The vehicle speed signal circuit from the electronic brake control module (EBCM) to the radio provides vehicle speed information to the radio for the purpose of raising or lowering the radio volume based on the vehicle speed. The radio increases volume as the vehicle speed increases to account for road noise. This feature is called Speed Compensated Volume (SCV)

Schematic Reference

Radio/Navigation System Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Navigation System Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Radio ON, Turn the SCV control to high, drive the vehicle at various speeds and verify that the radio maintains a comfortable listening level at different speeds.

1. Ignition OFF, disconnect the radio harness connector X4. Connect a DMM to the vehicle speed signal (VSS) circuit terminal 5 and ground.
2. Ignition ON, operate the vehicle drive wheels at 5 mph. Verify 3-7 Hertz on the VSS circuit.

⇒	If the reading is not as specified, test the VSS circuit for an open, high resistance, short to ground or short to voltage. If the circuit tests normal replace the EBCM.

3. If the circuit tests normal, replace the radio.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

See Control Module References for Radio replacement, setup, and programming