ECU diagnostic mode explained

[gtst lad]

The ECU is in the passenger footwell, behind the plastic kickplate to the left of your feet. You'll have to remove the computer from the mounts in the footwell, as the led/leds you'll need to see are pointing towards the front of the car. Switch on the ignition but don't start engine, the led on the ECU will begin glowing turn the selector screw clockwise all the way.

There's three types of factory ecu in Skylines, One type has two LEDs and five modes, the other type has one LED and two modes and the last type has no LEDs, the output is done with the engine check light in the instrument cluster.

For two led ecus the led will flash once, pause, flash twice, pause... all the way up to five this is the diagnostic mode Mode 1 = one flash, mode 5 = five flashes. When you reach the right mode, turn the screw back counter-clockwise. Mode 3 is what most people use.

For one led ecus wait a couple of seconds, and turn the screw back counter-clockwise, the ECU is now in mode 2 the engine check light on the dash will mirror the LED on the computer.

The led will flash out a code or series of codes if there is more than one fault More recent ECU's have two LED's red is first digit, green is second digit, eg red 2x flash, green 1x flash = code 21. The ecus on most R32's have one LED, long flash = first digit, short flash = second digit, eg long, long, short = code 21.

Codes:
11 - Crank Angle Sensor/Camshaft Position Sensor
12 - Air Flow Meter
13 - Engine Coolant Temperature Sensor
14 - Vehicle Speed Sensor
21 - Ignition Signal
22 - Fuel Pump
23 - Idle Switch
24 - Throttle Valve Switch
25 - Idle Speed Control Valve
26 - Boost Pressure Sensor
27 -
28 - Cooling Fan Circuit
29 -
30 -
31 - ECM
32 - EGR Function
33 - Heated Oxygen Sensor
34 - Knock Sensor
35 - Exhaust Gas Temperature Sensor
36 - EGR Control-Back Pressure Transducer
37 - Knock Sensor
38 - Right hand bank Closed Loop (B2)
41 - Intake Air Temperature Sensor
42 - Fuel Temperature Sensor
43 - Throttle Position Sensor
45 - Injector Leak
47 - Crankshaft Position Sensor
51 - Injector Circuit
53 - Oxygen Sensor
54 - A/T Control
55 - No Malfunction
63 - No. 6 Cylinder Misfire
64 - No. 5 Cylinder Misfire
65 - No. 4 Cylinder Misfire
66 - No. 3 Cylinder Misfire
67 - No. 2 Cylinder Misfire
68 - No. 1 Cylinder Misfire
71 - Random Misfire
72 - TWC Function right hand bank
76 - Fuel Injection System Function right hand bank
77 - Rear Heated Oxygen Sensor Circuit
82 - Crankshaft Position Sensor
84 - Automatic Transmission Diagnostic Communication Line
87 - Canister Control Solenoid Valve Circuit
91 - Front Heated Oxygen Sensor Heater Circuit right hand bank
94 - TCC Solenoid Valve
95 - Crank Position Cog
98 - Engine Coolant Temperature Sensor
101 - Front Heated Oxygen Sensor Heater Circuit right hand bank
103 - Park/Neutral Position Switch Circuit
105 - EGR and EGR Canister Control Solenoid Valve Circuit
108 - Canister Purge Control Valve Circuit
111 - Inhibitor Switch
112 - Automatic Transmission Speed Sensor
113 - Automatic Transmission 1st Signal
114 - Automatic Transmission 2nd Signal
115 - Automatic Transmission 3rd Signal
116 - Automatic Transmission 4th Signal
118 - Automatic Transmission Shift Solenoid Valve A
121 - Automatic Transmission Shift Solenoid Valve B
123 - Automatic Transmission Overrun Clutch Solenoid Valve
124 - Automatic Transmission TOR Conv Solenoid Valve
125 - Automatic Transmission Line Pressure Solenoid
126 - Automatic Transmission Throttle Position Sensor
127 - Automatic Transmission Engine Speed Signal
128 - Automatic Transmission Fluid Temperature Sensor

Turn the ignition off to put the ECU back to normal.

[Squeak]

Real Time O2 sensor test procedure
Do the same procedure as above to get the ECU into mode 2 (single LED ECU)
or for mode 1 (dual LED ECU's)

1 Start the engine.

2 Warm the engine, and then run under no load at 2000 rpm for
the test.

3a Single LEDs: on = lean, off = rich

3b Dual LED's: green LED on = lean, green LED off = rich

4 Go by the trend shown, e.g. mostly on = lean, mostly off = rich.

The LED should be flashing between 5-10 times per 10 seconds
under normal conditions.