95 - 98 240sx ECU Codes  - comp Rich Bjornson -  

Items DTC Ref. Page
Camshaft Position Sensor 11 EC-88
Mass Air Flow Sensor 12 EC-92
Coolant Temperature Sensor 13 EC-97
Vehicle Speed Sensor 14 EC-101
Ignition Signal Primary 21 EC-105
IACV-AAC Valve 25 EC-110
ECM 31 EC-115
EGR System 32 EC-117
Front O2 Sensor 33 EC-125
Knock Sensor 34 EC-130
EGR Temp Sensor 35 EC-133
EGRC-BPT Valve 36 EC-137
Closed Loop 37 EC-139
Intake Air Temp Sensor 41 EC-140
Throttle Position Sensor 43 EC-145
CYL 4 Misfire 65 EC-150
CYL 3 Misfire 66 EC-150
CYL 2 Misfire 67 EC-150
CYL 1 Misfire 68 EC-150
Random Misfire 71 EC-150
TW Catylist System 72 EC-154
Fuel Injection System 76 EC-157
Rear O2 Sensor 77 EC-162
Crank Position Sensor (OBD) 82 EC-167
A/T Diag Comm Line 84 EC-171
Crank P/S (OBD) Cog 95 EC-174
Coolant Temperature Sensor 98 EC-178
Park/Neutral Position Switch 103 EC-183
EGRC Solenoid/V 105 EC-188
Inhibitor Switch 111 AT
Vehicle Speed Sensor A/T 112 AT
A/T 1st Signal 113 AT
A/T 2nd Signal 114 AT
A/T 3rd Signal 115 AT
A/T 4th Signal or TCC 116 AT
Shift Solenoid/V A 118 AT
Shift Solenoid/V B 121 AT
Overrun Clutch S/V 123 AT
TOR Conv clutch SV 124 AT
Line Pressure S/V 125 AT
Throttle Position Sensor A/T 126 AT
Engine Speed Signal 127 AT
Fluid Temp Sensor 128 AT
A/T Comm Line XX EC-192

Many thanks to Richard Lestage who posted his version for the SOHC!
We've used his format for the DOHC and thank him for his efforts!!

We suggest that you read this in it's entirety before rolling up your sleeves and doing this procedure. It may seem a bit complicated at first, but when you understand how the ECU stores and displays the Malfunction Codes, you will find that the process is pretty simple and easy to do.

Only a screw driver is required to read the trouble codes stored in the ECU (Electronic Control Unit). The following instructions allow you to easily read and erase the Malfunction Code on your beloved's ECU.

These instructions come from the 1991- 16 Valve Factory Service Manual.

Reading the codes requires accessing the ECU and placing the unit in one of two self diagnostic modes using a small flat head screw driver. The codes are displayed by a single RED L.E.D. in the ECU and the Check Engine Light.

1. Accessing to the ECU

The ECU is located at the right of the right side footwell. The "side" is determined as you sit in the car facing forward. (For cars in North America, the right side would be the passenger side)

You need to remove 2- "rivet" type fasteners of the right doorstep in order to get the kick panel out. To remove the plastic fasteners, unscrew the center part and pull out the other part. 2- metal screws and another "rivet" type fastener hold the kick panel.

Under the panel, is the ECU with its connector. Unfortunately, you have to access to the side of the ECU that is against the firewall. Remove the two screws at the top and bottom of the ECU and gently turn it to get to the Model Selector and RED L.E.D. Don't unplug the ECU to do this!


There should be a small sticker by the Mode Selector that tells you to turn it clockwise to set the Modes and to be sure to return it all the way counter-clockwise to the original position when the car is in use. You will also see the RED L.E.D. inside the ECU.


Mark the original position of the Mode Selector. This is a VERY IMPORTANT position for the Mode Selector! (This should be fully counter-clockwise).

