Code
B1981
HUMMER
B — Body
Battery Voltage Low
AI status
Completed
Completed
100%
Causes
- Weak or discharged battery
- Poor battery terminal or ground connections
- Faulty charging system (alternator/regulator)
- Parasitic electrical drain
- Damaged battery cable or connector
- Corroded or blown fuse/fusible link
Symptoms
- Illuminated battery or charging system warning lamp
- Multiple electrical accessories erratic or non-functional
- Difficulty starting or slow cranking
- Stored or active communication and body control DTCs
- Unexpected module resets or limp-home behavior
- Dim headlights or interior lights
What to check
- Visual inspection of battery for corrosion, cracks, or leaks
- Measure battery resting voltage (key off) with a quality multimeter
- Measure battery voltage while cranking and with engine running
- Test charging output at battery and at alternator terminals
- Inspect and clean battery terminals, cable ends, and ground straps
- Check main fuses, fusible links, and battery feed circuits to BCM
Signal parameters
- Battery resting voltage (key off): ~12.4–12.8 V (healthy charged battery)
- Minimum acceptable cranking voltage: typically >9.5 V (varies by vehicle)
- Charging system voltage (engine running): ~13.5–14.8 V
- Low-voltage fault threshold: often triggered when voltage falls below ~9–11 V (manufacturer-specific)
- Alternator ripple/noise: low; excessive AC ripple indicates regulator/diode issues
Diagnostic algorithm
- Record customer complaint and all stored DTCs including freeze-frame data.
- Perform a visual inspection of the battery, cables, terminals, ground straps and main fuses for damage or corrosion.
- With a fully charged known-good battery or after confirming battery resting voltage, measure key-off battery voltage. If below ~12.2 V, charge battery and re-test or perform a conductance/CCA test to assess battery condition.
- Start engine and measure charging voltage at battery positive/negative. Confirm charging voltage is within ~13.5–14.8 V. If low, test alternator output and inspect alternator ground and connections.
- If voltage drops during cranking below acceptable cranking voltage, perform load/cranking test and retest battery under load. Replace battery if it fails conductance/CCA or load test.
- If charging system is good and battery is healthy, perform a parasitic draw test to identify excessive current drain with ignition off. Isolate circuits by removing fuses/relays as needed.
- Inspect and backprobe BCM power and ground circuits; verify stable supply voltage and good grounds. Repair any damaged wiring, corroded connectors, or poor grounds.
- Clear the code and test drive or cycle ignition to confirm code does not return. If code returns after repairs, pursue module-level diagnostics (voltage sense circuit, BCM) per manufacturer procedures.
- If wiring, battery and charging system are confirmed good and low-voltage condition persists tied to the BCM, consider module replacement only after consulting service information and verifying programming/calibration requirements.
Likely causes
- Battery state-of-charge below acceptable threshold or battery failing under load
- High-resistance or loose negative/positive battery terminals or ground strap
- Alternator not producing adequate charging voltage at idle or load
- Accessory or short drawing current with ignition off (parasitic drain)
- Damaged wiring to BCM or poor voltage sense circuit connection
- Blown main fuse or fusible link supplying BCM
Fault status
Status
Body module detected battery voltage below expected threshold. May impact multiple electrical systems; check battery, charging system, connections and BCM power/ground circuits.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
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Code
B1981
Other
B — Body
Memory Off Switch Circuit Short to Battery
AI status
Completed
Completed
100%
Causes
- Weak or discharged battery
- Poor battery terminal or ground connections
- Faulty charging system (alternator/regulator)
- Parasitic electrical drain
- Damaged battery cable or connector
- Corroded or blown fuse/fusible link
Symptoms
- Illuminated battery or charging system warning lamp
- Multiple electrical accessories erratic or non-functional
- Difficulty starting or slow cranking
- Stored or active communication and body control DTCs
- Unexpected module resets or limp-home behavior
- Dim headlights or interior lights
What to check
- Visual inspection of battery for corrosion, cracks, or leaks
- Measure battery resting voltage (key off) with a quality multimeter
- Measure battery voltage while cranking and with engine running
- Test charging output at battery and at alternator terminals
- Inspect and clean battery terminals, cable ends, and ground straps
- Check main fuses, fusible links, and battery feed circuits to BCM
Signal parameters
- Battery resting voltage (key off): ~12.4–12.8 V (healthy charged battery)
- Minimum acceptable cranking voltage: typically >9.5 V (varies by vehicle)
- Charging system voltage (engine running): ~13.5–14.8 V
- Low-voltage fault threshold: often triggered when voltage falls below ~9–11 V (manufacturer-specific)
- Alternator ripple/noise: low; excessive AC ripple indicates regulator/diode issues
Diagnostic algorithm
- Record customer complaint and all stored DTCs including freeze-frame data.
- Perform a visual inspection of the battery, cables, terminals, ground straps and main fuses for damage or corrosion.
- With a fully charged known-good battery or after confirming battery resting voltage, measure key-off battery voltage. If below ~12.2 V, charge battery and re-test or perform a conductance/CCA test to assess battery condition.
- Start engine and measure charging voltage at battery positive/negative. Confirm charging voltage is within ~13.5–14.8 V. If low, test alternator output and inspect alternator ground and connections.
- If voltage drops during cranking below acceptable cranking voltage, perform load/cranking test and retest battery under load. Replace battery if it fails conductance/CCA or load test.
- If charging system is good and battery is healthy, perform a parasitic draw test to identify excessive current drain with ignition off. Isolate circuits by removing fuses/relays as needed.
- Inspect and backprobe BCM power and ground circuits; verify stable supply voltage and good grounds. Repair any damaged wiring, corroded connectors, or poor grounds.
- Clear the code and test drive or cycle ignition to confirm code does not return. If code returns after repairs, pursue module-level diagnostics (voltage sense circuit, BCM) per manufacturer procedures.
- If wiring, battery and charging system are confirmed good and low-voltage condition persists tied to the BCM, consider module replacement only after consulting service information and verifying programming/calibration requirements.
Likely causes
- Battery state-of-charge below acceptable threshold or battery failing under load
- High-resistance or loose negative/positive battery terminals or ground strap
- Alternator not producing adequate charging voltage at idle or load
- Accessory or short drawing current with ignition off (parasitic drain)
- Damaged wiring to BCM or poor voltage sense circuit connection
- Blown main fuse or fusible link supplying BCM
Fault status
Status
Body module detected battery voltage below expected threshold. May impact multiple electrical systems; check battery, charging system, connections and BCM power/ground circuits.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Similar codes
Repair manuals
Brands with available manuals
6,959
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