AT 261 - Chapter 9 - Electronic Engine Control Systems



AT 261 - Chapter 21 TP Sensors

Name: _________________________________________________

Date: _______________________________________________________

Station 1 - POSITION SENSOR CIRCUIT

Many electronically controlled systems require that a component’s position be monitored throughout its entire field of travel. One such application of this is in the electronic temperature control system where the control module needs to monitor the travel of the throttle. In this case, the module needs continuous feedback on the component’s position. This information is provided by a variable resistance position sensing circuit.

Like the temperature sensor circuit, the position sensor circuit contains a control module, sensor, wiring and connectors The control module has a voltage regulator, limiting resistor and a DC voltmeter function.

Although the position sensor is a variable resistor, it operates differently than the temperature sensor. The resistance of the position sensor changes mechanically. The position sensor contains a movable arm, or wiper, that slides across a fixed resistor. The wiper is mechanically connected to the component that requires monitoring. As the position of the component changes, the resistance of the position sensor changes. By using the voltmeter function, the control module determines the position of the component by the voltage at the wiper.

This circuit is also a voltage divider circuit, but unlike the temperature sensor circuit, it monitors voltage at the sensor by a sensor return line (M).

Although the temperature sensor and position sensor circuits are both voltage divider circuits, the total resistance of the position sensor circuit does not vary, therefore calculating the signal voltage is slightly different.

During normal operation, as the position being sensed moves to one end of its travel, the resistance of the position sensor will either increase or decreases depending on circuit design. The control module uses the monitored voltage as an input to determine what type of changes should be made in the system. If the resistance increases, the monitored voltage at the wiper will increase. The reverse is true as the sensor resistance decreases, the monitored voltage decreases. This circuit produces an analog voltage signal normally ranging from zero to five volts.

During excessively high or low resistance conditions, the circuit cannot give an accurate representation of the position that it is designed to sense. Any resistance value that is not within the circuit design limits will cause an inaccurate input. An open anywhere in either the reference voltage (VREF) or signal line will cause a zero volt reading. The same is true if there is an open in the sensor itself, or it the open is on the VREF side of the wiper. If the open is either in the sensor on the ground side of the wiper, or in the ground line, the module will sense five volts. A short-to-ground in either the reference line or signal line will also cause a zero volt level for monitored voltage. If the ground line to the module grounds prematurely, the input will not be affected.

NORMAL OPERATION:

Resistance Measurement - Locate the symbol shows a resistor with an arrow. It is labeled 10K. (See Page 2)

How many terminals does the potentiometer have? ___________________

Measure the resistance across the outer two terminals. __________________

( Turn the potentiometer knob all the way clockwise and measure the resistance across the center terminal (3) (signal) and the bottom terminal (1) (ground).

What resistance do you measure? ___________________

( Begin to turn the knob (wiper) counter-clockwise and make the following measurements:

Knob Position Resistance

¼ Travel __________________

½ Travel __________________

¾ Travel __________________

Full Travel __________________

Complete the following statement:

A change in the knob (wiper) ______________, causes a change in the resistance measured at the wiper.

Voltage Measurements Build the circuit shown below.

What is the constant voltage supplied to this sensor? ____________________

( Turn the potentiometer knob all the way clockwise and measure the voltage at point M.

The voltmeter symbol indicates the point where the computer “MONITORS” the potentiometer signal.

What voltage do you measure? __________________________

( Begin to turn the knob (wiper) counter-clockwise and make the following measurements:

Knob Position Voltage at M

¼ Travel ______________________ V ½ Travel ______________________ V

¾ Travel ______________________ V Full Travel ______________________ V

Complete the following statement:

A change in the knob (wiper) position causes a change in the _________________ measured at the wiper.

Does the potentiometer produce an ANALOG signal (varying BETWEEN 0 and 5 volts) or a DIGITAL signal (switched, 0 OR 5 volts)?

___________________________________________________________________________

ABNORMAL OPERATION:

These exercises introduce faults into the circuit in order to observe the change in normal operation and to identify the fault.

Open Ground:

( Monitor the voltage at point M in the circuit.

( Adjust the knob until you get a reading of about 2.5 volts, which represents a TPS ½ throttle voltage.

( REMOVE the ground to the potentiometer at point 1.

|This lab was partially constructed|

|using text, and graphics from the |

|following source; |

|Model 1835 |

|Advanced Electricity/Electronics |

|Instructor Guide |

|ATech Training, Inc. |

|12290 Chandler Drive • P.O. Box |

|297 |

|Walton, KY 41094 USA |

|Phone: (859) 485-7229 • Fax: (859)|

|485-7299 |

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|Website: |

What voltage do you measure at point M? ___________________________

REPLACE the ground at point 1.

Open Reference:

( REMOVE the reference voltage at point 2, in the circuit.

What voltage do you measure at point M? ____________________________

REPLACE the reference at point 2.

Open Signal:

( REMOVE the signal wire at point 3, in the circuit.

What voltage do you measure at point M? __________________________

( REPLACE the signal at point 3.

Short Signal:

( SHORT point 3 to ground with an additional wire.

What voltage do you measure at point M? ___________________________

( REMOVE the short at point 3.

( Complete the following table to summarize your results:

Fault Voltage at M

Open Ground ___________________ V

Open Reference _________________ V

Open Signal ____________________ V

Short Signal ________________ V

QUESTIONS FROM YOUR BOOK - Page 347

Name six uses for the TP sensor.

___________________________________________________________________________________________________

___________________________________________________________________________________________________

Station 2 – On Car Testing.

Vehicles – 2003 Ford Mustang

2003 Ford ZX2

Tools DVOM, Packprobe Pins, Job Aid - Wire Diagram:

Locate the Throttle Position Sensor:

Locate which wires are:

Power (5v) (reference) - Wire Color _______________________________________

TP Input to PCM - Wire Color _______________________________________

Sensor Ground (Signal Return) - Wire Color _______________________________________

Using a scan tool, (Generic OBDII is fine)

Turn vehicle on, but do not start the vehicle.

( What is the reading for the TP sensor ___________________________%. (Norm.)

( Depress the throttle to WOT

( What is the reading for the TP sensor @ WOT ___________________________ %

( Disconnect the TP sensor

( Now, what is the reading with the TP sensor disconnected ___________________________%. (Disc.)

( Reconnect the TP sensor

Turn off the vehicle.

Back probe power and sensor ground wires.

Turn on the vehicle, but do not start it.

Record your voltage ________________________________ V

(Your reading should read almost exactly 5 volts).

Move the pin from the +5v (sensor power) to the sensor return

Record your voltage ________________________________ V

Slowly depress the throttle to WOT.

Does it match the graph on the job aid? __________________________

Is this TP sensor functional? __________________________

If needed, access the car’s recorded codes and clear them with the scan tool.

Job Aid for ZX2/Mustang Lab (Station 2)

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