2. The Diagnostic Modes


There are 2- Modes and 2- Conditions for the Engine to be in for running diagnostics:

All Modes are with the Ignition Switch in the ON position
Mode I (Engine OFF)- Bulb Check
Mode I (Engine ON) - Malfunction Warning
Mode II (Engine OFF)- Stored Self Diagnostic Results
Mode II (Engine ON)- Exhaust Gas Sensor Monitor

Note: The ECU will automatically return to Mode I when the ignition is switched OFF. When the ECU is changed from Mode II back to Mode I by using the Mode Selector, the malfunction code(s) stored for Mode II will be erased. More on this later.

3. Changing Modes

Note: Switching Modes is not possible when the engine is running.

* Turn the Ignition Switch ON.
* The ECU is now in Mode I.
* To switch to Mode II:

Turn the ECU Mode Selector fully CLOCKWISE, hold for at least 2-seconds and then return the Mode Selector to it's original position. You are now in Mode II.

* Return to Mode I by turning the Mode Selector fully CLOCKWISE again, holding for another 2-seconds and turning it back to the original position.

Note: Doing this will ERASE any Malfunction Codes that are stored in the ECU for Mode II.

Example: If you found a Malfunction Code of 34 when you very first switched to Mode II and then cycled back to Mode I, then again to Mode II, you'll get a 55 (everything's OK) code. This is assuming that you didn't start the car between changing modes. When you start the engine, any current malfunction codes will be store by the ECU until you erase them or they get dumped.

Malfunction Codes are stored by the ECU for 50 times of cranking the starter. Then they are erased. If the same conditions are present, the Malfunction Code will be stored again for 50 cranks of the starter. And so on...

4. Reading the Malfunction Codes:

The Malfunction Codes are indicated by the number of flashes by the RED L.E.D. and the Check Engine Light. You can read either one. They flash the same information. For example, when the RED L.E.D. flashes once and after a short pause flashes twice, this signifies the number "12".

Note: If you find that your looking at a RED L.E.D. and a GREEN L.E.D., you've got a different ECU than is described here. See the FAQ on this same page that was written by Richard Lestage for the SOHC ECU!



Mode I (Engine OFF)- Bulb Check:

In this Mode, the RED L.E.D. in the ECU and the Check Engine Light stay ON. If either remain OFF, check the bulb.

Mode I (Engine ON) - Malfunction Warning:
RED L.E.D. is OFF = OK
RED L.E.D. flashes =

For California Models Only:

Code # Description

12 Air flow meter circuit
13 Engine temperature sensor circuit
14 Vehicle speed sensor circuit
31 E.C.U. (E.C.C.S. control unit)
32 EGR function
33 Exhaust gas O2 sensor circuit
35 Exhaust gas temperature circuit
43 Throttle position sensor circuit
45 Injector leak

For Non-California Models:

RED L.E.D. ON = The ECU's CPU or the Crank Angle sensor is malfunctioning.


Mode II (Engine OFF)- Stored Self Diagnostic Results

Code # Description

11 + Crank angle sensor circuit
12 E Air flow meter circuit
13 E Engine temperature sensor circuit
14 E Vehicle speed sensor circuit
21 + Ignition signal circuit
31 E E.C.U. (E.C.C.S. control unit)
32 * E EGR function
33 E Exhaust gas O2 sensor circuit
34 Detonation sensor circuit
35 * E Exhaust gas temperature circuit
43 E Throttle position sensor circuit
45 * E Injector leak
54 Signal circuit from A/T control unit to ECU (A/T only)
55 No malfunction in the above circuits

* = California models only
E = Check Engine light will show this code.
+ = Check items causing a malfunction of the crank angle sensor 1st, if both #11 and #21 are displayed at the same time.

Mode II (Engine ON)- Exhaust Gas Sensor Monitor

* Warm up the engine and see that the Temperature Gauge is in it's usual position.

* Run the engine at about 2,000 RPM for about 2- minutes under no-load conditions.

* Make sure the RED L.E.D. or the Check Engine Light goes ON and OFF more than 5- times every 10- seconds; measured at 2,000 RPM under no-load. (This is easiest to do while sitting in the driver's seat and watching the Check Engine Light.)

After the diagnostic, Turn the ignition 'off' to return to mode I.


This may seem quite complicated, but if we can figure it out, you'll have no problems!


'91 s13