The BMW N53 engine was produced from 2006-2013. Being the final naturally aspirated inline-6 that BMW will likely ever produce, it is the last of a tradition from BMW that dates back to 1968. As a result of BMW’s constant improvements to their straight-6 formula, the N53 is a fantastic and well-rounded engine, completely with many of BMW’s most modern engine technology including direct injection and double-VANOS.
However, that doesn’t exclude the N53 from having a number of common issues, primarily consisting of high pressure fuel pump failure, injector failure, NOx sensor/catalytic converter wear and tear, spark plug failure, and coil pack failure. In this guide, we’ll cover those 5 BMW N53 common problems in detail.
BMW N53 Background
For all intents and purposes, the N53 engine can be thought of as an extension of the N52 inline-6 that was produced from 2004 to 2015. The two engines are almost identical in terms of their overall construction, barring a few changes. The primary difference is that the N53 was designed to be a high-efficiency version, leading to changes in the design of the N53’s fuel and exhaust systems. BMW was able to reduce fuel consumption in the N53 engine by adding direct injection and a nitrogen oxide storage catalytic converter. This catalytic converter required low sulfur content fuel to run properly.
Fitted in BMW E9x 3-Series, E60 5-Series, and even the F10 5-Series until 2011. The N53 replaced the N52 in most markets, except for the North American Market and Australia. These markets were excluded due to high sulfur content in the fuel. While most markets got the updated BMW N53, the U.S., Canada, and Australia continued to get the N52.
5 Common Problems with the N53 Engine
Like its N52 predecessor, the N53 truly represented BMW at their best as far as the inline-6 engine layout is concerned. Over 45 years of developing inline-6 engines led BMW to truly nail down how to build an inline-6 that was not only powerful but also extremely reliable. That all culminated in the N53.
Ultimately, the N53 is an extremely reliable engine that only suffers from a handful of notable engine problems. While the engine has had issues with direct injection fuel pump failure (similar to most early BMW direct injection engines), injector failure (see previous parenthetical), NOX issues, spark plug failure, and coil pack failure, there are very few true N53 engine problems to note. Here are the N53 engine problems that we’ll be covering here:
- Fuel Pump
- NOX Sensor/Cat Issues
- Spark Plugs
- Coil Packs
If you would rather consume this content via a video, check out our BMW N53 Common Problems video below:
1) N53 High Pressure Fuel Pump (HPFP)
This is the first common and most prevalent issue to come up with the N53. High Pressure fuel pumps were such an issue when the engine first came out that BMW issued a recall on the engine. The N53 uses the same HPFP as the BMW N54, and these issues are well documented. The high pressure fuel pump is a very important element of any direct-injected engine’s operation, as it is responsible for pressurizing the fuel before it reaches the injectors and is sprayed into the combustion chamber.
There are a few reasons why high pressure fuel pump is such a big headache on the N53. For one, a failing high pressure fuel pump can lead to all kinds of drivability issues. Additionally, BMW high pressure fuel pumps are notoriously expensive and difficult to replace. With it being such a common issue, there are tons of forum posts about N53 HPFP failure occurring randomly and without any consistency as to when the failures occur. Some N53 owners experience a failure as early as 15,000-20,000 miles while others make it north of 100,000 miles without issue.
If you are interested in reading about high pressure fuel pump failure in more detail, take a look at our BMW N54 High Pressure Fuel Pump Failure article.
Symptoms of N53 HPFP Failure
- Long crank
- 1/2 engine light
- Rough idle
- Stuttering acceleration
When the high pressure fuel pump is failing it will not deliver enough fuel to the engine for proper operation. The lack of fuel flow is what causes long cranks, rough idling, and stuttering while accelerating. The 1/2 engine light may illuminate and the car will likely continue to drive until the HPFP completely fails and does not flow adequate fuel for the engine to fire.
Mileage for Failure
High pressure fuel pumps on the BMW N53 may fail at any mileage; many likely failed early on and were replaced under the recalls and extended warranty. In 2012/2013, after multiple attempts, BMW finally re-designed the HPFP which seems to have resolved the issues. If you are looking into purchasing a model with the N53, be sure to check the maintenance records to ensure the HPFP has been replaced either by recall or by the previous owner. Most N53 HPFP’s likely experienced failure early on and received the updated fuel pump, but there may be a few out there still running the original faulty part.
2) N53 Fuel Injector Failure
The N53 went from port injection to direct injection with Piezo injectors (similar to the BMW N54). With this change, came a learning curve and lots of changes and reprogramming to these parts. Though the BMW N53 and N54 both used direct injection featuring Piezo injectors, the actual part number and injectors are different on each engine. Despite this difference, they suffered a similar fate with common failures.
Symptoms of N53 Fuel Injector Failure:
- Limp Mode
- Rough Idle
- Poor Fuel Economy
- Check Engine Light
Unlike the HPFP issue that does not flow enough fuel, the injectors typically fail by developing leaks and dumping extra fuel into the cylinders. This extra fuel causes misfires, rough idle, poor fuel economy and potentially check engine lights and limp mode.
If you do need to replace the injectors, do not buy them refurbished or used, and try to get them to match the same index. The newer fuel injectors that fixed the early issues have different indexes; it is important to note that different index fuel injectors can not be mixed on the same bank (i.e. cylinders 1-3 or 4-6). After replacement, they will need to be coded. Not replacing them properly can cause the engine to still run rough, which may lead into the next two issues. These 3 of the 4 common N53 problems have to do with misfires and rough idles.
