Sfi System - Variable Resistor Circuit

Brand:

Toyota

Model Name:

Yaris NCP90 91 92 93

Manual:

Repair Manual

Section:

2Nz-Fe Engine Control System

Title:

Sfi System

  1. Description

  2. Wiring diagram

  3. Inspection procedure

  4. Check co/hc

  5. Adjust idling co concentration

  6. Inspect variable resistor

  7. Inspect ecm (vc voltage)

  8. Check harness and connector (variable resistor - ecm)

SFI SYSTEM > Variable Resistor Circuit


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DESCRIPTION

The variable resistor is used to adjust the concentration of CO in the exhaust during idling. By turning the idle mixture adjusting screw, located on the variable resistor, clockwise, the contact inside the resistor is moved and the voltage at the VAF terminal rises accordingly. Conversely, turning the adjusting screw counterclockwise reduces the VAF terminal voltage. When the VAF terminal voltage rises, the ECM increases the fuel injection volume slightly, thus making the air-fuel ratio slightly richer.

WIRING DIAGRAM


Sfi System - Cranking Holding Function Circuit Yaris


INSPECTION PROCEDURE

HINT:
Always use a CO meter when adjusting the concentration of CO during idling. If a CO meter is not available, do not attempt to adjust the idling CO concentration.
1.CHECK CO/HC
  1. Ensure the following:All the vacuum lines are properly connected.The CO meter is properly calibrated. Yaris

  2. Ensure the following:

    1. All the vacuum lines are properly connected.

    2. The CO meter is properly calibrated.

  1. Start the engine.

  1. Ensure the following:

    1. The parking brake is securely applied.

    2. The transmission gear is in neutral.

    3. All the accessories are switched off.

  1. Warm up the engine and check that the idling speed is appropriate.

  1. Race the engine at 2,500 rpm for about 2 minutes.

  1. Insert a tester probe at least 40 cm (1.3 ft) into the tailpipe.

  1. Measure the CO concentration 1 to 3 minutes after racing the engine to allow the concentration to stabilize.

Standard CO concentration rate at idling:
1.0 to 2.0 %
HINT:
If the result is outside the standard range shown above, maintain the measurement conditions obtained during this procedure. The measurement conditions are used in the CO concentration adjustment procedure described below.


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PROCEED TO NEXT CIRCUIT INSPECTION SHOWN IN PROBLEM SYMPTOMS TABLE
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2.ADJUST IDLING CO CONCENTRATION
  1. Ensure all the conditions prepared in the measurement procedure. Yaris

  2. Ensure all the conditions prepared in the measurement procedure.

  1. Regulate the idling CO concentration so that it is within 1.0 to 2.0 %.

    HINT:
    Use SST and the idle mixture adjusting screw located on the C37 variable resistor. By turning the adjusting screw, the idling CO concentration rate can be regulated.
    Reference:
    Result
    		Proceed To
    Unable to obtain standard concentration rate
    		A
    Standard concentration rate obtained
    		B


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ADJUSTMENT COMPLETE
A
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3.INSPECT VARIABLE RESISTOR
  1. Remove the C37 variable resistor. Yaris

  2. Remove the C37 variable resistor.

  1. Measure the resistance between terminals 1 and 2 of the variable resistor.

    Standard resistance:
    Tester Connections
    		Specified Conditions
    E2 (1) - VC (2)
    		3.5 to 6.5 kΩ

  1. Measure the resistance between terminals 1 and 3 when the idle mixture adjusting screw is turned fully clockwise and fully counterclockwise.

    Standard resistance:
    Tester Connections
    		Adjusting Screw
    		Specified Conditions
    E2 (1) - VAF (3)
    		Turned fully clockwise
    		3.5 to 6.5 kΩ
    Turned fully counterclockwise
    		0 kΩ
HINT:
When the adjusting screw is turned fully clockwise, the resistance is the same as the measurement value between terminals 1 and 2. When the adjusting screw is turned fully counterclockwise, the resistance changes to 0 kΩ.

  1. Reinstall the variable resistor.



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REPLACE VARIABLE RESISTOR
OK
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4.INSPECT ECM (VC VOLTAGE)
  1. Disconnect the C37 variable resistor connector. Yaris

  2. Disconnect the C37 variable resistor connector.

  1. Turn the ignition switch to ON.

  1. Measure the voltage between the terminals of the variable resistor connector.

    Standard voltage:
    Tester Connections
    		Specified Conditions
    E2 (C37-1) - VC (C37-2)
    		4.5 to 5.5 V

  1. Reconnect the variable resistor connector.



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REPLACE ECM (Click here)
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5.CHECK HARNESS AND CONNECTOR (VARIABLE RESISTOR - ECM)
  1. Disconnect the C37 variable resistor connector. Yaris

  2. Disconnect the C37 variable resistor connector.

  1. Disconnect the C20 ECM connector.

  1. Check the resistance.

    Standard resistance (Check for open):
    Tester Connections
    		Specified Conditions
    E2 (C37-1) - EVAF (C20-87)
    		Below 1 Ω
    VC (C37-2) - VC (C20-117)
    VAF (C37-3) - VAF (C20-64)
    Standard resistance (Check for short):
    Tester Connections
    		Specified Conditions
    E2 (C37-1) or EVAF (C20-87) - Body ground
    		10 kΩ or higher
    VC (C37-2) or VC (C20-117) - Body ground
    VAF (C37-3) or VAF (C20-64) - Body ground

  1. Reconnect the variable resistor connector.

  1. Reconnect the ECM connector.



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REPAIR OR REPLACE HARNESS OR CONNECTOR
OK
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REPLACE ECM (Click here)