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When things go wrong your ECU stores "error codes" about the events it detected in its internal memory. Those remained stored as long as the ECU has power. The check engine light will display when an error occurs, but it won't remain on. So to check for which error codes are present in the ECU you have to put the car in test mode and then after you are all done, clear them so you can see if they reoccur.

How to check:

Open the hood and locate the diagnostic connector. Is it next to the battery and can be seen in the figure to the right. You will want to connect terminals E1 and TE1. I used a big paper clip, which I leave in the back of my car, and it is actually 'sprung' against the connector lid to add some pressure for a better connection. Clicking on the picture will give you a much better view. It might be hard to see in the picture, so the bottom figure illustrates the terminals to connect, in red, with the paper clip.

Diagnostic Block Terminals

After you do this start your car. The check engine light should now be blinking. If it is continuos quick blinking then you are fine there are no error codes, otherwise you have to count the blinks. Each set of blinks will represent one digit with a longer pause to separate digits. There may be more than one code present, but it is on a continuos loop. For example if you saw blink...blink.......blink...blink...blink...blink....... that would be a code 24. After you are done you can clear the codes by pulling the EFI fuse (15A) in the fuse block right next to the diagnostic connector for 30 seconds or more, make sure the engine is off.

Error Codes

Code	Error
11	ECU(+B)
	Diagnosis Momentary interruption in power supply to ECU. Trouble Area Ignition switch circuit Ignition switch Main relay circuit Main relay ECU
12	RPM Signal
	Diagnosis No "NE" or "G" signal to ECU within 2 seconds after engine has been cranked. Trouble Area Distributor, or CPS, circuit Distributor or CPS Starter signal circuit ECU
13	RPM Signal
	Diagnosis No "NE" signal to ECU when engine speed is about 1,000 RPM. Trouble Area Distributor, or CPS, circuit Distributor or CPS ECU
14	Ignition Signal
	Diagnosis No "IGF" signal to ECU "A" times in succession. A = 6-8 (7M-GE) A= 3 (7M-GTE) Trouble Area Igniter and ignition coil circuit Igniter and ignition coil ECU
21	Oxygen Sensor Signal
	Diagnosis Detection of oxygen sensor deterioration. Trouble Area Oxygen sensor circuit Oxygen sensor ECU
22	Water Temp Sensor Signal
	Diagnosis Open or short circuit in water temp sensor signal (THW). Trouble Area Water temp sensor circuit Water temp sensor ECU
24	Intake air Temp Sensor Signal
	Diagnosis Open or short circuit in intake air temp sensor signal (THA). Trouble Area Intake air temp sensor circuit Intake air temp sensor ECU
25	Air-Fuel Ratio Lean Malfunction
	Diagnosis When air-fuel ratio feedback compensation value or adaptive control value continues at the upper(lean) or lower(rich) limit renewed for a certain period of time. When air-fuel ration feedback compensation value or adaptive control value feedback frequency is abnormally high during feedback condition. When marked variation is detected in engine revolutions for each cylinder during idle switch on and feedback condition. Trouble Area Injector circuit Injector Fuel line pressure Air flow meter Air intake system Oxygen sensor circuit Oxygen sensor Ignition system Water temp sensor ECU
26	Air-Fuel Ratio Rich Malfunction
	Diagnosis When air-fuel ratio feedback compensation value or adaptive control value continues at the upper(lean) or lower(rich) limit renewed for a certain period of time. When air-fuel ration feedback compensation value or adaptive control value feedback frequency is abnormally high during feedback condition. When marked variation is detected in engine revolutions for each cylinder during idle switch on and feedback condition. Trouble Area Injector circuit Injector Fuel line pressure Air flow meter Cold start injector Oxygen sensor circuit Oxygen sensor Water temp sensor ECU
27	Sub-Oxygen Sensor Signal or Sensor Heater
	Diagnosis(Sub-Oxygen Sensor Signal) Open or short circuit in sub-oxygen sensor signal (OX2). Trouble Area Sub-oxygen sensor circuit Sub-oxygen sensor ECU
	Diagnosis(Sub-Oxygen Sensor Heater) Open or short circuit in sub-oxygen sensor heater (HT). Trouble Area Sub-oxygen sensor heater circuit Sub-oxygen sensor heater ECU
31	Air Flow Meter Signal
	Diagnosis (7M-GE) Open circuit in VC signal or short circuit between VS and E2 when idle contacts are closed. (7M-GTE) Open or short circuit in air flow meter signal. Trouble Area Air flow meter circuit Air flow meter ECU
32	Air Flow Meter Signal(7M-GE) HAC Sensor Signal(7M-GTE)
	Diagnosis(Air Flow Meter Signal(7M-GE)) Open circuit in E2 or short circuit between VC and VS. Trouble Area Air flow meter circuit Air flow meter ECU
	Diagnosis(HAC Sensor Signal(7M-GTE)) Open circuit or short circuit in HAC sensor signal. Trouble Area ECU
34	Turbocharger Pressure
	Diagnosis The turbocharger pressure is abnormal. Trouble Area Turbocharger Air flow meter ECU Intercooler system
41	Throttle Position Sensor Signal
	Diagnosis Open or short circuit in throttle position sensor signal. Trouble Area Throttle position sensor circuit Throttle position sensor ECU
42	Vehicle Speed Sensor Signal
	Diagnosis No "SPD" signal to ECU for 8 seconds when engine speed is between 2,500RPM and 4,500RPM (7M-GE) or 4,000RPM (7M-GTE) and coolant temp is below 80°C(176°F) and neutral start switch is off. Trouble Area Vehicle speed sensor circuit Vehicle speed sensor ECU
43	Starter Signal
	Diagnosis No "STA" signal to ECU until engine speed reaches 800RPM with vehicle not moving. Trouble Area Ignition switch circuit. Ignition switch ECU
51	Switch Signal
	Diagnosis No "IDL" signal, "NSW" signal or "A/C" signal to ECU, during diagnosis check. Trouble Area A/C switch circuit A/C switch A/C amplifier Throttle position sensor circuit Throttle position sensor ECU
52	Knock Sensor Signal
	Diagnosis Open or short circuit in knock sensor signal. Trouble Area Knock sensor circuit Knock sensor ECU
53	Knock Control Signal in ECU
	Diagnosis Knock control program faulty. Trouble Area ECU
71	EGR System Malfunction
	Diagnosis EGR gas temp below predetermined level during EGR operation. Open circuit in EGR gas temp sensor signal (THG). Trouble Area EGR system (EGR valve, EGR hose etc.) EGR gas temp sensor circuit EGR gas temp sensor VSV for EGR circuit VSV for EGR ECU

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