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2021 Ascent Limited - Key Fob Not Detected / Push Button Start Failure

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Emily N. · rep 0 · May 22, 3:18 AM · 1 replies · solved · Question

Vehicle: 2021 Subaru Ascent Limited

I'm having a really frustrating problem with my 2021 Subaru Ascent Limited. Sometimes, when I try to start the car using the push-button start, I get a "Key Fob Not Detected" message, even when the fob is right in my hand or in the cupholder. I've tried both of my key fobs, and they both do it intermittently.

I've replaced the battery in one of the fobs, but it didn't help. It usually takes several tries, or I have to hold the fob right up to the start button, for it to finally recognize it. Is this a common issue with the smart key system, or could it be a bigger electrical problem with the car itself?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:18 AM

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ClearTheCode admin answer:

The "Key Fob Not Detected" message on your 2021 Subaru Ascent Limited, especially when intermittent and affecting both fobs, points to an issue with the vehicle's keyless access and push-button start system. This can be more than just a simple fob battery problem.

  1. Key Fob Battery (Re-check):

    • Even if you replaced one, ensure the new battery is fresh and correctly installed. Try replacing the battery in both fobs to rule out a weak fob battery completely. Use a high-quality CR2032 battery.
    • Important: The Ascent has a specific procedure for starting when the fob battery is dead: hold the fob directly against the push-button start button. If this consistently works when the normal method fails, it strongly suggests a weak fob battery or a communication issue.

  2. Vehicle's Receiver/Antenna System:

    • Your Ascent has multiple antennas located around the cabin that detect the key fob's signal. If one of these antennas or its wiring is faulty, it can lead to intermittent detection issues.
    • Interference: Other electronic devices in the car (e.g., phone chargers, dash cams, even certain cell phones) can sometimes interfere with the key fob's signal. Try removing all other electronic devices from the cabin to see if the problem resolves.

  3. Vehicle Battery Voltage:

    • While less common for this specific issue, a weak 12V car battery can sometimes cause various electrical gremlins, including issues with keyless entry and starting systems. Have your main car battery tested.

  4. Immobilizer System/Smart Key Control Module:

    • The vehicle's immobilizer system and the Smart Key Control Module are responsible for recognizing the key fob and allowing the engine to start. A fault in this module or its programming can cause detection failures.

Common OBD-II Codes (Dealership Level): While a Check Engine Light is unlikely, a Subaru-specific diagnostic tool might reveal B-codes related to the keyless access system, such as:

  • B2200 series: Related to key fob communication or immobilizer system faults.
  • B2201, B2202: Key ID registration errors.
  • B2203: Keyless access antenna issues.

When to See a Shop: Since you've already tried replacing a fob battery and the issue persists with both fobs, it's highly recommended to take your Ascent to a Subaru dealership. They have the specialized diagnostic tools (Subaru Select Monitor) to:

  • Read specific B-codes from the Smart Key Control Module.
  • Test the signal strength and functionality of the vehicle's keyless access antennas.
  • Check for any software updates for the keyless entry system.
  • Diagnose and potentially replace a faulty Smart Key Control Module or related wiring.
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