to two pins at a time while operating the lever or cam
of the TPS. Watch the meter while rotating the sensor. Check all three
pairs of pins until you find a pair that does not change resistance when
you rotate the sensor. The two pins that do not change resistance are
the fixed ends of the resistance element (+5V and ground). The
remaining pin that did change is known as the "wiper". It is the moving
contact that slides along the resistance element to give the varying
voltage. This is the output or signal terminal of the sensor and should be
connected to the green wire (Vehicle pin 3).
3.
Next, with the sensor at the idle or closed throttle position, measure the
resistance between the wiper (output) and each of the end terminals (the
two whose resistance did not change in step 2) of the sensor. The end
terminal with the lowest resistance to the wiper (at idle) is the ground
terminal, and should connect to the black
, “TPS GROUND” wire of the
controller (Vehicle pin 16). The terminal with the higher resistance to the
wiper is the 5 volt reference input to the sensor and should connect to
the orange wire (Vehicle pin 11) in the harness.
General Guidelines for setting up Throttle Position Sensors
The linkage to a throttle position sensor should use most of the
rotating range of the throttle position sensor. This can be adjusted by
changing the ratio of the linkage. Also, please make sure that a small
amount of the sensor's travel is being used at idle. You will want a TPS
voltage of at least 0.35 volts at idle, never zero. This is done to allow the
controller to detect problems with the TP sensor. For instance, if the sensor
becomes disconnected or the linkage falls off, the TPS voltage will fall
below the set idle threshold. If the TPS voltage goes below the idle
threshold, the controller assumes that the TPS is bad and will switch to
failsafe line pressure and default shift points. This is done to prevent
damage to the transmission from low line pressure and will provide a safe
"limp home" mode.
