BMW N43 Engine Reliability Guide
The BMW N43 is the UK and European direct-injection 2.0-litre (and 1.6-litre) four-cylinder petrol of 2007 to 2013: 116i, 118i, 120i, 316i, 318i, 320i and 520i. Lean-burn combustion, piezo injectors, a NOx sensor, and the worst reliability record of any BMW four-cylinder petrol. Cheap cars for a reason.
Quick verdict
Only buy an N43 with a documented injector set and a smooth cold idle. Piezo injectors fail from 40,000 miles at £1,200 to £2,000 a set, the NOx sensor fails repeatedly at £350 to £700, the timing chain needs watching and the high-pressure pump follows. E90 316i, 318i and 320i and E87 116i to 120i of 2007 to 2011 are the cheapest BMWs of their age because of this engine. ULEZ-compliant, which is the one thing in its favour.
What is the BMW N43?
Most N43 cars in UK classifieds are E90 / E91 318i and 320i and E87 / E81 118i and 120i from 2008 to 2011 at £1,500 to £4,500, often with a rough idle the seller describes as normal. It is not. BMW quietly put the port-injection N46 back into the 316i and 318i in 2010 to 2012, so late cars may be the better engine; check the VIN or let Bimmer.AI identify it from the reg.
| Full engine code | N43B20 |
|---|---|
| Configuration | I4 naturally aspirated petrol, direct injection (piezo injectors), lean-burn, UK/EU market only; 1.6 N43B16 in the 116i |
| Production years | 2007-2013 |
| Applicable chassis | E81, E82, E87, E88, E90, E91, E92, E93, E60, E61 |
| Badge names | 116i, 118i, 120i, 316i, 318i, 320i, 520i |
| Real-world UK MPG | 33 to 42 mpg combined, 42 to 48 mpg motorway |
| Emissions / ULEZ | Euro 6, ULEZ-compliant |
| Successor | N13 (1.6 turbo), N20, and N46 reintroduced in 316i/318i |
| Reliability score | 4 / 10 (Bimmer.AI internal) |
Common problems
Every failure mode below is based on UK DVSA/recall data, BMW press archives, and observed patterns across independent specialist maintenance schedules. Cost ranges are indicative UK figures.
| Failure mode | Severity | Frequency | Typical onset | UK repair range |
|---|---|---|---|---|
| Piezo injector failure | Serious | Very common | 40 to 110k mi | £1,200 to £2,000 |
| NOx sensor failure | Moderate | Very common | 50 to 100k mi | £350 to £700 |
| Timing chain guide and tensioner wear | Serious | Common | 70 to 130k mi | £800 to £1,400 |
| High-pressure fuel pump failure | Serious | Common | 60 to 120k mi | £500 to £900 |
| Valvetronic eccentric shaft sensor failure | Moderate | Common | 70 to 130k mi | £300 to £600 |
| Ignition coil and spark plug misfires | Mild | Common | 40 to 100k mi | £100 to £300 |
Piezo injector failure
- Cold-start misfire and rough idle that clears when warm
- Engine warning light with cylinder-specific misfire codes
- Fuel smell and fuel-diluted oil
- Stumble and hesitation on light throttle
What to do about it: Insist on receipts for a matched set of latest-index injectors with coding. A smooth-running-values readout at viewing identifies weak cylinders.
If ignored: Bore wash and catalyst damage, £1,000 or more on top.
UK repair exposure: £1,200 to £2,000.
Recall / TSB: BMW ran an extended injector warranty (typically 10 years or 120,000 miles); most cars are now outside it.
Additional notes: £300 to £500 per injector fitted and coded; four is £1,200 to £2,000. On a £3,000 car that is the whole decision.
NOx sensor failure
- Engine warning light
- Rough idle and hesitation as the engine leaves lean mode
- Noticeably worse fuel economy
What to do about it: Replace at first fault. Check whether it has been coded out by a previous owner.
If ignored: Higher fuel bills, MOT emissions risk. A tired NOx storage catalyst adds £1,000 or more.
UK repair exposure: £350 to £700.
Timing chain guide and tensioner wear
- Rattle on cold start
- Chain noise at idle
- Cam and crank correlation codes
What to do about it: Tensioner first, full chain kit if guides are worn. Front-mounted chain.
If ignored: Chain jump and valve damage.
UK repair exposure: £800 to £1,400.
High-pressure fuel pump failure
- Long cranking
- Hesitation under load
- Low rail pressure codes
What to do about it: None practical; budget for it on high-mileage cars.
