Battery Voltage Low (Under Voltage)
The battery voltage is below normal operating range.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The battery isn't supplying enough voltage, causing issues with starting the vehicle and powering electrical systems.
What the computer is actually seeing
The body control module (BCM) monitors battery voltage through its voltage reference pin. If the voltage drops below a set threshold (usually around 10.5V), this code sets.
What a healthy reading looks like
Normal battery voltage should be between 12.4V and 12.8V. Below 10.5V will trigger the B1403 code.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check battery voltage with a multimeter. Expected: 12.4V to 12.8V. - If below 12.4V, charge or replace the battery. - If above 12.4V, proceed to step 2.
- 22. Inspect battery connections and terminals for corrosion or looseness. - Clean and tighten terminals if necessary. - If connections are good, proceed to step 3.
- 33. Start the engine and measure voltage at the battery with the engine running. Expected: 13.5V to 14.5V. - If below 13.5V, check the alternator output and connections. - If within range, proceed to step 4.
- 44. Check for any unusual electrical loads (aftermarket devices, lights, etc.). Disconnect unnecessary loads and monitor the system.
- 55. If issues persist, inspect wiring between the battery, alternator, and BCM for damage.
Common causes
- Weak or discharged battery
- Corroded battery terminals
- Faulty alternator
- Wiring issues in the charging system
- Excessive electrical load on the system
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not recommended as it can lead to starting issues or loss of power for critical systems.
Will this code come back after clearing?
Yes, if the underlying issue isn't resolved — like a bad battery or alternator.
Why does this code appear with other codes?
Issues with the battery or charging system can affect multiple modules and sensors, causing related codes to set.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
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