1985-1995 EFI engines do not require a "scanner" to read CEL (Check Engine Light) error codes.
The ECM also does not trigger the CEL every time an error code is set.
Trouble Codes (CEL) on vehicles made before 1996 use the OBD-I (On Board Diagnostics) system, while 1996+ vehicles use the OBD-II system which requires a "scanner" to obtain to obtain the error codes.
All you need is a metal paper clip or small piece of wire. Insert one end each of the paper clip etc. (called the jumper) into the terminals labeled TE1 and E1 in the diagnostic check connector, found under the hood next to the fuse box. Then, you turn the ignition key to on and the CEL will blink in a specific sequence. By counting the blinks, you determine what code you have. First it will blink the first digit of the code. Then there will be a 1.5 second pause, and the second digit of the code will blink. If you had another code, there would be a 2.5 second pause between them and the process would repeat. Then, once all codes have been flashed, there will be a 4.5 second pause, and then the entire series will start over from the beginning. For example, if _ represents a pause and * represents a blink, code 12 and code 42 would look like this if they cycled around twice:
*_**_ _****_**_ _ _ _*_**_ _****_**
Here is a link to the procedure to check the codes manually, as well as the basic generic code descriptions.