What Does B3109 Mean?
This diagnostic trouble code indicates that the Body Control Module (BCM) has detected a low voltage condition from the keyless entry remote transmitter (key fob). The BCM monitors signal strength and voltage levels transmitted by the key fob during communication attempts. When the battery voltage in the remote falls below the manufacturer's specified threshold, this code is set to alert the user that the transmitter battery needs replacement soon.
Common Causes
70%
Depleted or weak key fob battery nearing end of service life
15%
Corroded or dirty battery contacts inside the key fob housing
10%
Faulty key fob internal circuitry or damaged antenna
5%
BCM receiving module sensitivity issue or software calibration error
Diagnostic Steps
1
Step 1: Test the current key fob battery voltage using a digital multimeter - should read 3.0V or higher for CR2032/CR2025 type batteries (specification varies by battery type, check marking on battery)
2
Step 2: Inspect the key fob battery contacts for corrosion, dirt, or damage; clean contacts with electronics cleaner and verify proper spring tension on contact points
3
Step 3: Replace the key fob battery with a new OEM or quality replacement battery, ensuring correct polarity and proper seating in the battery compartment
4
Step 4: Test key fob operation from various distances (10, 20, 30 feet) to verify normal unlock/lock/panic functions and adequate signal strength
5
Step 5: Clear the DTC from the BCM and perform a drive cycle or multiple lock/unlock operations to confirm the code does not return
6
Step 6: If code persists after battery replacement, test with a known-good spare key fob to isolate whether the issue is with the specific transmitter or the vehicle's receiver system
Estimated Repair Cost
$5 - $150
Parts + labor, varies by vehicle and location
This diagnostic trouble code indicates that the Body Control Module (BCM) has detected a low voltage condition from the keyless entry remote transmitter (key fob). The BCM monitors signal strength and voltage levels transmitted by the key fob during communication attempts. When the battery voltage i...
The most common cause of B3109 (Keyless Entry Transmitter Low Battery) is: Depleted or weak key fob battery nearing end of service life
Typical repair costs for B3109 range from $5 to $150, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving. This is a convenience feature warning only. If the battery fully depletes, you may be unable to unlock/lock the vehicle remotely and may need to use the physical key blade or approach-based passive entry if equipped.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B3109 to identify the root cause.
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Quick Info
Category
Body
System
Keyless Entry / Body Control System
Difficulty
Type
Manufacturer
Recommended Tools
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