How To Change The Battery On A Subaru Key Fob: A Complete Step-by-Step Guide

To change the battery on a Subaru key fob, release the integrated emergency metal key by pressing the silver release button on the back of the transmitter, then insert a microfiber-wrapped flathead screwdriver into the designated split line or slot to gently pry the two housing halves apart. Replace the depleted coin-cell battery (typically a CR2032 or CR1632) with a new 3-volt lithium cell, ensuring the positive (+) side is facing the correct direction as specified by your specific fob layout. Snap the housing halves firmly back together until they click, slide the mechanical key back into its slot, and test the lock/unlock functions to verify operation.

Required Equipment, Battery Specifications, and Safety Prep

Before attempting to open your Subaru key fob, you must gather the correct tools and understand the technical specifications of your transmitter. Using improper tools or forcing the plastic housing can damage the internal printed circuit board (PCB), strip the ABS plastic parting lines, or ruin the water-resistant silicone gasket, leading to an expensive replacement.

Most modern Subaru models—including the Outback, Forester, Crosstrek, WRX, Legacy, Impreza, and Ascent—utilize either a rectangular smart key with push-button start or an older teardrop-style remote key. These transmitters rely on high-energy lithium manganese dioxide (Li-MnO2) coin-cell batteries, which operate at a nominal 3 volts. When the battery voltage drops below 2.8V, the transmitter's range degrades, and the vehicle's multi-information display (MID) will trigger a low key fob battery warning.

Pre-Procedure Checklist

• Essential Gear and Tools:
  
  
  • A new replacement lithium coin-cell battery (either CR2032 or CR1632/CR1620, depending on your model year).
  • A small flathead screwdriver (blade width of 2.0mm to 3.5mm) or a specialized plastic spudger tool.
  • A clean microfiber cloth (to wrap around metal tools to prevent scratching or gouging the fob's casing).
  • Anti-static wrist strap or a clean, grounded, non-conductive workspace (highly recommended to prevent Electrostatic Discharge (ESD) damage to the internal integrated circuits).
• Mandatory Prerequisite Knowledge:
  
  
  • Understand your Subaru’s starting system: Vehicles equipped with Keyless Access and Push-Button Start (PEPS system) use a high-draw CR2032 smart key fob, while turn-key ignitions typically use a CR1620 or CR1632 integrated key remote.
  • Familiarity with polarity orientation: Inserting the coin-cell battery upside down will prevent the fob from functioning and can damage the contact terminals.
• Estimated Budget and Duration:
  
  
  • Cost: $3.00 to $8.00 (depending on battery pack size and brand).
  • Time Required: 3 to 5 minutes of focused assembly work.

Step-by-Step Key Fob Disassembly and Battery Installation

The following step-by-step procedure is optimized for Subaru key fobs manufactured from 2015 to the present. If your Subaru utilizes an older physical key integrated with remote buttons, the disassembly process is highly similar, but you will access the internal transmitter module rather than a direct open-back plate.

Step 1: Release and Extract the Emergency Mechanical Key

The mechanical emergency key acts as a physical lock for the key fob housing. To begin, look at the back of your Subaru key fob and locate the small, silver, rectangular release button.

1. Use your thumb to depress the silver release button fully.
2. While holding the button down, pull firmly on the metal key ring attachment at the top of the fob.
3. The mechanical key blade will slide cleanly out of its internal chamber.
4. Set the emergency key aside on a clean surface.

Step 2: Pry Open the Outer ABS Housing Halves

Once the mechanical key is removed, you will see the empty slot where the key blade was stored. Inside or directly adjacent to this channel, there is a dedicated prying notch.

1. Wrap the tip of your flathead screwdriver in a single layer of a microfiber cloth to buffer the metal blade.
2. Insert the wrapped screwdriver tip directly into the small slot located near the edge of the key slot opening.
3. Gently twist the screwdriver clockwise or counterclockwise. Do not use an upward prying motion, as this can break the plastic retaining clips.
4. You will hear a distinct popping sound as the internal plastic retaining tabs release.
5. Continue to slide your tool along the seam of the key fob to completely split the front and back covers of the housing.

Warning: Do not insert the screwdriver deep into the fob cavity. Doing so can scratch the printed circuit board, sever copper traces, or dislodge surface-mount capacitors, rendering the transponder inoperable.

Step 3: Access the Internal Circuit Board and Battery Compartment

With the housing split open, you will see the internal structure. Depending on your Subaru fob model, the battery may be visible immediately, or it may be protected by a circular silicone cover designed to prevent moisture ingress.

1. Carefully lift the rubber or silicone moisture barrier off the assembly if your model is equipped with one.
2. Note the orientation of the printed circuit board. In some fobs, the circuit board will stay resting in the front faceplate. If the PCB comes loose, hold it only by its non-conductive edges.
3. Locate the coin-cell battery, which is held in place by metallic spring contacts.

Pro-Tip: Static electricity can instantly destroy a key fob’s CMOS memory chip. Touch a grounded metal object before handling the internal green circuit board, or wear powder-free nitrile gloves to shield the components from skin oils and electrostatic transfer.

Step 4: Extract and Replace the Depleted Coin-Cell Battery

Removing the battery must be done with precision to avoid bending the delicate brass or tin-plated spring tension contacts that complete the electrical circuit.

