BMW N43/N46 engine: faults and reliability

• N46B20 127-148 hp, indirect injection (2004-2007)

  2004–2007 · 127–148 hp · N46B20A, N46B20O1, N46B20U0, N46B20U1, N46B20U2

  With caution

  Like the rest of the family, it can suffer wear of the timing chain guides and tensioner and of the Valvetronic or VANOS; as it has no direct injection, it is not affected by the injector and NOx sensor failures documented on the N43.^[3][4]

• N46NB20 150-170 hp, revised ECU (2006-2012)

  2006–2012 · 150–170 hp · N46NB20

  With caution

  It shares the risk of chain, Valvetronic and VANOS wear with the rest of the family; as it keeps indirect injection, it does not show the injector and NOx sensor failures specific to the N43.^[3][4][7]

• N43B16 121 hp, 1.6 litres (2007-2011)

  2007–2011 · 121 hp · N43B16

  With caution

  It shares the risk of timing chain wear and, because of its direct injection, the documented failures of the injectors, coils and NOx sensor; as it has no Valvetronic according to English-language Wikipedia, that particular wear does not affect it, although VANOS valve wear does.^[1][3]

• N43B20 121-168 hp, 2.0 litres (2007-2013)

  2007–2013 · 121–168 hp · N43B20

  With caution

  It accumulates all the documented risks of the family: wear of the timing chain, of the Valvetronic and of the VANOS and, because of its direct injection, failures of the injectors, ignition coils and NOx sensor.^[1][3]

Buy: No known serious faults, or they have already been corrected, in this version. With caution: Worth buying if something specific is verified: history, a replaced part or a completed campaign. Avoid: High risk of a serious fault that is hard to check for or prevent.

1. 1Critical severityCommonFrequency: CommonTimingWear and breakage of the timing chain guidesYes: both the N43 and the N46 can stretch the timing chain and wear its plastic guides and tensioner. On the N43, English-language Wikipedia documents that a broken guide can release fragments that block the oil strainer and cause serious damage through lack of lubrication.
2. 2Medium severityCommonFrequency: CommonInjectionInjector, ignition coil and NOx sensor failures (N43)On the direct-injection BMW N43, failures of the injectors, ignition coils (mainly in 2007-2008 units, now rare after a BMW service action) and the NOx sensor of its lean-burn combustion have been documented. The indirect-injection N46 does not have that sensor and does not suffer these failures.
3. 3Medium severityCommonFrequency: CommonIntakeWear of the Valvetronic and the VANOS solenoid valvesOver the years, the eccentric shaft or the actuator motor of the Valvetronic can wear and cause heavy idle fluctuations; the VANOS solenoid valves also fail over time, with similar symptoms and a loss of power. According to English-language Wikipedia, the 1.6-litre N43B16 does not have Valvetronic.
4. 4Medium severityCommonFrequency: CommonLubricationOil leaks and consumption (rocker cover, vacuum pump and valve stem seals)Over the years, the rocker cover gasket and the brake servo vacuum pump gasket start to seep oil on the N43 and N46; on the N46 there are also the valve stem seals, which can cause more noticeable oil consumption than on the N43.

Severity colours: low, medium, high, critical. How we rate them

Manufacturer

BMW

Fuel

Petrol

Displacement

—

Cylinders

4

Fuel system

Naturally aspirated

Injection

Direct injection

Timing

Chain

Power

121–170 hp

Peak torque

210 Nm

Production

2004–2012

Makes

BMW

Technical data^[1][2][5][6]

1. 2004–2007

   N46B20 127-148 hp, indirect injection (2004-2007)

   First relevant generation of the 2.0-litre N46 with indirect injection, Valvetronic and double VANOS; in Europe it powered mainly the BMW 118i, the 318i/320i of the 3 Series E90 and the Z4 2.0i, until the N43 gradually replaced it from 2007.^{[2][8][9][10]}

2. 2006–2012

   N46NB20 150-170 hp, revised ECU (2006-2012)

   Revision of the N46 with a different ECU, which BMW kept in production for several more years in models where the direct-injection N43 was never fitted, such as the BMW X1 sDrive18i and the 520i of the 5 Series E60.^[2][7][11]

3. 2007–2011

   N43B16 121 hp, 1.6 litres (2007-2011)

   1.6-litre version of the N43, with lean-burn direct injection and stratified charge. According to English-language Wikipedia, this variant does not have Valvetronic. It powered the BMW 116i and the 316i.^[1][5][9]

4. 2007–2013

   N43B20 121-168 hp, 2.0 litres (2007-2013)

   2.0-litre version of the N43, with direct injection, which replaced the 2.0 N46 in most European models from 2007: 116i, 118i, 120i, 318i and 320i.^[1][5][8][9]