If ignored: Eventual no-start.
UK repair exposure: £500 to £900.
Valvetronic eccentric shaft sensor failure
- Rough idle and stalling
- Valvetronic fault codes
- Limp mode
What to do about it: Replace with a valve cover gasket job.
If ignored: Stalling and limp mode.
UK repair exposure: £300 to £600.
Ignition coil and spark plug misfires
- Misfire codes
- Stutter under load
What to do about it: Plugs every 40,000 miles; rule coils out before condemning injectors.
If ignored: Catalyst damage.
UK repair exposure: £100 to £300.
Preventative maintenance schedule
UK independent specialist consensus, typically more cautious than BMW's factory service intervals, especially around oil and timing components.
| Task | Interval | Typical cost | Fix |
|---|---|---|---|
| Engine oil + filter (BMW LL-01) | Every 7,500 mi | £70 to £120 | DIY |
| Spark plugs (4) Direct injection: shorter interval | Every 40,000 mi | £80 to £150 | DIY |
| Air filter | Every 30,000 mi | £25 to £45 | DIY |
| Coolant | Every 60,000 mi | £100 to £160 | Specialist |
| Brake fluid | Every 24,000 mi | £60 to £100 | Specialist |
| Injector health check (smooth-running values) | Every 20,000 mi | £60 to £120 | Specialist |
| Timing chain tensioner check | At 80,000 mi | £100 to £200 | Specialist |
Long-term verdict
The engine that gave BMW's UK four-cylinder petrols a bad name. Lean-burn direct injection means expensive piezo injectors, a NOx sensor that fails repeatedly and a timing chain that also needs watching. E90 316i, 318i and 320i and E87 116i to 120i of 2007 to 2011 are cheap for a reason. Only buy one with a documented injector set and a smooth cold idle. ULEZ-compliant.
Buy, negotiate, or walk away
Buy
All four injectors replaced with a specialist invoice, NOx sensor replaced within 40,000 miles, chain quiet on a cold start, HPFP healthy (no long crank), Valvetronic sensor fault-free.
Negotiate
No injector history past 50,000 miles (£1,200 to £2,000), active NOx fault (£350 to £700), cold-start rattle with no chain history (£800 to £1,400).
Walk away
Rough idle plus misfire codes plus no injector history, or long cranking with a stumble, or a rattle that lasts. The car is cheap because it is.
Check a specific N43 listing
Paste any BMW N43 listing, VIN, or registration. Bimmer.AI returns a N43-specific buyer report in 30 seconds.
Run a Bimmer.AI buyer report →Bimmer.AI is designed to help you identify BMW-specific buyer risks before you travel, negotiate, or pay for an inspection. It does not replace a physical inspection by a qualified mechanic, a legal vehicle-history check (e.g. HPI Check), or independent verification of finance, stolen, or write-off status. Repair-cost ranges are indicative UK figures that vary by region, specialist, parts supply, and labour rates.
Frequently asked questions
Why is the BMW N43 engine so unreliable?
Lean-burn direct injection. To run stratified-charge lean mixtures the N43 uses piezo injectors, a NOx sensor and a high-pressure fuel pump, all of which proved fragile: injectors from 40,000 miles (£1,200 to £2,000 a set), NOx sensors repeatedly (£350 to £700), the HPFP at £500 to £900. Add a timing chain that wears and a Valvetronic sensor that fails and the engine scores 4 out of 10.
Which BMWs have the N43?
UK and European four-cylinder petrols from 2007 to 2013: E81 / E87 / E82 / E88 116i (1.6 N43B16), 118i and 120i, E90 / E91 / E92 / E93 316i, 318i and 320i, and E60 / E61 520i. North American cars did not get it. From 2010 to 2012 the 316i and 318i reverted to the port-injection N46, and from 2011 the N13 turbo and N20 replaced it.
How do I tell an N43 from an N46?
The N43 has a high-pressure fuel pump on the side of the cylinder head and a metal fuel rail with injector wiring; the N46 has a plain plastic intake manifold and port injectors under it. The VIN decodes it definitively (N43 cars carry a different engine code in the build sheet) and Bimmer.AI reports it from the reg. On a test drive, the N43's cold idle is the giveaway when the injectors are tired.
Is the N43 ULEZ-compliant?
Yes. All N43 cars are Euro 5 petrol and inside the ULEZ standard, which is why London buyers meet so many of them at low prices. The engine's reliability, not its emissions, is the problem.