91 mazda

how can i read the codes on a 91 mazda mx6 2.2 liter with no scan tool

Take the vehicle to one of your auto supply store.

Most will scan for free.

Another way… Get a service manual. This is before OBDII. On my 90 Mazda, codes can be “read” (IIRC) by inserting a jumper in the diagnostic connector under the hood, turn the key, and count the flashes of the check engine light.

This is what the Autozone site says for your car:
"In order to retrieve the trouble code(s), you must have the Mazda system selector 49 B019 9A0 and self diagnosis checker (a digital readout tool) 49 H018 9A1 or an equivalent OBD I compliant scan tool for 1990-95."
Go by Autozone (or another chain) and see if they can read yours.