Vc output circuit

The ecm constantly generates 5 v power from the battery voltages supplied to the +b (batt) terminal to operate the microprocessor. The ecm also provides this power to the sensors through the vc output circuit.

When the vc circuit is short-circuited, the microprocessor in the ecm and sensors that are supplied with power through the vc circuit are inactivated because the power is not supplied from the vc circuit. Under this condition, the system does not start up and the mil does not illuminate even if the system malfunctions.

Under normal conditions, the mil is illuminated for several seconds when the ignition switch is first turned on. The mil goes off when the engine is started.

1. 1
   Check mil
2. 2
   Check that the malfunction indicator lamp (mil) lights up when turning the ignition switch on.

1. 1
   Check communication between intelligent tester and ecm
2. 2
   Connect the intelligent tester to the dlc3.
3. 3
   Turn the ignition switch on and tester on.
4. 4
   Check the communication between the tester and ecm.

   

1. 1
   Check mil (throttle position sensor)
2. 2
   Disconnect the b3 throttle body connector.
3. 3
   Turn the ignition switch on.
4. 4
   Check the mil.

   

4. Reconnect the throttle body connector.

1. 1
   Check mil (accelerator pedal position sensor)
2. 2
   Disconnect the a4 accelerator pedal position sensor connector.
3. 3
   Turn the ignition switch on.
4. 4
   Check the mil.

   

4. Reconnect the accelerator pedal position sensor connector.

5. Check mil (canister pump module)

1. 1
   Disconnect the s3 canister pump module connector.
2. 2
   Turn the ignition switch on.
3. 3
   Check the mil.

   

4. Reconnect the canister pump module connector.

1. 1
   Check mil (battery current sensor)
2. 2
   Disconnect the b29 battery current sensor connector.
3. 3
   Turn the ignition switch on.
4. 4
   Check the mil.

   

1. Reconnect the battery current sensor connector.

1. 1
   Check harness and connector
2. 2
   Disconnect the b3 throttle body connector.
3. 3
   Disconnect the a4 accelerator pedal position sensor connector.
4. 4
   Disconnect the s3 canister pump module connector.
5. 5
   Disconnect the b29 battery current sensor connector.
6. 6
   Disconnect the a9 and b30 ecm connectors.
7. 7
   Measure the resistance.

Standard resistance (check for short)

1. 1
   Reconnect the throttle body connector.
2. 2
   Reconnect the accelerator pedal position sensor connector.
3. 3
   Reconnect the canister pump module connector.
4. 4
   Reconnect the battery current sensor connector.
5. 5
   Reconnect the ecm connectors.