To test your engine, first start it up and let it reach normal operating temperature. Then shut the engine off and proceed with work at the diagnosis connector. Using an unfolded paper clip, connect the GND and the TEN pins together. Return to the driver's seat and turn your ignition key to "ON" but do not start the engine.
Observe the "CHECK ENGINE" light in your instrument panel. It will flash a certain number of times to indicate a malfunction in your engine's control system. Count the number of flashes to indicate the malfunction code.
If the code is a two-digit number, the "tens" digit will be displayed first, then for a short 1.6-second period the light will be dark, then the "ones" digit will be displayed. This will repeat after a four-second dark pause. If there are multiple codes, they will each be separated by a four-second pause and may include two-digit codes, so pay attention.
Take as long as you need to record the codes and then refer to the chart below or section "F" of your factory service manual.
Note that the following codes are for '93 and older models. Beginning in '96, the Miata used OBD (On-board diagnostics) which requires a special scanner to read the codes.
FAULT CODES ('90-'93)
1 Ignition pulse (No Igf signal)
2 No Ne signal
3 No G signal
8 Airflow meter open or short circuit
9 Water thermistor open or short circuit
10 Intake air thermistor in airflow meter open or short circuit
12 Throttle position sensor open or short circuit
14 Atmospheric pressure sensor open or short circuit
15 Oxygen sensor <0.55 V 180 sec after 1500 rpm
17 Oxygen sensor unchanged after 1500 rpm
25 PRC solenoid valve
26 Solenoid valve (Evaporative canister purge)
34 ISC Valve