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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!

BE CAREFUL!

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.

IF YOUR STICKER IS GONE:

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

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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!

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ALL TESTS ARE PERFORMED W/ THE IGNITION SWITCH "ON"

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.
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Однако здесь не совсем полный перечень кодов.
Кроме того, если у тебя коробка-автомат, есть дополнительные коды
диагностики для нее.
Если с переводом траблы - обращайся, помогу.

Вот еще одно описание http://www.se-r.net/engine/ecu_codes.html
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Locate the ECU (under your dash in the center) and look for a small screw
next to a LED (towards the back end). Turn the ignition to the ON position
(engine not running). Then turn the screw fully clockwise, wait 2 seconds,
then turn it fully counter-clockwise. The LED will start to display the
code by a series of long flashes, followed by a series of short flashes.
Your check engine light on the instrument cluster will also flash in the
same sequence. This sequence will repeat.

Trouble codes Circuit or system
(long flashes, short flashes)
1,1 Crank angle sensor/circuit
1,2 Mass airflow sensor/circuit
1,3 Coolant temp sensor
1,4 Vehicle speed sensor
2,1 Ignition signal
3,1 ECM control unit
3,2 EGR function
3,3 Oxygen sensor
3,4 Knock sensor
3,5 Exhaust gas temp sensor
4,3 TPS - Throttle position sensor
4,5 Injector leak
5,5 (NORMAL SYSTEM OPERATION)

Once the screw is turned fully clockwise and counter-clockwise again, the
ECU will be reset. This is from the Haynes manual for 91-94 Sentras (both
1.6 and 2.0).
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И еще http://www.se-r.net/faq/ecu.html. Вот оно:
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TOOLS REQUIRED TO ACCESS ECU ON A 200SX SE-R:

Philips screwdriver (to remove screws on cover)
10 mm socket (to remove 2 nuts holding down both the cover and ECU)
Ratcheting socket driver
Short extension
Universal joint

HOW TO SWITCH TEST MODES:

Remove screws and nuts holding cover down. Take care not to drop in to area
behind console, 200SX"s are known to eat little nuts and screws, etc, in
that area (at least mine does...). Remove cover from ECU, the cover is a
little tight around the ECU... don"t be afraid to pull hard on it, it won"t
break.
Turn ignition switch to "ON". Do not start engine
Diagnostic Test Mode I - BULB CHECK
Start Engine.
Diagnostic Test Mode I - MALFUNCTION WARNING
Turn diagnostic test mode selector on ECM fully clockwise.
Wait at least 2 seconds
Turn diagnostic test mode selector on ECM fully counter clockwise.
Diagnostic Test Mode II - SELF-DIAGNOSTIC RESULTS
Start Engine
Diagnostic Test Mode II - FRONT HEATED OXYGEN SENSOR MONITOR
Turn diagnostic test mode selector on ECM fully clockwise. (Note, This step
erases the DTC/MIL, if not, turn test mode selector fully clockwise and
repeat step.)
Wait at least 2 seconds
Turn diagnostic test mode selector on ECM fully counter clockwise.
Return to Step 2.

NOTES...

In Diagnostic Test Mode II - SELF-DIAGNOSTIC RESULTS (Step 6) the ECU will
flash the current DTC on the MIL (malfunction indicator lamp). eg MIL 12
(for Mass Air Flow Sensor) flashes long-pause-short-short-pause, and
repeats. MIL 43 flashes long-long-long-long-pause-short-short-short-pause,
and repeats.
In Diagnostic Test Mode II - FRONT HEATED OXYGEN SENSOR MONITOR, the MIL
acts as a primitive Air/Fuel Ratio meter. In closed loop (cruising, light
acceleration): ON = LEAN, and OFF = RICH, in open loop (idling, heavy
throttle, lift throttle) the light keeps the condition that the light had
just before entering open loop.
Switching modes is not possible when the engine is running.
When ignition switch is turned of during diagnosis, power to the ECM will
drop after approx. 1 second and the diagnosis will automatically return to
Daignostic Test Mode I.
Turn back diagnostic test mode select to the fully counter clockwise
position whenever vehicle is in use.

DIAGNOSTIC TROUBLE CODES (DTCS):

CONSULT MIL*1 Items
P0000 55 No self diagnostic failure indicated
P0100 12 Mass Air Flow Sen
P0110 41 Int Air Temp Sen
P0115 13 Coolant Temp Sen
P0120 43 Throttle Posi Sen
P0125 98 Coolant Temp Sen
P0130 37 Closed Loop
P0130 33 Front O2 Sensor
P0135 91 FR O2 Sen Heater
P0136 77 Rear O2 Sensor
P0170 76 Fuel Inj System
P0300 71 Random Misfire
P0301 68 Cyl 1 Misfire
P0302 67 Cyl 2 Misfire
P0303 66 Cyl 3 Misfire
P0304 65 Cyl 4 Misfire
P0325 34 Knock Sensor
P0335 82 Crank Pos Sen (OBD)
P0340 11 Camshaft Posi Sen
P0400 32 EGR System
P0402 36 EGRC-BPT Valve
P0420 72 TW Catalyst System
P0500 14 Vehicle Speed Sen
P0505 25 IACV-AAC Valve
P0605 31 ECM
P0705 103 Park/Neut Posi SW
P1320 21 Ign Signal-Primary
P1336 95 Crank P/S (OBD) Cog
P1400 105 EGRC Solenoid/V
P1401 35 EGR Temp Sensor
P1605 84 A/T Diag Comm Line
P1900 28 Over Heat

Automatic Transmission codes:

CONSULT MIL*1 Items
P0705 111 Inhibitor Switch
P0710 128 Fluid Temp Sensor
P0720 112 Vhcl Speed Sen A/T
P0725 127 Engine Speed Sig
P0731 113 A/T 1st Signal
P0732 114 A/T 2nd Signal
P0733 115 A/T 3rd Signal
P0734 116 A/T 4th Signal
P0740 124 Tor Conv Clutch Sv
P0745 125 Line Pressure S/V
P0750 118 Shift Solenoid/V A
P0755 121 Shift Solenoid/V B
P1705 126 Thrtl Posi Sen A/T
P1760 123 Overrun Clutch S/V
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