BMW 3 Series E90 320d N47 2.0d 177bhp — Alternator / Smart Charge System Failure
Modern vehicles use smart charging systems to reduce engine load, but the complex regulators on the alternators frequently fail.
Severity
SevereDIY Difficulty
Moderate
Est. Cost
£250–£450
OBD Codes
P0620P0622Electrics
Typical layout and location for the Electrics assembly.
Symptoms
- Red battery warning light on dashboard
- 'Charging System Fault' message
- Systems shutting down (radio, power steering) as battery depletes
- Car fails to start
Root Cause
The internal voltage regulator or diode pack on the alternator burns out due to heat and age. Occasionally, a slipping auxiliary belt causes the issue.
How To Fix
- Test battery voltage with engine running (should be 13.8V - 14.7V).
- If below 12.5V, replace the alternator.
- Always replace the auxiliary drive belt at the same time.
- Cost: £250-450
Estimated Repair Costs
| Repair Option | Est. Cost (GBP) |
|---|---|
| DIY (parts only) | £100–£180 |
| Independent Garage | £250–£450 |
| Main Dealership | £400–£720 |
Other Faults on This Variant
N47 Timing Chain Failure (Rear of Engine)
CriticalThe BMW N47 diesel engine has a timing chain positioned at the REAR of the engine, against the bulkhead. Chain failure is catastrophic, and repair requires engine removal. This is the most significant known fault in the BMW 3 Series range.
Swirl Flap Failure and Engine Ingestion
CriticalThe N47 intake manifold has metal swirl flaps on actuator rods. When the rods corrode and snap, the flap breaks off and gets ingested into the engine, causing severe internal damage.
EGR Cooler and Valve Failure
ModerateEGR cooler failure on the N47 is common from 70,000 miles. Coolant leaks into the intake manifold and the EGR valve sticks, causing power loss and rough running.
Disclaimer: Repair cost estimates are indicative and based on community data. Always get a quote from a qualified mechanic before proceeding with any repair.