VC Output Circuit

2AZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: VC Output Circuit

VC Output Circuit

DESCRIPTION

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.
HINT: 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.

WIRING DIAGRAM





INSPECTION PROCEDURE

PROCEDURE

1. CHECK MIL
(a) Check that the Malfunction Indicator Lamp (MIL) lights up when turning the ignition switch ON.
OK:
MIL lights up
OK -- SYSTEM OK
NG -- Continue to next step.
2. CHECK COMMUNICATION BETWEEN TECHSTREAM AND ECM
(a) Connect Techstream to the DLC3.
(b) Turn the ignition switch ON and tester ON.
(c) Check the communication between the tester and ECM.
Result:






A -- GO TO MIL CIRCUIT
B -- Continue to next step.
3. CHECK MIL (THROTTLE POSITION SENSOR)
(a) Disconnect the B3 throttle body connector.
(b) Turn the ignition switch ON.
(c) Check the MIL.
Result:





(d) Reconnect the throttle body connector.
A -- REPLACE THROTTLE BODY ASSEMBLY
B -- Continue to next step.
4. CHECK MIL (ACCELERATOR PEDAL POSITION SENSOR)
(a) Disconnect the A4 accelerator pedal position sensor connector.
(b) Turn the ignition switch ON.
(c) Check the MIL.
Result:





(d) Reconnect the accelerator pedal position sensor connector.
A -- REPLACE ACCELERATOR PEDAL POSITION SENSOR
B -- Continue to next step.
5. CHECK MIL (CANISTER PUMP MODULE)





(a) Disconnect the S3 canister pump module connector.
(b) Turn the ignition switch ON.
(c) Check the MIL.
Result:





(d) Reconnect the canister pump module connector.
A -- REPLACE CHARCOAL CANISTER ASSEMBLY
B -- Continue to next step.
6. CHECK MIL (BATTERY CURRENT SENSOR)
(a) Disconnect the B29 battery current sensor connector.
(b) Turn the ignition switch ON.
(c) Check the MIL.
Result:





(d) Reconnect the battery current sensor connector.
A -- REPLACE BATTERY CURRENT SENSOR
B -- Continue to next step.
7. CHECK HARNESS AND CONNECTOR
(a) Disconnect the B3 throttle body connector.
(b) Disconnect the A4 accelerator pedal position sensor connector.
(c) Disconnect the S3 canister pump module connector.
(d) Disconnect the B29 battery current sensor connector.





(e) Disconnect the A9 and B30 ECM connectors.
(f) Measure the resistance.
Standard resistance (check for short):





(g) Reconnect the throttle body connector.
(h) Reconnect the accelerator pedal position sensor connector.
(i) Reconnect the canister pump module connector.
(j) Reconnect the battery current sensor connector.
(k) Reconnect the ECM connectors.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE ECM