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Extracting Diagnosis Codes from the Engine ECU

1995 Mitsubishi FTO GPX

October 2002

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The FTO's engine ECU monitors everything from sensors to injectors, solenoid valves to ignition. If it notices a problem, it records this in the form of a diagnostic code. A Mitsubishi dealer equipped with the right MUT-II diagnostic setup is apparently capable of accessing these codes.

But what if no such service is available to you? The FTO Workshop manuals do not provide any alternative method for extracting diagnostic codes.

Fortunately, the EVO Workshop manuals show a much easier way! Although the codes differ from the FTO, the method of extraction is identical... and the whole process requires nothing more than a single electrical lead...

Disclaimer: Do not attempt any wiring modifications yourself without (a) checking the connections, wire colours, etc. on your own vehicle, and (b) knowing what you are doing. I take no responsibility for any cooked wiring, ECUs or anything else you may feel like playing with. Any work done on your own vehicle is done so at your own risk...

The first step is to remove the panel underneath the steering wheel. This simply requires the removal of four screws. Note that the bonnet release cable and lever will still be connected to this panel - just drop the panel down and keep it out of the way.

Now if you crawl under there, you will notice an interface socket on the left hand side, about level with the bottom left screw you removed a moment ago. You can click on the image (right) to enlarge...

This is the location of the diagnosis connector, and I believe this is where a MUT-II unit is connected.

As I noted before, though, we don't need a MUT-II to do our dirty work! The EVO manual states...

Earth No. 1 terminal (diagnostic control terminal) of the diagnostic connector. Turn on the ignition switch.

The image to the left was taken with the camera facing directly up. The "top" of the picture is oriented to the rear of the vehicle. Incidentally, the strange circular thing in the centre of the frame is simply the alarm's glass breakage sensor.

As noted before, we must earth No. 1 terminal on this connector. The pin in question is the bottom right one in the picture - highlighted.

All we have to do is ground out this pin by using a single cable. With the engine ignition switch on, the computer will flash the engine warning light to indicate any stored diagnostic code(s).

Because it was a bit of a pain getting in there and grounding this pin, I decided to find a less fiddly way of triggering an error code output...

At the back of the diagnostic plug, it was clear to see that the relevant pin was connected to an easily accessible lead (grey with red stripe on my 1995 GPX, but apparently a different colour on some other FTOs).

I used a standard patch connector to attach an extra wire to the relevant lead (see image to right, highlighted).

Now it is simply a matter of grounding out the permanent diagnostic lead stowed under the dash.

When I get the chance, I will be rewiring this with a push-button switch that will close the connection from pin 1 to earth. Luxury...!

Here are the diagnostic codes, gleaned both from the Workshop Manual and a few other places:

11 Oxygen Sensor
12 Air Flow Sensor
13 Intake air temperature sensor
14 Throttle position sensor
15 ISC Motor Position Sensor
21 Engine coolant temperature sensor
22 Crank angle sensor
23 Camshaft position sensor
24 Vehicle speed sensor
25 BARO Sensor (listed as 26 in one info source)
31 Detonation sensor
32 Vacuum sensor
36 Ignition Timing Adjustment Signal
39 Oxygen Sensor
41 Injector system
42 Fuel Pump
43 EGR
44 Ignition coil and power transistor unit (Cylinder 1 & 4)
52 Ignition coil and power transistor unit (Cylinder 2 & 5)
53 Ignition coil and power transistor unit (Cylinder 3 & 6)
55 Idle Air Control Valve/Servo Valve Position Sensor
61 Communications wire with A/T-ECU
62 Intake air control valve position sensor
64 Alternator FR terminal
71 Vacuum control solenoid valve (TCL)
72 Ventilation control solenoid valve (TCL)

So what does an ECU diagnostic code look like when it is displayed?

Well, it looks a lot like this:

This is blinking out diagnostic code 31. It does so by blinking the engine warning light for 3 long flashes and 1 short flash.

If no codes are currently stored, it will simply flash continually, once per second.

I assume that if more than one code is stored, it will display each one in a repeating sequence, eg. 31, 52, 64, 31, 52, 64...

To clear the codes, simply disconnect the car battery for 20 seconds or so.

Note: I found notes about this procedure on the Smartgroups FTO List, posted by 'troy' in 2001. Legend has it that Dave Hughes originally posted information on this around 1999. Good work to all concerned!

Thanks also to Rob Jay for pointing me at a load of extra codes that didn't feature in the workshop manuals.

(c) 2002, All Rights Reserved