San Diego Miata Club

Engine Diagnostic Codes

Submitted by "Voodoo" Bob Krueger

You don't need a special tool to read a Miata's diagnostic codes. There is an article on this subject in the Tipsheet section of the Summer '94 issue of Miata Magazine on page 25.

Basically, what you do is locate the diagnostic connector, which is a little black box with a flip-top lid that sits atop the driver's side shock tower. First, start your engine and lt the car run until it is warmed up. Shut the engine off. Open the lid of the diagnostic connector and place an expanded paper clip between the TEN and GND pins (there is a legend of which pin is which on the underside of the lid). These are the same pins that you short to adjust the timing.

Go back to the driver's seat and turn your ignition switch to the "ON" position but DO NOT start the engine. Observe the "check engine" light. If there are codes to be downloaded, the ligt will flash to indicate them. You need to watch closely enough to count the flashes. If the code is a two-digit number, the tens digit will be displayed first, followed by a 1.6-second pause and then the display of the ones digit. The code will repeat after a 4-second dark pause. If there are multiple codes to report, they will each be separated by 4-second dark pauses. As any of these multiple codes may also be two-digit numbers, the key is to pay close attention to all this flashing.

The table that deciphers the codes is in section F of your factory shop manual, if you have one. If you don't, they are shown below. Rod Grainger's Miata Enthusiast's Manual has a more comprehensive description of what the codes mean and what to do about them in section 5:12, but only for the 1.6-liter cars.

1 - Ignition pulse
2 - No signal
3 - G signal
4 - SGT signal (1.8-liter)
8 - Airflow meter
9 - Water thermistor
10 - Intake air thermistor in air flow meter
12 - Throttle position sensor
14 - Atmospheric pressure sensor
15 - Oxygen sensor (output too low)
16 - EGR function sensor (1.8-liter)
17 - Oxygen sensor, output not changing
25 - PRC solenoid valve (1.8-liter)
26 - Solenoid valve (evaporative canister purge)
28 - EGR solenoid valve (vacuum or vent - 1.8-liter)
34 - Idle air control valve (1.8-liter)
36 - Idle speed control valve

To clear the codes from the computer, remove the "BTN" fuse from the underhood main fuse box for twenty seconds and then reinstall it. This fuse box is on the passenger side fender well inside the engine compartment.


Please note that these tips and pointers are not reviewed or approved by Mazda Motor Corporation or any other corporation or entity other than the originator. The San Diego Miata Club does not accept any liability for damage or injury as a result of utilizing these tips and pointers. Please use common sense and always remember safety first.