How to Read Malfunction Codes for Your DOHC 240SX

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.

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.

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).

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.

* 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...

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!

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 =

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

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.

* 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.)

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