With OBD II Scantool/Honda PGM Tester

When the TCM 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 passenger 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 confirming to SAE J1978 or Honda PGM Tester to the DLC (16P) behind the ashtray. 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.

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

Some PGM-FI problems will also make the (D4) indicator light come on After repairing the PGM-FI system, disconnect the BACK UP fuse (7.5 A) in the under-hood fuse/relay box for more than 10 seconds to reset the TCM memory, then recheck.

NOTE: Disconnecting the BACK UP fuse also cancels the radio anti-theft code, preset stations and the clock setting. Get the customer's code number, and make note of the radio presets before removing the fuse so you can reset them.