Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSMAZDA1999MX-5 MIATA L4-1.8L DOHCREPAIR AND DIAGNOSISRELAYS AND MODULESRELAYS AND MODULES - TRANSMISSION AND DRIVETRAINRELAYS AND MODULES - A/TCONTROL MODULETESTING AND INSPECTION
1999 Mazda MX-5 Miata L4-1.8L DOHC
Control Module: Testing and Inspection
1999 Mazda MX-5 Miata L4-1.8L DOHCSECTION Testing and Inspection
TRANSMISSION CONTROL MODULE INSPECTION
1. Turn the ignition switch to ON, and inspect the transmission control module terminal voltage, referring to the Terminal Voltage Chart.
2. If any transmission control module terminal voltage is incorrect, inspect the related input of output devices and wiring. If no problem is found, replace the transmission control module.



Terminal Voltage Chart (Reference Data)
Note: Use the ground of terminal AP of the transmission control module when measuring terminal voltage as an error may occur when the negative (-) lead of the circuit tester is connected to ground.
1. Turn the ignition switch to ON, and inspect the transmission control module terminal voltage, referring to the Terminal Voltage Chart.
2. If any transmission control module terminal voltage is incorrect, inspect the related input of output devices and wiring. If no problem is found, replace the transmission control module.
Terminal Voltage Chart (Reference Data)
Note: Use the ground of terminal AP of the transmission control module when measuring terminal voltage as an error may occur when the negative (-) lead of the circuit tester is connected to ground.
RENDER: 1.0x
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.