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2021 GX 460 'Key Not Detected' Warning & Push Button Start Issues

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Nicole W. · rep 0 · May 22, 4:43 AM · 1 replies · solved · Question

Vehicle: 2021 Lexus GX 460 Premium

Hi everyone, I'm having a really annoying problem with my 2021 Lexus GX 460 Premium. Sometimes when I get in the car, I get a 'Key Not Detected' warning on the dash, even though the key fob is right there in my pocket or the cup holder. This makes it impossible to start the car with the push-button start.

I've tried replacing the battery in both of my key fobs, but the issue still pops up randomly. It's intermittent, which makes it hard to diagnose. Any ideas what could be causing this? Is it a car battery issue or something with the smart key system?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:43 AM

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ClearTheCode admin answer:

The 'Key Not Detected' warning on your 2021 Lexus GX 460, especially after replacing key fob batteries, points to an issue with the vehicle's smart key system or related electrical components. Here's a breakdown of potential causes and troubleshooting steps:

  1. Vehicle's 12V Battery Health: While you've focused on the key fob, a weak or failing 12V car battery can cause a myriad of electrical gremlins, including issues with the smart key system. Even if it starts the car, low voltage during startup or while the car is off can affect sensitive electronics. Have your main car battery tested for CCA (Cold Cranking Amps) and overall health.
  2. Key Fob Placement: Ensure there are no other electronic devices (like another phone, RFID cards, or even other car keys) directly next to your key fob, as these can sometimes interfere with the signal.
  3. Smart Key System Antennas: Your GX 460 has multiple antennas located throughout the cabin (e.g., in the center console, under the seats, in the trunk) that detect the key fob's signal. If one of these antennas is faulty, disconnected, or obstructed, it can lead to intermittent detection issues. Damage to the wiring for these antennas is also possible.
  4. Smart Key ECU/Module: The smart key system is controlled by a dedicated Electronic Control Unit (ECU). A fault within this module can cause incorrect key detection. This might trigger specific diagnostic trouble codes (DTCs) related to the smart key system, such as B2780 (Key Transponder Malfunction) or B2784 (Smart Key System Malfunction).
  5. Interference: Strong external radio frequency (RF) interference in certain locations (e.g., near cell towers, power lines, or specific industrial equipment) can sometimes temporarily disrupt the key fob's signal.

Temporary Workaround: If you get the 'Key Not Detected' warning and can't start the car, try holding the key fob directly against the push-button start button. There's usually an emergency transponder coil in the button that can read the key's chip even if the RF signal isn't being detected by the main antennas.

When to See a Shop: Since you've already replaced the key fob batteries and the issue is persistent, it's best to take your 2021 GX 460 to a Lexus dealership. They have the specialized diagnostic tools (Techstream) to read specific smart key system codes, test the functionality of all smart key antennas, and diagnose if the smart key ECU or any related wiring needs attention. This is a complex system, and professional diagnosis is crucial for a correct and lasting repair.

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