1. Slide your thin, non-conductive pry tool (or your screwdriver wrapped in cloth) underneath the edge of the old battery.
2. Pop the battery out of its retaining ring. Avoid pressing against the side tension clips, which can easily snap or lose their tension.
3. Inspect the metal contact points inside the battery tray. If they appear oxidized or dusty, clean them using a cotton swab lightly dampened with 90%+ isopropyl alcohol, then let them dry completely.
4. Slide the new, fresh battery into the tray. For most modern Subaru smart fobs (CR2032), the battery must go in with the positive (+) side facing UP, meaning the written branding and "+" symbol are fully visible to you.
5. Press down gently until the battery clicks under the metal retaining clips.

Step 5: Reassemble and Verify Transmitter Operation

Reassembling the fob requires proper alignment of the weatherproofing gaskets to ensure the fob remains sealed against rain and accidental spills.

1. Place the silicone moisture barrier back over the battery and circuit board, ensuring it seats flush in its guide channels.
2. Align the front and back halves of the plastic key fob housing.
3. Squeeze the two halves together firmly starting at the top, moving your fingers down the sides to the bottom. You should hear a sequence of sharp clicks as the perimeter clips latch.
4. Inspect the seam around the entire fob to ensure there are no uneven gaps.
5. Slide the emergency mechanical key back into its slot until it locks with an audible click.
6. Stand near your vehicle and press the lock or unlock button. The parking lights should flash, confirming successful installation and signal transmission.

Subaru Key Fob Specifications, Battery Sizes, and Transmitter Metrics

The table below outlines the specific technical configurations for various Subaru model generations, including exact battery numbers, tool requirements, and active transmitter frequencies.

Subaru Key Fob Common Failures and Field Diagnostics

If you encounter issues after completing a battery swap, do not panic. Most post-installation issues are mechanical or electrical, rather than programming losses. Use the troubleshooting matrix below to isolate and fix the fault.

• Scenario 1: The key fob is completely dead and unresponsive after installing the new battery.
  
  
  • Root Cause: The new battery was installed upside down (reverse polarity), or the positive and negative metal contact tabs inside the fob have been flattened, losing contact with the battery.
  • Actionable Fix: Re-open the fob and verify that the positive (+) side of the battery is facing the correct direction. If the orientation is correct, check the metal contact fingers. Gently use a sewing needle or precision pick to bend the contacts slightly upward so they apply firmer pressure to the battery surface.
• Scenario 2: The range of the key fob is extremely limited, requiring you to be right next to the driver's door.
  
  
  • Root Cause: The replacement battery is defective or has sat on a retail shelf for too long, causing its voltage to drop below the optimal 3.0V threshold under load. Alternatively, cheap off-brand batteries may lack the necessary current discharge rate.
  • Actionable Fix: Use a digital multimeter to test the open-circuit voltage of the coin-cell battery. If it registers below 2.9V, discard it and install a premium-grade, name-brand (such as Panasonic, Energizer, or Duracell) lithium cell.
• Scenario 3: The dashboard displays a "Key Not Detected" warning even with a brand-new battery.
  
  
  • Root Cause: The internal passive transponder chip is failing to communicate with the vehicle's low-frequency (LF) interior antennas due to interference, or the transponder coil inside the fob has cracked from drop damage.
  • Actionable Fix: To bypass this and start the car, hold the physical key fob directly against the Push-to-Start ignition button while depressing the brake pedal. This utilizes a near-field magnetic coupling system (similar to RFID) that powers the transponder even if the fob’s active signal transmitter is failing.
• Scenario 4: The buttons feel mushy and do not actuate the lock or unlock functions, though the red LED light flashes.
  
  
  • Root Cause: The internal silicone button membrane has misaligned during reassembly, or dirt and hand oils have migrated under the carbon contact pads on the PCB.
  • Actionable Fix: Disassemble the key fob once more. Clean the carbon contacts on both the bottom of the rubber membrane buttons and the corresponding gold contact pads on the circuit board using 99% isopropyl alcohol. Realign the membrane meticulously before snapping the outer shell back together.

Frequently Asked Questions

Does changing my Subaru key fob battery reset its programming?

No, changing the battery will not wipe or reset your key fob's transponder programming. The rolling-code synchronization and vehicle-specific immobilizer data are written to non-volatile EEPROM memory within the fob's microprocessor, which retains all pairing information indefinitely even when completely disconnected from a power source.

Why is there a red light flashing on my key fob but the car won't open?

A flashing red LED indicates that the key fob is successfully receiving power from the battery and attempting to broadcast an ultra-high frequency (UHF) RF signal. If the car does not respond, the vehicle's receiver may be experiencing radio-frequency interference from local cell towers or power lines, or the fob's rolling code has desynchronized from the vehicle's Body Control Module (BCM), requiring a dealership system reset.

How do I start my Subaru if the key fob battery dies completely?

If your smart key fob is completely dead, use the integrated emergency metal key to manually unlock the driver's door lock cylinder. Once inside, sit in the driver's seat, press the brake pedal, and press the back of the key fob (the side with the Subaru logo) directly against the Engine Start/Stop button; the car's immobilizer ring will detect the passive RFID chip inside the fob and allow the engine to start.

What is the average lifespan of a Subaru key fob battery?

Under typical driving conditions, a high-quality CR2032 battery in a Subaru keyless access fob will last between two and three years. Smart key fobs with passive entry system capabilities drain batteries faster because they continuously transmit and listen for low-frequency ping signals from the vehicle's proximity sensors.

Maximize Your Subaru's Reliability

To prevent unexpected lockouts, always keep a spare pack of high-quality lithium coin-cell batteries in your glove box or at home. If replacing the battery does not restore full functionality, schedule an diagnostic appointment with your local certified Subaru service center to inspect your keyless entry system.