MAKING SENSE OF ECU CODES (Honda Cars) My Check-Engine light came on while I was on a cross-country road trip. With just 2 girls with practically no knowledge about cars, it sure scared the hell out of us, especially when it happened at a God-forsaken place like South Dakota! This guide will help you understand a little better about your car and when such an incident happens, you know exactly what is wrong, and how much danger you and your car may be, so that you can decide to stay or go on. (Text by Stace)

What are ECU problem codes?

ECU problems codes are diagnostic outputs from the ECU, used to indicate in what area a problem lies. Usually the check engine warning light comes on for a serious problem, but will not necessarily come on for a minor problem. The ECU will remember problem codes even with the ignition off; and the only way to clear the codes is to disconnect the battery or remove the hazard fuse for half a minute or so.

How to read ECU codes?

Find the diagnostic connector, which is a two wire blue connector found near the passengers feet, or in the centre console (Each car may differ. Image below is for Civic Si). Short out the diagnostic connector with a piece of wire, e.g. a paper clip bent to a U-shape, or hair pin. To read the codes, turn the ignition on.

Click to view for instructions

The check engine light on the dash will flash the problem codes. If there are more than 1 problem, a different code will subsequently follow the first after a brief pause.

There are two types of flashes - short and long, which are combined to represent number codes. Each short flash indicates 1 unit and each long flash represents 10 units. Problem codes 1 - 9 are indicated by 1 - 9 flashes, problem codes 10 - 90 use 1 - 9 long flashes. If the code is more than 9, the long flashes will start first before the short ones. The codes will continue to repeat as long as your ignition is on.

Code	Area	Meaning
1	Oxygen Sensor "A" (Primary)	defective circuit or unplugged / defective sensor
2	Oxygen Sensor "B"	defective circuit or unplugged / defective sensor
3	MAP Sensor (Manifold Absolute Pressure)	defective circuit or unplugged / defective sensor
4	CKP Sensor (Crankshaft Position Sensor)	defective circuit or unplugged / defective sensor
5	MAP Sensor (Manifold Absolute Pressure)	mechanical problem / disconnected piping
6	ECT Sensor (Engine Coolant Temperature)	defective circuit or unplugged / defective sensor
7	TP Sensor (Throttle Position)	defective circuit or unplugged / defective sensor
8	TDC Sensor (Top Dead Center)	defective circuit or unplugged / defective sensor
9	CYP Sensor (Cylinder)	defective circuit or unplugged / defective sensor
10	IAT Sensor (Intake Air Temperature)	defective circuit or unplugged / defective sensor
12	EGR Lift Sensor (Exhaust Gas Recirculation)	defective circuit or unplugged / defective sensor
13	BARO Sensor (Atmospheric Pressure)	defective circuit or unplugged / defective sensor
14	IAC Valve (Idle Air Control)	defective circuit or unplugged / defective sensor
15	Ignition Output Signal	missing or defective ignition output signal
16	Fuel Injector System	defective circuit or unplugged / defective fuel injector
17	VSS (Vehicle Speed Sensor)	defective circuit or unplugged / defective sensor
19	Automatic Transmission Lock Up Control Solenoid Valve	defective circuit or unplugged / defective solenoid valve
20	Electrical Load Detector	defective circuit or unplugged / defective sensor
21	VTEC Solenoid Valve	defective circuit or unplugged / defective solenoid valve
22	VTEC Oil Pressure Switch	defective circuit or unplugged / defective oil pressure switch
23	KS (Knock Sensor)	defective circuit or unplugged / defective sensor
30	Automatic Transmission Signal: "A" / SEAF / SEFA / TMA or TMB	defective circuit or unplugged / defective sensor
31	Automatic Transmission Signal "B"	defective circuit or unplugged / defective sensor
41	Primary Oxygen Sensor - Heater	circuit malfunction
43	Fuel Supply System	defective or malfunctioning fuel supply system
45	System Too Lean or Too Rich	malfunction in the fuel monitoring systems
48	LAF Sensor (Lean Air Fuel)	defective circuit or unplugged / defective sensor
54	CKF Sensor (Crankshaft Speed Fluctuation)	defective circuit or unplugged / defective sensor
58	TDC Sensor 2 (Top Dead Center)	defective circuit or unplugged / defective sensor
61	Oxygen Sensor, Heated - Sensor 1 (Primary)	high voltage, low voltage, or slow response
63	Oxygen Sensor, Heated - Sensor 2 (Secondary)	high voltage, low voltage, or slow response
65	Oxygen Sensor Heater (Secondary)	malfunctioning or defective oxygen sensor heater
67	Catalyst system Efficiency Below Threshold	malfunctioning or defective catalyst system
70	Automatic Transmission	malfunction with the automatic transmission controls
71	Cylinder 1 Misfire or a Random Misfire	a condition is present that is creating a cylinder misfire
72	Cylinder 2 Misfire or a Random Misfire	a condition is present that is creating a cylinder misfire
73	Cylinder 3 Misfire or a Random Misfire	a condition is present that is creating a cylinder misfire
74	Cylinder 4 Misfire or a Random Misfire	a condition is present that is creating a cylinder misfire
75	Cylinder 5 Misfire or a Random Misfire	a condition is present that is creating a cylinder misfire
76	Cylinder 6 Misfire or a Random Misfire	a condition is present that is creating a cylinder misfire
80	Exhaust Gas Recirculation	insufficient flow detected
76	ECT Sensor (Engine Coolant Temperature)	circuit range / performance problem
90	Evaporative Emission Control System	leak detected in the fuel tank area
91	Fuel Tank Pressure Sensor	low input
92	Evaporative Emission Control System	insufficient purge flow