MX5 NA fault codes

 I'm putting this here as I've finally found an appropriate collection of information that will help now I have reinstated the diagnostic port. I originally removed the port because I thought it just gave the ability to check various voltages in the circuit. Given I'm not working on an original MX5 I figured I could just check the actual wiring. Unfortunately it's got a couple of extra pins that aren't replicated anywhere else.

First option it gives is setting the base idle. Given that I have a slight idling issue I thought this could come in handy.

Connecting the TEN pin to Ground using a piece of wire removes the ECU control of the idle speed and leaves it entirely up to the throttle body. On the throttle body itself there is an idle screw, it's in a short cylinder and sometimes covered by a rubber bung (mine isn't which is a bit worrying as it suggests someone else has already had a go at it). 

With all electrics off, the engine running and up to temperature, connect TEN to Ground, then adjust idle to get to 850-900 RPM. Then remove the connector. Nice and simple

The second is some fault codes of sorts. It's not a posh OBDII interface that requires a dongle or similar, it's more like the old Vauxhall option that I remember from when I was a kid. 

With the engine off this time, connect an LED (with current limiting resistor) from the FEN pin to the battery. (Or in my case as I don't have a battery connection immediately available, spend at least ten minutes trying to find an accessible positive which could be entertaining as the IVA required them all to be covered and protected!). Turn the ignition on and look for the LED lighting up for five seconds (if it doesn't, it's backwards, however considering I'm connecting one side to battery I'm going to assume that's the positive on the LED).

After the initial check, it should flash any error codes as below;

• 1 Ignition pulse
• 2 Ne signal [Crank angle sensor]
• 3 G signal [crank angle sensor ground?]
• 4 SGT signal (1.8L)
• 8 Airflow meter
• 9 Water thermistor
• 10 Intake air thermistor in airflow meter
• 12 Throttle position sensor
• 14 Atmospheric pressure sensor
• 15 Oxygen sensor (output too low)
• 16 EGR function sensor (1.8L)
• 17 Oxygen sensor (output not changing)
• 25 PRC solenoid valve (1.8L)
• 26 Solenoid valve (Evaporative canister purge)
• 27 EGR solenoid valve (vacuum)(1.8L)
• 28 EGR solenoid valve (vent)(1.8L)
• 34 Idle air control valve

For the two digit codes, it flashes the ten's digit first with longer flashes, then pauses before flashing the one's digit with shorter flashes). It loops round the codes so it can be double checked. 

For my car I'm expecting at least some codes, for example the evap canister isn't there anymore so '26' is almost guaranteed.

Lastly the diagnostic plug pinout with the relevant coloured wires. This was built up from various sources on the assumption that I had binned my diagnostic plug and I was going to have to come up with another solution. As it turns out, I still had my diagnostic plug with at least the important wires still attached, but at least this list would have given me an alternative;

• 2. LT GRN-YEL to Conn#1 K (ignition adjustment connector) (TEN terminal) Test
• 3. WHT-GRN to Conn#1 D (Data link) (MEN Terminal) Monitor
• 4. WHT-YEL to Conn#1 F (Data link) (FEN Terminal) Faults
• 15. BLK to GND
• 17. WHT-RED to Conn#1 B and Power and Fuel injectors (engine control relay)
• 18. GRN-ORG to Horn Relay
• 20. BLK-GRN to Cooling Fan Relay
• 21. BLK to GND
• 22. YEL-BLU to Igniter
• 23. RED to airbags

In my case I've only got the first four, as mentioned the fifth wire for battery might have been useful but I can live without it. 

So that's a task for this weekend (or maybe one evening this week). Work has been ridiculous though so I've not had chance to do any work. I'm even typing this while watching something process at work, just because I've not had any other time available.