How do you check for flash codes without a scan tool?

If your vehicle is 1995 or later, you must use an OBDII scanner to retrieve the trouble codes. Fortunately, there are auto parts stores that will scan free of charge. If your vehicle is pre-1995, you can try your local public library to see if there is a repair manual (Haynes or Chilton) for your vehicle available for checkout. In the manual you will find full instructions on how to retrieve the codes without a scanner and what each code means.