Memorized vs. Non-Memorized Codes
WARNING: This page is about a different car, the 1994 Mazda MX-3. However, it is still accessible from the selected car via links, so may be relevant.
Some sensor or circuit failures are stored in ECU and are known as memorized codes. While other circuit failures, called non-memorized codes, are not stored. Non-memorized codes can be retrieved if ignition is not turned off before accessing codes.
NOTE:
To access non-memorized trouble codes, DO NOT stop engine. Connect jumper wire across self-diagnostic connector terminals TEN and GND. Observe MIL and note trouble codes.