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2019 Mazda MX-5 Miata - 'Key Not Detected' Error, Won't Start

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Mike T. · rep 0 · May 25, 3:35 AM · 1 replies · solved · Question

Vehicle: 2019 Mazda MX-5 Miata Club

Hi everyone,

I have a 2019 Mazda MX-5 Miata Club, and I'm suddenly having trouble starting it. When I press the start button, I get a 'Key Not Detected' message on the dash, and the car won't crank. I've tried both of my key fobs, and neither works. I even replaced the battery in one of the fobs, but no luck.

The lights and radio still work, so it doesn't seem like a main car battery issue. I've tried putting the fob right up to the start button, which usually works as a backup, but still nothing. This is really frustrating, especially since it happened out of the blue.

Has anyone experienced this with their Miata or other Mazda models with push-button start? What could be causing the car to not detect the key?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:35 AM

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ClearTheCode admin answer:

The 'Key Not Detected' error in a push-button start system like your 2019 Mazda MX-5 Miata indicates that the vehicle's immobilizer system isn't recognizing the proximity key fob. This prevents the car from starting as a security measure.

  1. Key Fob Battery (Re-check): Even though you replaced one, ensure the new battery is correctly installed (positive/negative orientation) and is a fresh, high-quality CR2025 or CR2032 (depending on your fob model). Try the second fob again, even if you haven't replaced its battery, as a fresh battery is often the simplest fix.
  2. Backup Starting Procedure: Mazda vehicles usually have a backup method for starting when the key fob battery is low or signal is weak. This typically involves pressing the key fob directly against the start button while pressing the brake pedal. If this isn't working, it suggests the issue might be with the car's receiver or immobilizer system rather than just the fob's battery.
  3. Check for Signal Interference: Sometimes, strong radio frequency (RF) interference from nearby electronics (e.g., cell towers, power lines, other electronic devices in the car or your pocket) can temporarily block the key fob's signal. Try moving the car to a different location if possible, or turning off any personal electronic devices.
  4. Vehicle 12V Battery Condition: While you mentioned lights and radio work, a weak car battery (even if not completely dead) can sometimes cause electrical anomalies, including issues with key detection or immobilizer systems. Have your car's main 12V battery tested.
  5. Immobilizer System Components:
    • Key Fob Transponder: The fob contains a transponder chip that communicates with the car. If this chip is damaged, the car won't recognize it.
    • Antenna/Receiver: The car has antennas (often located around the cabin) that pick up the key fob's signal. A faulty antenna or its wiring can prevent detection.
    • Immobilizer Control Module: This module manages the communication between the key and the engine control unit (ECU). A fault here would prevent starting.

When to See a Shop:

If replacing the key fob batteries, trying the backup start procedure, and checking for interference don't resolve the issue, it's time to have your Miata towed to a Mazda dealership. They have specialized diagnostic tools (like the Mazda Modular Diagnostic System - M-MDS) that can communicate with the immobilizer system, read specific trouble codes (e.g., B2477 - Module Configuration Failure, B247A - Key Fob Malfunction), and pinpoint whether the problem lies with the key fobs themselves (requiring reprogramming or replacement), the car's antenna, or the immobilizer control module. This is a security-critical system, so professional diagnosis is essential.

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