Battery Voltage High
The battery voltage exceeds the 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 is supplying a voltage higher than 16 volts, which is too high for the vehicle's electrical system. This can happen because of a faulty alternator or incorrect battery issues.
What the computer is actually seeing
The vehicle's computer monitors the battery voltage through a sensor. When it senses voltage above 16 volts for a certain period (usually over 5 seconds), it triggers the B138A code.
What a healthy reading looks like
Normal battery voltage should be between 12.6 and 14.4 volts at idle; above 16 volts indicates a problem during charging.
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. Verify battery voltage with a multimeter; should be between 12.6 - 14.4 volts.
- 22. Check for loose or corroded battery connections and clean them if found.
- 33. Inspect the alternator output while the engine is running; it should not exceed 14.5 volts under load.
- 44. Test the battery with a load tester; if it fails, replace it.
- 55. If the alternator is faulty, replace it and clear the code; retest the system after replacement.
Common causes
- Faulty alternator
- Bad battery
- Loose or corroded connections
- Incorrectly rated battery for the system
- Voltage regulator failure
Typical repair cost
$$-$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not advisable to drive with this code; high voltage can damage electronic components.
Will the code come back after clearing it?
If the underlying issue isn't resolved, the code may return.
Could this be related to recent battery service?
Yes, incorrect installation or using the wrong battery can trigger this issue.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →