GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Throttle Position Sensor (TPS)

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OPERATION



See Figure 1

The TPS is mounted to the throttle body, opposite the throttle lever and is connected to the throttle shaft. Its function is to sense the current throttle valve position and relay that information to the ECM. Throttle position information allows the ECM to generate the required injector control signals. The TPS consists of a potentiometer which alters the flow of voltage according to the position of a wiper on the variable resistor windings, in proportion to the movement of the throttle shaft. As throttle angle is changed (the accelerator is pressed down), the output of the sensor changes.



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Fig. Fig. 1: The throttle position sensor is mounted on the throttle body-3.3L engine

At closed throttle, the output of the sensor is fairly low (0.5 V). As the throttle opens, the output voltage should rise towards 5V. By monitoring the sensor output voltage, the control module can determine fuel delivery based on throttle angle.

TESTING



TPS Output Check Test

See Figures 2, 3 and 4

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Fig. Fig. 2: The TPS is located on the side of the throttle body



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Fig. Fig. 3: Inspect the voltage of the TPS when the linkage is closed, then ....



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Fig. Fig. 4: ... check for change when the TPS linkage is at WOT

  1. Disconnect the TPS harness from the TPS.
  2.  
  3. Using suitable jumper wires, connect a digital voltmeter to terminals A and B on the TPS.
  4.  
  5. With the ignition ON and the engine running, the TPS voltage should be 0.450-1.25 volts at base idle to approximately 4.5 volts at wide open throttle.
  6.  
  7. If the reading on the TPS is out of specification, replace it.
  8.  
  9. Turn ignition OFF , remove jumper wires, then reconnect harness to throttle position switch.
  10.  

REMOVAL & INSTALLATION



Except Multi-Port Injection

See Figure 5

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Fig. Fig. 5: Throttle position sensor mounting

This TP sensor is not adjustable and is not supplied with attaching screw retainers. Since these TPS configurations can be mounted interchangeably, be sure to order the correct one for your engine with the identical part number of the one being replaced.

  1. Disconnect the negative battery cable.
  2.  
  3. If necessary, remove the air cleaner assembly along with the necessary duct work.
  4.  
  5. Detach the TP electrical connector.
  6.  
  7. Unfasten the TP sensor attaching screws. If the sensor is riveted to the throttle body, it will be necessary to drill out the rivets.
  8.  
  9. Remove the TP sensor from the throttle body assembly.
  10.  

The throttle position sensor is an electrical component and should not be immersed in any type of liquid solvent or cleaner, as damage may result.

To install:
  1. With the throttle valve closed, install the TP sensor onto the throttle shaft. Rotate the TPS counterclockwise to align the mounting holes.
  2.  
  3. Apply Loctite 262 or equivalent to the retaining screws. Install the retaining screws or rivets, then tighten the screws to 18 inch lbs. (2 Nm).
  4.  
  5. Attach the sensor electrical connector.
  6.  
  7. Install the air cleaner assembly, then connect the negative battery cable.
  8.  

Multi-Port Injection

See Figure 6

The 3.0 and 3.3L engines are equipped with adjustable TP sensors.

  1. Disconnect the negative battery cable.
  2.  
  3. If necessary for access to the sensor, remove the air cleaner tube resonator assembly.
  4.  
  5. Detach the electrical connector from the TP sensor.
  6.  
  7. Unfasten the attaching screws, lock washers and retainers, as applicable.
  8.  
  9. Remove the throttle position sensor. If necessary, remove the screw holding the actuator to the end of the throttle shaft.
  10.  



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Fig. Fig. 6: View of the Throttle Position (TP) sensor mounting-3.0L engine shown

To install:
  1. With the throttle valve in the normal closed idle position, install the TP sensor on the throttle body assembly, making sure the sensor pickup lever is located above the tang on the throttle actuator lever.
  2.  
  3. Install the retainers, screws and lock washers using a thread locking compound. Tighten to 18 inch lbs. (2 Nm).
  4.  
  5. Attach the sensor electrical connector.
  6.  
  7. If removed, install the air cleaner tube resonator assembly.
  8.  
  9. Connect the negative battery cable.
  10.  

ADJUSTMENT



3.0L and 3.3L Engines
  1. Install three jumper wires between the TP sensor and the harness connector or use a "SCAN" tool and view throttle position
  2.  
  3. With the ignition in the ON position and the throttle closed, use a digital voltmeter connected between "A" and "B"', adjust the position of the throttle sensor to obtain a reading of 0.50-0.59 volts for a 3.0L engine and 0.38-0.42 volts for a 3.3L engine.
  4.  
  5. Tighten the screws to 18 inch lbs. (2.0 Nm), recheck the reading to make sure the adjustment has not changed.
  6.  
  7. With the ignition OFF , remove the jumper wires, then connect the harness to the TP sensor.
  8.  

 
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