LED display Symptom - Possible Cause for 1985 through 1987 Honda Vehicles Note: OOOO all 4 lamps on, XXXX all 4 lamps off OOOO Engine will not start - Check for disconnected control unit ground connector. Also check for a loose connection at the ECU main relay resistor. Possible faulty ECU. OOOO Engine will not start - Check for a short circuit in the combination meter or warning light wire. Also check for a disconnected control unit ground wire. Possible faulty ECU. OOOX System does not operate - Faulty ECU OOXO System does not operate - Faulty ECU OOXX Fuel-fouled spark plugs, engine stalls frequently - Check for a disconnected MAP sensor coupler or an open circuit in the MAP sensor wire. Also faulty MAP sensor. OXOO System does not operate - Faulty ECU. OXOX Hesitation, fuel-fouled spark plugs or engine stalls frequently - Check for disconnected MAP sensor vacuum hose. OXXO High idle speed during warm-up, continued high or hard starting at low temperature - Check for disconnected coolant temperature sensor connector or an open circuit in the coolant temperature sensor wire. Also faulty Coolant Temperature sensor. OXXX Poor engine response when opening the throttle rapidly, high idle speed or engine does not rev-up when cold - Check for a disconnected throttle angle sensor connector. Also check for an open circuit in the throttle angle sensor wire. Also faulty throttle angle sensor. XOOO Engine dose not rev-up, high idle speed or erratic idling - Check for a short or open in the crank angle sensor wire. Spark plug wires interfering with the crank angle sensor wire. Also faulty crank angle sensor. XOOX Same as above (XOOO) XOXO High idle speed or erratic idling when very cold - Check for disconnected intake air temperature sensor or an open circuit in the intake air temperature sensor wire. Also faulty Intake Air Temperature sensor. XOXX Continued high idle speed - Check for a disconnected idle mixture adjuster sensor coupler or an open circuit in the idle mixture adjuster sensor wire. Also faulty Idle Mixture Adjuster sensor. XXOO System does not operate at all - Faulty ECU XXOX Poor acceleration at high altitude when cold - Check for a disconnected atmospheric pressure sensor coupler or an open circuit in the atmospheric pressure sensor wire. Also faulty Atmospheric Pressure Sensor. XXXO System does not operate at all - Faulty ECU XXXX Same as above (XXXO) CODE PROBABLE CAUSE for Honda Vehicles 1988 and later. 0 Faulty ECU (no signal) 1 Oxygen sensor or circuit. 2 Faulty ECU 3 & 5 Manifold Absolute Pressure (MAP) sensor or circuit. 4 Crank angle sensor or circuit 6 Coolant temperature sensor or circuit 7 Throttle angle sensor or circuit. 8 TDC position/crank angle sensor or circuit. 9 Crank angle sensor or circuit 10 Intake air temperature sensor or circuit. 11 No particular symptom shown or system does not operate - faulty ECU 12 Exhaust gas recirculation (EGR) failure 13 Atmospheric pressure sensor circuit. 14 Electronic air control valve (EACV) 15 No ignition output signal - possible faulty igniter. 16 Fuel injector circuit. 17 Vehicle speed sensor or circuit (VSS) 19 Lock-up control solenoid valve (automatic transmission) 20 Electronic load detector - possible open or grounded circuit in ECU wiring. 21 VTEC spool solenoid valve circuit (Civic & Del-Sol) 22 VTEC oil pressure switch circuit (Civic & Del-Sol) 23 Knock sensor (Prelude) 30 A/T control unit ECM fuel injection signal "A" (Accord & Prelude) 31 A/T control unit ECM fuel injection signal "B" (Accord & Prelude) 41 Heated oxygen sensor - heater circuit. 43 Fuel supply system circuit (except D15Z1 engine) 45 Fuel system out of range - rich or lean 48 Heated oxygen sensor circuit (D15Z1 engine) 50 Mass airflow sensor. 61 Front oxygen sensor response slow. 63 Rear oxygen sensor circuit voltage out of range. 65 Rear oxygen sensor circuit malfunction. 67 Catalyic converter efficency low. 70 Automatic Transaxle problem. 71 through 76 Cylinder misfires 80 Insufficient EGR flow 86 Engine coolant temperature sensor circuit. 92 Evaporative emission purge valve problem *Please only use this as a guide* As some are different. This should only be used as a starting point.