AIR CONDITIONING SYSTEM (for Automatic Air Conditioning System) > Vehicle Speed Signal Circuit

for Preparation Click here


DESCRIPTION

The air conditioning amplifier assembly monitors signals from the speedometer sensor via the combination meter assembly. The air conditioning amplifier assembly uses these signals to adjust the thermistor signal.

WIRING DIAGRAM


E225335E04


INSPECTION PROCEDURE

HINT:
Check that the speedometer in the combination meter assembly operates normally before inspecting the vehicle speed signal circuit (Click here).
1.CHECK AIR CONDITIONING AMPLIFIER ASSEMBLY


    E170958E08

  1. Remove the air conditioning amplifier assembly with its connectors still connected (Click here).

  1. Using an oscilloscope, check the waveform of the air conditioning amplifier assembly.

    Measurement Condition 
    Item
    		Content
    Tester Connection
    		A38-9 (SPD) - Body ground
    Tool Setting
    		5 V/DIV., 20 ms./DIV.
    Condition
    		Driving at approximately 20 km/h (12 mph)

    OK:
    Waveform is as shown in the illustration.
    Text in Illustration 
    *a
    		Component with harness connected
    (Air Conditioning Amplifier Assembly)

    HINT:
    As the vehicle speed increases, the wavelength becomes shorter.


NG
Go to step 2
OK

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE (Click here)  

2.CHECK COMBINATION METER ASSEMBLY


    E224591E06

  1. Remove the combination meter assembly with its connector still connected (Click here).

  1. Connect an oscilloscope to the combination meter assembly connector.

  1. Check the waveform.

    Measurement Condition 
    Item
    		Content
    Tester Connection
    		C27-6 - Body ground
    Tool setting
    		5 V/DIV., 20 ms./DIV.
    Condition
    		Vehicle is driven at approximately 20 km/h (12 mph)

    OK:
    Waveform is as shown in the illustration.
    Text in Illustration 
    *a
    		Component with harness connected
    (Combination Meter Assembly)

    HINT:
    When the system is functioning normally, one wheel revolution generates 4 pulses. As the vehicle speed increases, the width indicated by (A) in the illustration narrows.


NG
REPLACE COMBINATION METER ASSEMBLY (Click here)
OK


3.CHECK HARNESS AND CONNECTOR (COMBINATION METER - AIR CONDITIONING AMPLIFIER)

  1. Disconnect the C27 combination meter assembly connector.

  1. Disconnect the A38 air conditioning amplifier assembly connector.

  1. Measure the resistance according to the value(s) in the table below.

    Standard Resistance:
    Tester Connection
    		Condition
    		Specified Condition
    C27-6 - A38-9 (SPD)
    		Always
    		Below 1 Ω
    A38-9 (SPD) - Body ground
    		Always
    		10 kΩ or higher


NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

REPLACE AIR CONDITIONING AMPLIFIER ASSEMBLY (Click here)