Code
B3109
HUMMER
B — Body
3 consecutive low battery signals from the same programmed transmitter
AI status
Completed
Completed
100%
Causes
- Weak or depleted transmitter (key fob) coin cell battery
- Corroded or dirty battery contacts inside the transmitter
- Damaged or failing transmitter (internal component or antenna)
- Poor RF reception at the vehicle (antenna/receiver/grounding/wiring fault)
- Interference on the RF frequency or marginal transmitter output
- BCM or receiver module software/firmware anomaly or internal fault
Symptoms
- Instrument cluster or message center shows a low key battery or transmitter low-battery warning
- Reduced remote range or intermittent remote operation
- Remote start, keyless entry, or panic alarm may not work reliably
- One specific programmed transmitter consistently flags a low-battery warning while others work normally
- No obvious door unlock / lock response from that transmitter at normal range
What to check
- Use a scan tool to confirm DTC B3109 and view any related BCM/RCM entries and which transmitter ID is reported
- Attempt to reproduce the condition with the suspect transmitter and note distance/range and function
- Visually inspect the transmitter for damage, corrosion, moisture, or loose battery contacts
- Measure coin cell battery voltage in the transmitter (remove battery unless manufacturer instructions advise otherwise)
- Test a known-good spare transmitter to compare behavior and range
- Inspect receiver/antenna connectors and wiring for continuity, corrosion, and secure grounds
Signal parameters
- Typical RF band: 315 MHz (NA) or 433/868 MHz depending on market
- Transmitter battery nominal: ~3.0 V (CR2032/CR2025 types). Low threshold often considered
- BCM logic: three consecutive low-battery status packets from same transmitter triggers B3109
- RSSI/received signal amplitude lower than expected for normal operation
- Rolling-code packet ID or transmitter serial may be stored with the event (check scan tool data)
Diagnostic algorithm
- Connect compatible scan tool, read and record DTCs and transmitter ID referenced by B3109. Do not clear codes yet.
- Confirm symptom: operate suspect transmitter at close range and normal range; note whether functions fail or range is reduced.
- Remove transmitter battery and measure cell voltage. If
- If battery voltage is good, open transmitter and inspect battery contacts and internal PCB for corrosion, damage, or water ingress; clean contacts if dirty and re-test.
- Test a known-good spare transmitter: if spare works normally, fault is likely the suspect transmitter. If spare shows same issue, suspect vehicle receiver or interference.
- Inspect RKE/antenna module and corresponding wiring/grounds at the vehicle: check connectors, continuity, and corrosion. Repair any faults and re-test.
- If available, view RSSI/packet data from BCM or receiver with scan tool while operating transmitter to confirm low received signal strength.
- Clear codes, re-test multiple cycles of transmitter operation to verify that B3109 does not reappear.
- If the code persists after replacing battery and confirming transmitter condition, consider replacing the transmitter or diagnosing/repairing the receiver/module or performing BCM software update as per manufacturer service information.
- Document repairs and re-check system operation. If unsure or if module replacement/software update is required, consult dealer-level service information.
Likely causes
- Transmitter battery voltage below expected level (typically
- Battery contacts inside the fob are corroded or bent and not making good contact
- Physical damage or water ingress in the transmitter antenna or PCB
- Antenna/receiver (RKE receiver, keyless entry antenna) has damaged wiring, poor ground, or failed connector
- Nearby RF interference causing retransmissions and low RSSI on the receiver
- BCM misinterpreting legitimate signals due to software glitch
Fault status
Status
Stored when BCM receives three consecutive low-battery messages from the same programmed transmitter. Indicates transmitter is reporting low internal battery or the vehicle is receiving low-level RF from that transmitter; may disable or degrade remote/keyless functions.
Repair difficulty: Easy
Diagnostic time: 0.3-1.0 hours
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Repair manuals
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138
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