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"Key Not Detected" Issue with 2021 CX-5 Push-Button Start

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Mike T. · rep 0 · May 22, 4:50 AM · 1 replies · solved · Question

Vehicle: 2021 Mazda CX-5 Carbon Edition

My 2021 Mazda CX-5 Carbon Edition has been giving me a frustrating "Key Not Detected" message when I try to start it. Sometimes it takes several tries, or I have to hold the key fob right up to the start button for it to register. This happens with both of my key fobs, which makes me think it's not just a bad fob battery.

I've already replaced the battery in both key fobs, but the problem persists. It's becoming a real hassle, and I'm worried about getting stuck somewhere. Is this a common problem with the push-button start system in these Mazdas, and what could be the underlying electrical cause?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:50 AM

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ClearTheCode admin answer:

The "Key Not Detected" message, especially when affecting both key fobs and after battery replacement, points to an issue with the vehicle's keyless entry and start system. This is an electrical communication problem. Here's what could be happening:

  1. Key Fob Battery (Re-check): Even new batteries can sometimes be faulty or incorrectly installed. Double-check the orientation and ensure they are fresh, high-quality batteries. Also, ensure there isn't any corrosion inside the fob.
  2. Vehicle's Keyless Antenna System: Your CX-5 has multiple antennas located throughout the cabin and exterior to detect the key fob's signal. If one or more of these antennas are faulty, damaged, or have loose connections, the car won't reliably detect the key. This is a common cause for this symptom.
  3. Immobilizer System Malfunction: The immobilizer system, which prevents the car from starting without the correct key, could be experiencing an electrical fault. This system relies on communication between the key fob, antennas, and the vehicle's computer.
  4. RF Interference: While less common, strong radio frequency interference from external sources (e.g., nearby cell towers, power lines, or even other electronic devices in the car) can sometimes disrupt the key fob's signal.
  5. Low Vehicle Battery: A weak 12V car battery can sometimes cause strange electrical gremlins, including issues with key detection, as various modules may not receive stable voltage.

OBD-II Scan: A diagnostic scan tool can often reveal specific codes related to the keyless entry and immobilizer system. Look for B-codes (Body codes) such as:

  • B1026: Keyless Entry Antenna Malfunction (specifying which antenna)
  • B1027: Ignition Switch Malfunction (related to the push-button start itself)
  • B1028: Immobilizer System Malfunction

When to See a Shop: Since you've already replaced the key fob batteries, it's highly recommended to take your CX-5 to a Mazda dealership or a specialized automotive locksmith/electrical shop. They have the advanced diagnostic tools to pinpoint which antenna is failing, if there's a wiring issue, or if a control module needs attention. This is not a DIY fix for most owners, and professional diagnosis is essential to avoid being stranded.

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