MK1 Diagnostic Fault Codes

How to run the diagnostics on a Mazda MX5 MK1


Some of these codes are common with MK2s BUT haven’t checked them yet.


There are a few things you need before you start:


  • A jumper – this can be as simple as a paper clip
  • An LED – ideally one you can actual see
  • The ability to count! If you can’t count then you shouldn’t be trying this!


Note: Some codes are specific to 1.8s


You can buy a great book written by John Cookson which includes the LED and much more detailed instructions. It’s about £10 inclusive and probably the best little book you’ll ever buy for your MX5.


Here’s the link – Diagnostic Book


1. Check the Obvious Things on the Car


Have may want to check the following:


  • Fuses
  • Fuel – is there any in the tank? Remember the fuel is under pressure in the fuel rail!
  • Ignition – is there a spark
  • HT Leads – MX5s tend to consume these every 30k miles so it might be worth checking them.
  • Immobiliser
  • Is the timing or cam belt broken?
  • How’s the engine compression?


It’s worth thinking about these before you start work….


2. First you need to locate the DiagnosticPort


You’ll find the diagnostic port on the right hand side of the engine as you are looking into the bonnet. It’s a little box about 50mm x 30mm.



Open the lid – there’re some helpful descriptions / labels inside the lid.




3. Plug the “jumper” in to ports GND and TEN






This over-rides the control functions of the ECU. (This is also how you set the base idle.)


Some faults mean the car won’t start but the ECU will hold fault codes.


4. Plug the LED in to ports FEN and +B


Plug the LED negative terminal into the FEN port.


Plug the LED positive terminal into the +B port.


NOTE: Port +B is a direct connection to the battery!





5. Switch Ignition On


The LED will illuminate for 3 seconds – this in confirming that the diagnostic system is operational.


6. Read the Fault Codes


Fault codes are reported as a series of flashes.


A long flash (1.2 seconds) = 10 digits in fault codes.


A short flash ((0.4 seconds) = one digit in fault codes.


Write these codes down and check the list for details





Examples of fault codes:


Three long flashes and four short flashes = 3x10 plus 4x1 = 34 (Idle Speed Control Value)


Eight short flashes = 8x1 = 8 (Airflow Meter)


7. List of Codes


This is a list of codes:


01 – Ignition Pulse – No signal – check the igniter, coils and wiring.


02 – Ne Signal – No Signal – Check Cam Angle Sensor


03 – G Signal (or SGT on 1.8) - Check Cam Angle Sensor


04 – SGC Signal (1.8) - Check Cam Angle Sensor


08 – Airflow Meter – Open or Short Circuit


09 – Water Thermistor – Open or Short Circuit


10 – Intake Air Thermistor in Airflow Meter - – Open or Short Circuit


12 – Throttle Position Sensor (TPS) – Open or Short Circuit


14 – Atmospheric Pressure Sensor - – Open or Short Circuit


15 – Oxygen Sensor (output low) – Sensor or Wiring Fault


16 EGR Function Sensor (1.8) – Open or Short Circuit


17 – Oxygen Sensor (output not changing) – Lean / Rich Running Fault


25 – PRC Solenoid Value (1.8) - – Open or Short Circuit


26 – Solenoid Value (Evaporative Canister Purge) – Open or Short Circuit


28 – EGR Solenoid Value (Vacuum 1.8) – Open or Short Circuit


29 – EGR Solenoid Vale (Vent 1.8) – Open or Short Circuit


34 – Idle Speed Control Value – Open or Short Circuit


8. Solve the Problem and Re-Test



There is a whole load more information in John’s book – buy it – it’s really is an invaluable tool!