Code
B1513
HUMMER
B — Body
Voltage falls below 10.5 volts with the engine is running
AI status
Completed
Completed
100%
Causes
- Weak or discharged battery
- Failing alternator or voltage regulator
- Loose, corroded or damaged battery terminals/cables
- Poor engine-to-chassis or battery ground connections
- Slipping or broken accessory drive belt
- High electrical load or short/parasite drain
Symptoms
- Battery warning or charge lamp illuminated
- Dim, flickering, or slow headlights and interior lamps
- Slow or hard engine cranking; possible no‑start if voltage falls further
- Intermittent ECU/module faults or resets
- Loss of accessories or erratic electrical behavior
- Possible engine performance issues or limp mode depending on module behavior
What to check
- Scan vehicle for related codes and capture freeze‑frame data
- Measure battery resting voltage (engine off) — should be ≈12.6 V for a healthy battery
- Measure battery voltage while cranking and with engine idling and at ~2000 rpm
- Inspect battery terminals, clamps and cable condition; check for corrosion or looseness
- Check and tension accessory drive belt(s) and inspect for slippage
- Perform charging system output test at the alternator B+ and at the battery
Signal parameters
- Battery resting voltage (engine off): ~12.4–12.7 V expected
- Cranking voltage: typically >9.0 V (varies by temperature)
- Charging system voltage (engine idle): 13.5–14.8 V expected
- Trigger threshold for this code: voltage < 10.5 V while engine running
- AC ripple from alternator: typically
Diagnostic algorithm
- Confirm code and record freeze‑frame data to see RPM/load when low voltage occurred
- Visually inspect battery, terminals, cables, ground straps and alternator connections; clean and tighten as needed
- Measure and record battery voltage (engine off), then during crank, at idle and at ~2000 rpm
- If charging voltage is below specification, test alternator output at the alternator B+ and at the battery; perform a diode/AC ripple check
- Perform voltage drop tests: battery positive to alternator B+ under load, and battery negative to engine block/chassis under load — voltage drops should be minimal (
- Perform a battery load test or CCA test to verify battery health; replace battery if weak or failing
- Check accessory belt tension and condition; replace or adjust if slipping
- If battery and alternator test good, check for parasitic draw with ignition off and fuses removed to isolate circuits
- Inspect and test battery/charging system wiring and any battery current or voltage sensors; repair damaged wiring/connectors
- After repairs, clear codes and road test while monitoring system voltage to confirm condition is resolved
Likely causes
- Battery internal failure (low cold cranking amps)
- Alternator not producing proper charging voltage
- Corroded/loose battery cable or ground strap creating voltage drop
- Faulty voltage sensing/charging circuit wiring or connector
- Accessory drawing excessive current (aftermarket equipment, stuck relay)
Fault status
Status
System detected vehicle voltage below 10.5 V while engine running. Low voltage condition may impair module operation and charging; investigate battery, charging system and wiring.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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