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there's a few small issues with the engine but its not that bad; points to note are:
1. Engine knocking. This problem is mainly connected with timing chain tensioner which should be checked. At the same time timing chains are not as reliable as you can expect. They also need replacement every 60,000 miles (100,000 km) of mileage due to the fact that they stretch. It can result in timing chain jumping. this is the main complaint with the engine but as long as you're aware of it its not an issue
2. Vibration. In the majority of cases this problem is connected with Vanos system. If you want to get rid of this problem you must have your Vanos cleaned.
At the same time BMW N45 engine is prone to pinking. That is why you are supposed to use gasoline and motor oil of high quality only. You should take it rather seriously and buy only recommended by BMW brand oil.
28-11-2006 R/2006/207 BMW1 SERIES AND 3 SERIES possible loss of braking power assistance build dates 04-03-2006 to 14-03-2006
May 2007 TSB: SI B 61 28 06 General Electrical Systems May 2007 Technical Service. This Service Information bulletin supersedes S.I. B61 28 06 dated January 2006. [NEW] designates changes to this revision SUBJECT: ELV Warning in Instrument Cluster MODEL E90, E91, E92 (3 Series) E60, E61 (5 Series) E63, E64 (6 Series). SITUATION: The ELV (Electronic Steering Lock) check control warning illuminates in the instrument cluster and in some cases, engine start is inhibited. Diagnostics reveals fault code A0AA in the CAS (Car Access System) and prompts a control unit replacement. CAUSE: Low voltages in the vehicle electrical system when cranking/starting the engine. PROCEDURE [NEW]: This problem has been integrated into DIS diagnostics. Follow diagnostics and relevant test plan using DIS V49.0 or later.
April 2008: Recall on official fitted folding towbar. Cables chafe and cause a general electrical problem. 22-10-2008: TSB recall notice to keepers of post September 2007 325i models: "As part of our ongoing quality analysis at BMW it has been established that the injector of the fuel injector system might fail causing poor engine and lack of power on your vehicle."
22-10-2008: TSB recall notice to keepers of post September 2007 325i models: "As part of our ongoing quality analysis at BMW it has been established that the injector of the fuel injector system might fail causing poor engine and lack of power on your vehicle."
30-06-2009 R/2009/065 BMW 1 Series & 3 Series front side airbag or seat belt tensioner may not operate correctly build dates 23/05/2008 - 21/07/2008
26-10-2010: Woodcliff Lake, NJ: BMW of North America has notified the US Environmental Protection Agency (EPA) of its intent to conduct a voluntary recall of some model year 2007-2010 BMWs equipped with twin-turbo inline six-cylinder engines, all of which feature BMW’s High Precision Injection direct fuel injection system. It has also asked for approval from the California Air Resources Board to conduct this action. Affected vehicles may experience a failure of the high-pressure fuel pump. Symptoms include long-crank engine starting times along with the illumination of the “Service Engine Soon” light. In certain cases, the driver may experience reduced engine performance in a Safe Mode accompanied by a tone and the illumination of the “Engine Malfunction” light. Based on the individual service history of the vehicle, the action will entail replacement of the high-pressure fuel pump and/or a software update. Approximately 130,000 vehicles are potentially affected with about 40,000 expected to require a new high pressure fuel pump. Affected BMW models include, MY 2007–2010 335i models, MY 2008–2010 135i, 535i and X6 xDrive35i Sports Activity Coupes, MY 2009 – 2010 Z4 Roadster sDrive35i. In a separate action, BMW has notified the National Highway Traffic Safety Administration (NHTSA) that it will voluntarily recall approximately 20,800 MY 2008 X5 Sports Activity Vehicles equipped with normally-aspirated inline six-cylinder engines to replace the low-pressure fuel pump. In this case, should the fuel pump experience a failure, the engine will stop running and the driver will lose power assist for the steering and brakes although both the steering and the brakes remain operational.
15-4-2014: Worldwide recall of 489,000 BMW cars with six-cylinder 2.5 and 3.0 litre petrol engines of which less than 3,000 are in the UK. These are: N51 (1991-1995), N52 (from 2005) and the N55 6-cylinder petrol turbo (from 2009). The screws for the housing of the adjustment unit of the variable camshaft timing (Vanos) for the intake and exhaust camshafts could potentially become loose or break. An engine warning lamp ‘should ’ appear in such circumstances, but if drivers experience any loss of power they should contact their BMW dealer immediately.
28-7-2014: R/2014/068 BMW 1, 3, 4, 5, 6, X1, X3, X5, Z4 Build Dates 1-9-2009 to 30-11-2011: Concern : ENGINE EMERGENCY MODE MAY BE ACTIVATED DURING DRIVING Description : The screws retaining the variable camshaft timing (VANOS) housing may loosen and under certain circumstances the heads may break off. This can lead to the VANOS leaking oil internally and adversely affect the valve timing adjustment. If found to deviating from targeted data the engine emergency mode will be activated. This will be indicated by a distinct change in engine running. The orange engine management warning lamp and a check message; On vehicles with N51/N52 engines this will appear at ignition recycle, on N55 engine it will display immediately. Remedial Action : Replace bolted connection of the VANOS adjustment unit.
23-12-2014: leftlanenews.com reported that BMW in the USA has confirmed plans to issue a nationwide recall for older 3-Series vehicles outfitted with Takata airbags. The expansion is said to include approximately 140,000 units from the 2004-2006 model years, adding to the 11,000 vehicles listed in the initial campaign focused on high-humidity states and territories. The National Highway Traffic Safety Administration had called on major automakers to orchestrate nationwide recalls for allegedly defective driver-side airbag inflators, however the agency is still allowing the passenger-side components to be fixed on a regional basis. "All five affected automakers have agreed to conduct a national recall of defective driver's side air bags made by Takata at our request," NHTSA acting administrator David Friedman said in a statement published by The Detroit News. BMW suggests none of the failures that prompted the NHTSA request have involved its vehicles, but the company nonetheless agreed to widen the recall.
9-4-2015: BMW has initiated a 'quality enhancement recall' on 2.0 litre N47 diesel engines. They are currently working their way through cars manufactured in 2007 and 2008, but owners need to contact their dealer themselves to request the work. Reader's 123d currently in for the work which at minimum involves replacing the timing chain, guide and tensioners. Recall seems to apply irrespective of mileafge. One readers car taken back at 130k miles.