U3003
Battery Voltage
The control module detected battery voltage outside its acceptable operating window. Either too low (drained battery, weak charging) or too high (charging system overvoltage).
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: easy
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
Ordered by how often each turns out to be the cause.
- Battery aged or sulfatedCommon
- Alternator regulator fault (over- or undervoltage)Possible
- Gateway module routing CAN messages incorrectlyLess likely
Parts involved
- Battery
- Alternator
- Charging System
U3003 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.