The mid-range petrol in BMW's first rear-wheel-drive hatchback. The 120i offers a rewarding driving experience with adequate power for daily use. Two engines were fitted: the N46 with Valvetronic (2004-2007) and the direct-injection N43 (2007-2011). Both are 2.0-litre four-cylinders but have distinctly different weak points that buyers need to understand before purchasing.
Engaging rear-wheel-drive dynamics
Widely available, affordable parts
Engine-specific weak points (both)
Rear subframe prone to corrosion
Buy if: You find a well-maintained example with complete service history and can identify whether it has the N46 or N43 engine to understand its specific risks.
Avoid if: You hear cold-start rattling, see warning lights on the dashboard, or the service history is incomplete.
Expected Annual Maintenance Costs
Common Problems
Plastic chain guides deteriorate and tensioner bleeds off pressure, causing cold-start rattle and risk of engine damage · more· less
Both the N46 and N43 engines use a timing chain with plastic guides that become brittle from heat cycling and degrade over time. The tensioner bleeds off oil pressure overnight, resulting in a metallic rattling noise for 1-30 seconds on cold start. This typically surfaces between 80,000 and 130,000 km. On the N43, the problem is more severe: fractured guide debris can fall into the oil pan and block the oil pump strainer, causing oil starvation and catastrophic engine seizure. BMW ran a testing campaign for N43 timing chains but did not replace them preventively. Independent specialists charge approximately €800-1,200 for a complete chain, guides, tensioner, and sprocket replacement. If the chain has skipped teeth or caused engine damage, a replacement engine costs €2,500-3,500 installed.
Valvetronic system components degrade causing rough idle, reduced power, and engine warning lights · more· less
The N46 engine (2004-2007) uses Valvetronic variable valve lift, controlled by an electric motor and eccentric shaft. The eccentric shaft sensor can leak oil past its seal, corrupting the electrical connector and signal. The Valvetronic motor itself can overheat, and the eccentric shaft develops wear spots that cause binding. Return springs are also known to break. Symptoms include erratic idle, reduced power, and engine management warning lights. The eccentric shaft sensor costs approximately €100-150 for the part, with about 2-3 hours labor (€200-400 total). If the motor or eccentric shaft needs replacement, costs reach €600-1,500 at an independent specialist due to extensive labor. This issue typically manifests between 100,000 and 150,000 km. The N43 engine (2007-2011) does not use Valvetronic.
Piezo direct injectors fail causing misfires, rough running, and cascading ignition coil damage · more· less
The N43 engine uses high-pressure piezo direct injectors that are expensive and failure-prone. BMW revised the injectors at least eleven times. When an injector fails, it causes misfires that foul the spark plugs, which then overload and damage the ignition coils. This creates a cascade of failures that makes diagnosis confusing. Additionally, leaking injectors wash the oil film from cylinder walls, leading to premature bore wear. New OEM injectors cost approximately €200-300 each, plus ECU coding. Replacing all four injectors with new plugs and coils at an independent specialist runs €800-1,500. This issue typically appears between 80,000 and 150,000 km. The N46 engine uses conventional port injection and is not affected.
NOx sensor degrades causing unstable idle, increased fuel consumption, and emission fault codes · more· less
The N43 engine has a NOx sensor for its lean-burn direct injection system. This sensor is prone to failure, causing unstable engine speed, increased fuel consumption, and persistent fault codes. Symptoms include hesitation on acceleration and rough idle. The sensor is manufactured by Continental and OEM replacement is recommended, as aftermarket sensors often do not work correctly. The sensor costs approximately €300-400, with about 1 hour labor. Some owners use a NOx emulator (€100-150) as a workaround, but this disables the lean-burn function and may not pass emissions testing. Average sensor lifespan is approximately 150,000 km. This issue does not affect the N46 engine.
Hardened valve stem seals cause excessive oil consumption and blue smoke on startup · more· less
The N46 engine operates at high coolant temperatures (105°C), which causes the rubber valve stem seals to harden and lose their sealing ability over time. Symptoms include light blue smoke on startup after the car has been sitting, oil consumption exceeding 1 litre per 2,000 km, and fouled spark plugs. This typically develops between 120,000 and 180,000 km. BMW released redesigned stem seals that are more heat-resistant. Replacement requires removal of the camshafts and is labor-intensive. Independent specialists charge €800-1,200 for the job, while BMW dealers quote €1,500-2,000. Using quality synthetic oil (BMW LL-01 specification) and avoiding extended oil change intervals helps delay onset.
