Driveability & Emissions Controls

ELECTRONIC ENGINE CONTROLS

Throttle Position (TP) Sensor

Fig. 1: Throttle position sensor attached to the side of the throttle body assembly-Impreza

This sensor sends the ECU an output signal which corresponds to the opening of the throttle valve. Using this output signal, the ECU precisely controls the air/fuel ratio during acceleration, deceleration and idling. The TP sensor and the throttle switch are combined as part of an assembly. The switch signal turns ON only when the throttle is opened to the idle position or at Wide Open Throttle (WOT) acceleration.

Idle Contact

1. Using an ohmmeter, check that continuity exists between terminals A and C when the throttle is fully closed and that no continuity exists when the throttle is opened.
2. Insert a feeler gauge (thickness gauge) of 0.0217 in. (0.55mm) between the stopper screw on the throttle chamber and the stopper (this corresponds to the throttle opening of 1.5 degrees). Ensure that continuity exists between terminals A and C.
3. Insert a feeler gauge (thickness gauge) of 0.0362 in. (0.92mm) between the stopper screw on throttle chamber and the stopper (this corresponds to a throttle opening of 2.5 degrees). Ensure that continuity exists between terminals A and C.

1. Disconnect the TP sensor harness.
2. Measure the resistance with an ohmmeter between terminals 2 and 3.
   1. With the throttle fully closed, the resistance should be 12 kilo-ohms.
   2. With the throttle fully opened, the resistance should be 5 kilo-ohms.
3. The resistance should change smoothly as the throttle plates are moved open and closed.
4. If the TP sensor checks out satisfactorily, check the TP sensor harness for continuity and ground path.
5. Check the idle switch by disconnecting it from the ECU harness.
6. Connect an ohmmeter between terminals 1 and 2.
   1. With the throttle fully closed, the idle switch should be 0 ohms.
   2. With the throttle fully opened, the idle switch resistance should be 1 mega-ohm or more.
      

Throttle Opening Signal

1. Unplug the throttle sensor and measure the resistance between terminals 1 and 2.
2. The resistance should be 6-18 kilo-ohms. Replace the sensor if the resistance measurement is out of range.
3. Measure the resistance between terminals 1 and 3. It should be:
   • 5.8-17.8 kilo-ohms with the throttle closed
   • 1.5-5.1 kilo-ohms with the throttle open
4. The resistance must change smoothly through its entire range. If the resistances are either out of range or the resistance change is not smooth, replace the throttle sensor.

Fig. 2: Disconnect the wire harness from the throttle position sensor-Legacy

Fig. 3: Paint a matchmark on the sensor and throttle body for ease of installation and adjustment

Fig. 4: Remove the sensor retainer screws

Fig. 5: Lift off the throttle position sensor

1. Disconnect the negative battery cable.
2. Disconnect the throttle sensor electrical harness.
3. Place a matchmark on the throttle position sensor and throttle body mounting surface, so that during installation, the sensor can be properly aligned.
4. Remove the 2 screws securing the throttle sensor to the throttle body assembly.
5. Remove the throttle sensor by pulling it in the axial direction of the throttle shaft.
6. Remove the throttle sensor O-ring and discard.

To install:

7. Using a new throttle O-ring, install the throttle sensor, aligning the matchmarks. Install and hand-tighten the retainer screw.
8. Connect the throttle sensor electrical harness.
9. Connect the negative battery cable.

END OF SECTION