Toyota Tacoma (2015-2018) Service Manual: Vehicle Speed Signal Circuit between Radio Receiver and Combination Meter

Toyota Tacoma (2015-2018) Service Manual / Audio / Video / Audio And Visual System / Vehicle Speed Signal Circuit between Radio Receiver and Combination Meter

DESCRIPTION

for Audio Function:

The radio and display receiver assembly receives a vehicle speed signal from the combination meter assembly and sends the signal to radio and display receiver assembly.

for Automatic Sound Levelizer (ASL):

This circuit is necessary for the Automatic Sound Levelizer (ASL) built into the radio and display receiver assembly.
The Automatic Sound Levelizer (ASL) function automatically adjusts the audio system volume level in order to compensate for increased vehicle noise (vehicle noise tends to increase as vehicle speed increases). The ASL adjusts the volume level based upon vehicle speed signals that it receives from the combination meter assembly.

for "Bluetooth":

Vehicle speed signals are received from the combination meter assembly and used to cancel "Bluetooth" function operation.
The radio and display receiver assembly recognizes that the vehicle is being to driven and makes it impossible to connect or register a "Bluetooth" device while driving.

HINT:

A voltage of 12 V or 5 V is output from each ECU and then input to the combination meter assembly. The signal is changed to a pulse signal at the transistor in the combination meter assembly. Each ECU controls the respective system based on the pulse signal.
If a short occurs in any of the ECUs or in the wire harness connected to an ECU, related components will not operate normally.

WIRING DIAGRAM

PROCEDURE

1.	CHECK VEHICLE SIGNAL (OPERATION CHECK)

(a) Enter the "Vehicle Signal Check Mode" screen. Refer to Check Vehicle Signal Check Mode in Operation Check (See page ).

(b) While driving the vehicle, compare the "SPEED" indicator to the reading on the speedometer. Check if these readings are almost equal.

HINT:

The combination meter assembly receives the vehicle speed signal from the skid control ECU via CAN communication. Therefore, perform the following inspection referring to values on the Data List of the skid control ECU because it is the source of the vehicle speed signal.

OK:

Vehicle speed displayed on the "Vehicle Signal Check Mode" screen is almost the same as the actual vehicle speed measured using the Techstream.

for Hydraulic Brake Booster Type (See page )
for Vacuum Brake Booster Type (See page )

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE

2.	INSPECT COMBINATION METER ASSEMBLY (OUTPUT WAVEFORM)

(a) Check the output waveform.

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

(2) Connect an oscilloscope to terminal C9-40 (+S) and body ground.

(3) Turn the ignition switch to ON.

(4) Turn a wheel slowly.

(5) Check the signal waveform according to the condition(s) in the table below.

Item	Condition
Measurement terminal	C9-40 (+S) - Body ground
Tool setting	5 V/DIV., 20 ms./DIV.
Vehicle condition	Wheel being rotated

OK:

The waveform is similar to that shown in the illustration.

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.

Text in Illustration

*a	Component with harness connected (Combination Meter Assembly)

GO TO METER / GAUGE SYSTEM

3.	CHECK HARNESS AND CONNECTOR (RADIO AND DISPLAY RECEIVER ASSEMBLY - COMBINATION METER ASSEMBLY)

(a) Disconnect the R31 radio and display receiver assembly connector.

(b) Disconnect the C9 combination meter assembly connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
R31-17 (SPD) - C9-40 (+S)	Always	Below 1 Ω

REPLACE RADIO AND DISPLAY RECEIVER ASSEMBLY

REPAIR OR REPLACE HARNESS OR CONNECTOR

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