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Nissan ECU Trouble Codes - Reading, resetting, etc...

I found this at, but I cleaned up the code list to better fit the 240SX and added the diagnostic instructions...

When your check engine light goes on, it is because you engine senses a problem with one of its many sensors and wants to let you know of the problem. When this happens, you should pull the ECU (located behind the plastic shield on the right hand side of the passenger side foot-well), run the diagnostic test (instructions below), read the code, and fix the problem (replace the sensor or whatever).

Once you’ve pulled the ECU and located the ‘mode selector’ screw on the side...

Turn the ignition switch to the on position, but do not start the engine. All of the 'dummy' lights in the dash should be on.

Turn the 'diagnostic mode selector' screw on the side of the ECU fully clockwise. The check engine light will go out. Now wait at least 2 seconds, and then turn the screw back to its original position (fully counter clockwise).

The check engine light will then begin to flash the trouble code -

The number of long flashes is the 1st digit, and the number of short flashes is the 2nd digit...

So for example, a code 45 would be:

blink........blink........blink........blink - (short pause) - blink...blink...blink...blink...blink

If there is only one code, it will flash over and over and over...

If there is more than one code, it will flash the first, then the second, and so on...then just keep repeating the codes (in numerical order) over and over and over

Now you have 2 options:

To clear all stored codes and turn off the check engine light, turn the ‘mode selector’ screw fully clockwise. Wait at least 2 seconds, then turn the screw all the way back counter clockwise. Then start the car...

To keep the codes stored, simply turn the key off as the check engine light is flashing and the ECU will keep all stored codes and the check engine light will remain on.

COMPUTER CODES for Nissan Vehicles:

Probable 'trouble code' cause for Nissan vehicles 1984 and later...

11 - Camshaft position sensor

12 - Mass Air Flow Meter Sensor

13 - Coolant Temperature sensor circuit

14 - Vehicle Speed Sensor signal circuit is open

15 - Mixture ratio is too lean despite feedback control; fuel injector clogged

21 - Ignition signal in the primary circuit is not being entered to the ECU during cranking or tuning

22 - Idle speed control valve or circuit

23 - Idle switch (throttle valve switch) signal circuit open

24 - Park/Neutral switch malfunctioning

25 - Idle Air Control Valve

28 - Cooling fan

29 - Fuel system rich

31 - ECU internal problem

32 - EGR malfunction (California models)

33 - Front O2 sensor

34 - Detonation (Knock) Sensor

35 - Exhaust Gas Temperature sensor (California models)

36 - EGRC-BPT valve

37 - Closed Loop

41 - Intake Air temperature sensor

43 - Throttle Position Sensor

44 - No trouble codes stored in ECU

45 - Injector fuel leak (California models only)

51 - Fuel injector circuit open (California models only)

53 - Oxygen sensor (300ZX right side)

54 - Short between automatic transmission control unit (TCU) and ECU

55 - Normal engine management system operation is indicated – this means all is OK.

65 - Misfire detected - cylinder no. 4

66 - Misfire detected - cylinder no. 3

67 - Misfire detected - cylinder no. 2

68 - Misfire detected - cylinder no. 1

71 - Misfire Detected - Random

72 - Catalytic Converter Malfunction

74 - EVAP pressure sensor

75 - EVAP leak

76 - Fuel injection system

77 - Rear O2 sensor

81 - Vacuum cut bypass valve

82 - Crankshaft Position Sensor

84 - Automatic Tranny-to-Fuel Injection Communication Line

85 - VTC solenoid

87 - EVAP canister purge control

91 - Front oxygen sensor

95 - Crank Cog

98 - Coolant temperature sensor

103 - Park/neutral switch

105 - EGR and canister control valve (Solenoid)

108 - EVAP volume control

111 - Inhibitor Switch

112 - Vehicle Speed Sensor A/T

113 - A/T 1st Signal

114 - A/T 2nd Signal

115 - A/T 3rd Signal

116 - A/T 4th Signal or TCC

118 - Shift Solenoid/V A

121 - Shift Solenoid/V B

123 - Overrun Clutch S/V

124 - TOR Converter Clutch SV

125 - Line Pressure S/V

126 - Throttle Position Sensor A/T

127 - Engine Speed Signal

128 - Fluid Temp Sensor


Use this as a guide, not a Bible - These codes are assumed current through 1997.

If codes other than the ones listed are indicated, repeat the diagnostic test...

If you fix the problem and the same code reappears repeatedly, substitute an ECU that is known to be good and repeat the diagnostic test.

Also, another set of instructions can be found at under the FAQ section.

I hope this helps you diagnose your ECU problems...if you find any inaccuracies or have any more useful info, please e-mail me -

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