Description of On-Board Diagnostics

In the event of a PGM-FI system electrical malfunction, a dash mounted indicator lamp will light and stay lit. If the dash warning lamp is on, or if a system malfunction is suspected even though the lamp is off, it is necessary to check the electronic control unit LED display. The LED display is on the ECU, and the indicator lamps operate whenever the ignition is on and a trouble code is stored in the ECU memory.
On Civic, CRX and 1985 Accord, the ECU contains four LED's, numbered 1, 2, 4 an 8 when counted from right to left. When the warning lamp on the dash is lit and a failure code is stored in the ECU memory, the LED indicators will be illuminated to indicate the failure code.
On 1986-88 Accord and Prelude a single LED is used. When an abnormality is detected the LED display on the ECU blinks. The LED blinks a certain number of times, with the number of blinks indicating the number of the failure code. After the LED blinks a number of times there will be a 2 second pause and the LED will blink out the number of the next failure code.
System diagnosis requires the use of a suitable digital multimeter and system checker harness 07999-PD6000A. The harness checker allows test connections to be made at the ECU, while leaving the main harness connectors connected.
To diagnose system malfunctions on Civic, CRX and 1985 Accord, start with preliminary self-diagnosis chart. If problem cannot be resolved using the preliminary self-diagnosis chart, proceed to self-diagnosis charts. Read through charts noting bold faced type and locate chart that most closely describes the symptom and/or operation of warning lamp and LEDs. Follow tests exactly and repair any malfunctions found before proceeding to next step. After completing diagnosis and repairs, clear self-diagnosis codes by disconnecting the battery ground cable for at least 10 seconds. After connecting the cable, check to see that the LED display is turned off.
To diagnose system malfunctions on 1986 Accord and 1986-87 Prelude, start with preliminary chart. If problem can not be resolved using the preliminary self-diagnosis chart, proceed to self-diagnosis chart for 1986-88 Accord and 1986-87 Prelude models. Read through charts noting bold faced type and locate chart that most closely describes the symptom and/or operation of warning lamp and LED's. Follow tests exactly and repair any malfunctions found before proceeding to next step. After completing diagnosis and repairs, clear self-diagnosis codes from memory by disconnecting the battery ground cable for at least 10 seconds. After connecting the cable, check to see that the LED display is turned off.