Gasket hardens with age causing oil leaks onto exhaust manifold and ignition components · more· less
The valve cover gasket on both N46 and N43 engines hardens and shrinks over time, allowing oil to seep out. Oil can drip onto the exhaust manifold, creating a burning smell and smoke, or pool around the spark plug wells, contaminating the ignition coils and accelerating their failure. The gasket itself costs €30-60, but the job requires 2-3 hours of labor. Total cost at an independent shop is €200-400, while BMW dealers charge €400-600. On the N46, the valve cover also houses the crankcase ventilation (CCV) system. If the CCV diaphragm fails, the entire valve cover may need replacing at €200-400 for the part alone. This is a near-certainty on cars over 10 years old.
Expansion tank cracks, thermostat housing leaks, and water pump impeller can break · more· less
The E87 cooling system uses plastic components that become brittle with age and heat cycling. The expansion tank develops hairline cracks and can burst without warning, causing rapid coolant loss and overheating. The electrically controlled thermostat can fail open or closed. The mechanical water pump uses a plastic impeller that can erode or break. Individual repairs are relatively affordable (expansion tank €30-50, thermostat €60-80, water pump €100-150), but a complete cooling system overhaul including all hoses runs €400-700 at an independent shop. Many experienced BMW owners replace the entire cooling system preventively around 100,000 km. By that mileage, at least one component will have needed attention.
Rear subframe rusts from stone chips and road salt, can fail inspection if severe · more· less
The E87 rear subframe is susceptible to corrosion on its lower edges where it is exposed to road spray, stone chips, and salt. This is well documented across the E87 community, with some owners reporting subframes corroded so severely they cracked, potentially damaging brake lines. Finding a rust-free replacement is increasingly difficult as most used subframes are also corroded. Surface treatment with wire brushing and rust-inhibiting coatings costs €300-500 professionally. If the subframe needs replacement, a used unit plus fitting costs €800-1,200. Cars from coastal areas or regions with heavy road salt use are most affected. Preventive underbody wax treatment every two years significantly slows progression.
Water enters boot through rear light seals and vent panels, corroding the PDC module and causing cascading electrical faults · more· less
The E87 boot area is prone to water ingress through the rectangular vent panels behind the trim and through poorly sealed rear light housings. Water accumulates and soaks the PDC (parking distance control) module housed in the right side of the boot. A waterlogged PDC module sends corrupted signals on the CAN bus network, causing cascading electrical faults including complete instrument cluster failure (speedo, rev counter, temperature gauge all go dead), random warning lights, and central locking issues. DIY resealing of vents and light housings costs €10-20. If the PDC module is damaged by corrosion, replacement costs €150-300. If other modules on the CAN bus are affected, diagnosis and repair can reach €500.
Engine choice determines your ownership experience
The BMW 120i E87's reliability depends heavily on which engine is fitted. The N46 (2004-2007) uses port injection and Valvetronic variable valve lift, making it mechanically simpler than the N43 but adding Valvetronic motor, eccentric shaft, and valve stem seal concerns at higher mileage. The N43 (2007-2011) replaced Valvetronic with direct injection, introducing expensive piezo injectors, a failure-prone NOx sensor, and more aggressive timing chain failure modes. Both variants share oil leak tendencies, cooling system fragility, and E87-specific body issues including rear subframe corrosion and boot water ingress. With regular oil changes (every 10,000-15,000 km rather than BMW's extended interval) and proactive cooling system maintenance, both engines can deliver reliable service well beyond 200,000 km.
Recalls and Technical Service Bulletins
Takata airbag inflator (various production dates)
Critical - verify completed
Timing chain testing campaign (N43 engines, 2007-2011)
Verify completed
Fuel pump relay (certain 2006-2008 models)
Verify completed
Contact a BMW dealer with the VIN to verify all recalls and service campaigns have been completed. The Takata airbag recall is a critical safety issue. The N43 timing chain testing campaign only checks for existing stretch and does not preventively replace the chain — ask specifically whether any chain work was done.
Warranty Status
Factory warranty (2 years)
Expired on all E87 models
Rust perforation warranty (12 years)
Expired on all E87 models
All BMW 120i E87 models are well outside their original 2-year factory warranty and 12-year rust perforation warranty. Third-party warranty providers may offer coverage but typically exclude known problem areas like timing chains, Valvetronic components, and injectors. Extended warranty is rarely cost-effective on cars of this age and value.
This report is for informational purposes only and does not constitute professional advice. Estimates may be inaccurate. Always have a qualified specialist inspect the vehicle before purchase. We accept no liability for decisions made based on this information.