P3802high severityPowertrain
48V Belt Starter-Generator Performance
on 2020 Mazda Mazda3 2.5L I4 · FWD
What this code means
The belt-driven starter-generator (BSG) is not producing expected torque output for engine starting, boost assist, or energy recovery.
Symptoms
- Slow engine cranking
- No electric torque assist
- Weak regenerative braking
- Increased fuel consumption
- Belt squeal during start
- Vibration during BSG operation
Common causes
- BSG internal fault
- Drive belt slip
- Belt tensioner wear
- BSG bearing failure
- Inverter module fault
Diagnostic steps
- Check BSG torque output via scan tool
- Inspect drive belt condition and tension
- Listen for BSG bearing noise
- Test BSG inverter module
- Monitor BSG temperature during operation
Repair notes
Replace BSG unit if internal fault confirmed. Replace drive belt and tensioner if slipping. BSG and belt are a common service item together.
Other Powertrain codes on this vehicle
P0001
Fuel Volume Regulator Control Circuit/Open
P0002
Fuel Volume Regulator Control Circuit Range/Performance
P0003
Fuel Volume Regulator Control Circuit Low
P0004
Fuel Volume Regulator Control Circuit High
P0010
Intake Camshaft Position Actuator Circuit/Open Bank 1
P0011
Intake Camshaft Position Timing Over-Advanced Bank 1
P0012
Intake Camshaft Position Timing Over-Retarded Bank 1
P0013
Exhaust Camshaft Position Actuator Circuit/Open Bank 1
P0014
Exhaust Camshaft Position Timing Over-Advanced Bank 1
P0015
Exhaust Camshaft Position Timing Over-Retarded Bank 1