P3803high severityPowertrain
48V DC-DC Converter (48V to 12V) Fault
on 2018 Mazda Mazda3 2.5L I4 · FWD
What this code means
The DC-DC converter that steps down 48V to charge the 12V system and battery has a fault. In 48V systems, this converter often replaces the traditional alternator.
Symptoms
- 12V battery not charging
- Electrical accessories dimming
- 12V battery warning light
- Vehicle may not restart
- Multiple low-voltage warnings
- Infotainment resets
Common causes
- DC-DC converter internal failure
- 48V input voltage out of range
- 12V output regulation failure
- Cooling system issue for converter
- Communication fault with BMS
Diagnostic steps
- Measure DC-DC converter 12V output
- Check 48V input voltage
- Monitor 12V battery charge state
- Test converter cooling fan
- Read converter internal fault codes
Repair notes
Replace 48V to 12V DC-DC converter. Charge or replace 12V battery if damaged by undervoltage.
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P0015
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