How do you self diagnostic a 94 ls400?

To perform a self-diagnostic on a 1994 Lexus LS400, locate the Diagnostic Test Mode (DTM) connector, typically found under the driver's side dashboard. Use a jumper wire to connect terminals TE1 and E1 in the connector. Turn the ignition to the "ON" position without starting the engine, and observe the check engine light, which will blink a series of codes indicating any issues. Refer to the vehicle's service manual for specific codes and their meanings.