With Manufacturer's Scan Tool

When the [D4] indicator light has been reported on, connect the OBD II Scan Tool (conforming to SAE J19781 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 Trouble Code Descriptions. Diagnostic Trouble Code Descriptions

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