Vehicle Speed Sensor (VSS) Inspection [FS5 A EL]
1. Inspect the power supply circuit for the VSS.
a. Remove the insulator from the transaxle.

b. Disconnect the VSS connector.

c. Switch the ignition to ON (engine off).
d. Measure the voltage at VSS connector terminal A (harness-side).

If there is any malfunction, repair wiring harness between VSS and AT main relay.
- VSS specification
B+
e. Switch the ignition to off.
f. Connect the VSS connector.
2. Inspect the GND circuit for the VSS.
a. Switch the ignition to off.
b. Measure the voltage at VSS connector terminal C (harness-side).

If there is any malfunction, repair wiring harness between VSS and GND.
- VSS specification
Below 1.0 V
3. Inspect the signal circuit for the VSS.
a. Connect the oscilloscope to the following TCM connector terminals and set it as below.
(+) lead: TCM terminal Z
(-) lead: battery negative terminal
Oscilloscope setting: 1 V/DIV (Y), 2 ms/DIV (X), DC range
b. Start the engine.
c. Measure the wave form when the following conditions are met.
Gear position: 3GR
Vehicle speed: 30 km/h {19 mph}

If there is any malfunction, replace the VSS..
Test yourself
A quick Mazda 3 quiz: every answer comes with an explanation and a link to the manual page.