With Manufacturer's Scan Tool

When the PCM senses an abnormality in the input or output systems, the D4 indicator light in the gauge assembly will blink. When the 16P Data Link Connector (DLC) (located under the dash on the driver's side) is connected to the OBD II Scan Tool or Honda PGM Tester as shown, the scan tool or tester will indicate the Diagnostic Trouble Code (DTC) when the ignition switch is turned ON.
When the D4 indicator light has been reported on, connect the OBD II Scan Tool conforming to SAE J1978 or Honda PGM Tester to the DLC (16P). Turn the ignition switch ON, and observe the DTC on the screen of the OBD II Scan Tool or Honda PGM Tester. After determining the DTC, refer to Diagnosis by Symptom. Symptom Related Diagnostic Procedures

NOTE: See the OBD II Scan Tool or Honda PGM Tester user's manual for specific instruction.