3) Bad BMW N53 NOx Sensor/Cat
NOx sensor, NOx cat issues are some of the most frequently reported issues on the N53 engine, especially as the engines age and exhaust components begin to fail. Since the N53 was designed to be a low-emissions engine, it is equipped with both a NOx sensor between the last CAT and rear back box and a NOx catalytic converter.
A NOx sensor has a pretty straightforward job; it measures the amount of nitrous oxide that is emitted by the engine at two points in the exhaust system. A NOx catalytic converter is used to collect the excess NOx produced by the N53. The N53 produces more NOx than a typical engine due to the fact that it is a stratified charge engine, allowing for it to run a higher compression ratio, increasing efficiency but also raising NOx production.
Over time, the NOx sensor can begin to malfunction, and the NOx catalytic converter fails to capture an adequate number of NOx ions, leading to performance issues and other engine problems. High sulfur content in fuel leads to faster degradation of NOx cats, which is why the N53 was only offered in parts of the world where fuel has very low sulfur content.
Symptoms of Bad N53 NOx Sensor/Cat
When either the NOx sensor or NOx cat begins to malfunction, there are a number of noticeable symptoms that generally accompany that. In the majority of cases, neither of these issues are truly serious and you’ll be able to drive your car regardless. However, a failed NOx cat can cause you to fail MOT or emissions testing if not repaired first.
- Rough Idle
- Metalic rattling sound on startup
- Smoke coming from the exhaust until engine is warm
- “Aging NOx Catalytic Converter” engine code
- Inconsistent engine performance
Bad N53 NOx Sensor/Cat Diagnosis/Fix
Due to the fact that many of the symptoms of a bad NOx sensor/NOx cat fall in line with a number of other common N53 failures, including bad injectors and a bad HPFP, it is important to make sure that the sensor/cat is truly the issue and not something else. NOx cats are notoriously expensive to replace, so it is a good idea to do a thorough diagnosis before purchasing a new one.
Luckily, diagnosing a failing N53 NOx sensor/NOx cat is relatively easy with a diagnostic tool. BMW INPA is the most commonly used diagnostic tool to check for NOx issues, as it will tell you which engine mode your N53 is running at any time. If you can see that your engine is entering the stratified engine mode, you likely don’t have an issue with either component. If the engine fails to run consistently in stratified mode, there is an issue with either the sensor or the cat. If the diagnostic tool is presenting an “Aging NOx Catalytic Converter” code, it means that the cat is to blame for your issues.
Ultimately, there are a few solutions if your NOx catalytic converter is going bad. You can replace the aging unit with a fresh one, which can be extremely expensive but will guarantee that you won’t have any issues smog testing. There are also a number of NOx cat delete options on the market via software tuning. A company called Bimmerproffs offers a NOXEM emulation tune for about £320 which tricks the DME into thinking that the cat is in working order. You can also install an aftermarket high flow cat and have Bimmerfroffs tune your DME to accommodate that. You can check out their website here.
4) N53 Spark Plug Failure
Not a huge issue on the BMW N53, but something I saw come up several times with owners attempting to correct their misfire and rough idle situation. Obviously, spark plugs are a common maintenance item regardless, but N53 plugs have been known to wear prematurely, causing misfires and rough idles. Leaking fuel injectors dump extra fuel near the spark plug tips causing premature wear. Also, if you have had a valve cover gasket leak, there is a chance that oil has soaked the plugs.
Symptoms of Bad N53 Spark Plugs
- Rough idle
- Stuttering acceleration
- Loss of power & torque
- Reduced engine responsiveness
In addition to premature wear, spark plugs naturally wear down over time and become less effective or faulty, causing the same symptoms above. They should be replaced roughly every 40,000-50,000 miles, and are a cheap repair that can easily be completed by novice DIY’ers. If you know your spark plugs have not been replaced in that time frame it may be a good idea to knock out the repair as preventative maintenance.
5) N53 Bad Ignition Coils
Another BMW N53 issue causing power loss, misfires, and rough idles (same or similar symptoms as spark plugs). The coil packs are usually an overlooked issue. It seems most owners report this as the last item they replace after the injectors, and spark plugs to fix the misfires and rough idles. While it is difficult to diagnose with certainty, getting to the coils is relatively easy; they actually sit on top of the spark plugs and must be pulled out to replace the spark plugs. If the engine has over 50,000 miles (or if they have not been replaced in the last 50,000 miles), chances are the ignition coils may be faulty or under-performing.
Compared to other engines in the BMW lineup, I would say this engine is reliable and ready for a long life. While some of the 5 listed common problems with the N53 can be expensive to replace, none of them are so serious that they truly compromise the reliability of the engine completely. Of course, older engines with high mileage may develop oil leaks or other issues as a part of standard wear and tear, though they are not overly common issues. A fuel pump may put you in limp mode, but will not retire the car to the junkyard. The same goes with for the injectors, spark plugs, and coil packs.
Reliability score 1-4 with 4 being the worst: 1
BMW produced a fantastic engine to make its mark as their last naturally aspirated inline-6 engine. Let me know what you think of the engine if you own one or your experience with it.
If you liked this post, check out our article on the N63.