Battery Voltage High During Key On
Indicates that the battery voltage is higher than expected during ignition key-on.
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)
When you turn the key, the computer checks the battery voltage and sees it's really high, more than 16 volts, which can be caused by a bad regulator or poor connections.
What the computer is actually seeing
The computer is monitoring voltage in the system when the key is turned on and expects values between 12.0 to 15.5 volts, anything above 16 volts triggers this code.
What a healthy reading looks like
Expected voltage during key-on is between 12.0 and 15.5 volts; over 16 volts triggers the B1399 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.
- 1Check battery voltage with a multimeter. It should be between 12.0 to 15.5 volts. If over 16 volts, proceed to next step.
- 2Inspect the battery terminals for corrosion or loose connections. Clean and tighten if necessary; recheck voltage.
- 3Measure the alternator output voltage with the engine running. Should be between 13.5 to 14.5 volts. If higher, replace the regulator or alternator as needed.
- 4Inspect all wiring between the battery, alternator, and engine control module for any signs of damage or high resistance.
Common causes
- Faulty voltage regulator
- Bad battery connections
- A failing alternator
- Corroded wiring
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It may not be safe; high voltage can damage components. Fix it as soon as possible.
Will this code come back after clearing it?
If the underlying issue isn't fixed, it will likely return after driving a short distance.
Why does this code pair with B1379 or B1380?
These codes indicate related issues in the battery or charging systems, reflecting problems with voltage regulation.
Working a real vehicle right now?
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