CAS Testing


The CAS contains two transistors that are controlled either magnetically or
optically by two spinning arms. These transistors switch the inputs of the engine computer.
The inputs inside the computer are connected to a 5 bolt power suppply through resistors. When a transistor is turned on, the signal switched to 0 volts. Otherwise, it stays at 5 volts.

Wiring Check

Disconnect the CAS connector and check for voltages on the plug.

The CAS connector is by the dipstick on a 1.8 engine. On a 1.6 engine, it's on the other side of the valve cover.


If you don't know how to use a voltmeter, you should not be doing this.

With the connector oriented like this (tab up), the normal measurement is 0 volts, +12 volts, +5 volts, +5 volts. As shown, the black wire in the harness with be at the left

Also check the first pin (black wire) for continuity to ground

If the voltages and ground connection check out, the wire harness to the computer is good.

Electrical Test - per shop manual  

The factory shop manual shows the above method for testing the CAS. Hook up power and ground. Then you need a load resistor and a 5 volt supply. With a volt meter hooked up to the resistor, you will read either 0 or +5 volts, depending on the position of the CAS rotor.

The SGC pin should switch between +5 and 0 volts twice per revolution.
The SGT pin should switch between +5 and 0 volts four times per revolution.


Disclaimer: Not a certifed auto mechanic. Not a Mazda technician. The information on this page is my own interpretation and may be flat-ass wrong. Use at your own discretion.