240SX ECU Error Codes – Reading and Resetting

Rather than taking your 240SX to Nissan and letting them charge $90 to pull the codes from your ECU and tell you what needs to be replaced, You can read the codes and reset the ECU yourself in 15 minutes. This page contains instructions how to reset the ECU and the 240SX ECU Codes list.

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).

How to Reset 240SX ECU and Read the Codes

Located the ‘mode selector’ screw on the side once you’ve pulled the ECU. 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 reset the 240sx ECU error codes. The number of long flashes is the 1st digit, and the number of short flashes is the 2nd digit.

So for example, a 240SX ECU codes is 45, would be:
blink …….. blink …….. blink …….. blink – (short pause) – blink … blink … blink … blink … blink.

If there is only one 240SX ECU 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 engine.

To keep the 240sx ECU 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.

240SX ECU Codes List

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

Disclaimers

Use this 240SX ECU codes as a guide, not a Bible. These codes are assumed current through 1997. Another set of instructions can be found at 240SX.org under the FAQ section.

If the 240SX ECU 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.

I hope this helps you diagnose your 240SX ECU problems. If you find any inaccuracies or have any more useful info related to 240SX ECU codes, please drop your comment below.