BMW 3 Series E90 320d N47 2.0d 177bhp — Piezo Injector Failure
The N47 relies on Bosch piezoelectric injectors. These wear internally, causing over-fuelling, rough idling, and potentially piston damage if they stick open.
Severity
SevereDIY Difficulty
Professional Only
Est. Cost
£300–£1200
OBD Codes
4B104B11Injectors
Typical layout and location for the Injectors assembly.
Symptoms
- Rough, shaky idle especially when cold
- Strong smell of unburnt diesel from exhaust
- Increased fuel consumption
- Engine vibration under light load
Root Cause
Internal wear of the injector nozzle and control valve. Contaminated diesel accelerates wear. The piezoelectric crystals can also degrade electrically.
How To Fix
- Run smooth running balance test via diagnostics
- Perform leak-off test to confirm faulty injectors
- Replace faulty injectors (Bosch remanufactured recommended)
- New injectors MUST be coded (IMA code) to the DDE/ECU
- Cost: £250-350 per injector fitted
Estimated Repair Costs
| Repair Option | Est. Cost (GBP) |
|---|---|
| DIY (parts only) | £120–£480 |
| Independent Garage | £300–£1200 |
| Main Dealership | £480–£1920 |
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.