Body Control Module - Battery Voltage Too Low
Indicates that the body control module is detecting low battery voltage.
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What it means (plain English)
The body control module (BCM) monitors the vehicle's battery voltage. If it drops below a certain threshold, usually around 9 volts, it triggers the B1599 code to warn that the system isn't getting enough power to operate correctly.
What the computer is actually seeing
The BCM monitors voltage levels in real time, comparing them to programmed thresholds. When voltage falls below about 9 volts for more than 60 seconds, a fault is logged.
What a healthy reading looks like
Normal battery voltage should be between 12.4 to 14.7 volts when the engine is running. Under load, like when using accessories, voltage should not drop below 9 volts for extended periods.
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 the battery voltage with a multimeter; it should be above 12.4 volts. If not, recharge or replace the battery.
- 2Inspect battery terminals for corrosion or loose connections; clean and secure as needed.
- 3Start the engine and recheck voltage; it should be between 13.5 to 14.7 volts with the engine running.
- 4If voltage is low at idle, check the alternator output; it should be above 13.5 volts. If it's low, test or replace the alternator.
- 5Inspect wiring and connectors from the alternator to the battery for shorts or breaks; repair as necessary.
- 6If all checks are fine but the code persists, consider testing or replacing the BCM.
Common causes
- Weak battery
- Bad alternator
- Corroded battery terminals
- Shorts in wiring
- BCM failure
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's usually drivable, but you may face electrical issues and should fix it soon.
Will the code come back after I clear it?
If the underlying issue isn't fixed, yes, the code will reappear.
What if my voltage checks out but the code is still present?
There may be an internal BCM issue; further diagnostics or replacement may be needed.
Working a real vehicle right now?
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