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6 Most Common Mercedes BlueTEC Problems

What kind of problems does a Mercedes with BlueTEC usually have? In this blog, we’ve outlined the most important things you should watch for when you’re in the market for a Mercedes with BlueTEC. However, let’s first start with a quick answer:

Most commonly, Mercedes cars with BlueTEC have problems with a clogged diesel particulate filter. Furthermore, the DEF-heater can fail, and so can the exhaust pressure sensor. Finally, BlueTEC can have issues with the timing chain, glow plugs, and oil cooler leaks.

However, that doesn’t tell the whole story. In the rest of the article, we’ll discuss every single problem in detail. Furthermore, we’ll let you know how to identify it, fix it and how much it costs to fix. Read on!

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Also read: The Complete Cost Of Maintaining A Mercedes-Benz

1. Clogged Diesel Particulate Filter

Almost all diesel engines used in the Mercedes vehicles are equipped with Mercedes’s very own BlueTEC system. Out of many other problems, a common issue with the BlueTEC is the clogged Diesel Particulate Filter (DPF). Popular Mercedes diesel models, including – ML350, E350, R350, GL350, Sprinter, and R320 CDI, are affected by this problem.

The Diesel Particulate Filter (DPF) in the Mercedes BlueTEC traps and holds the soot particles. When it reaches a point where the soot needs to be emptied, it uses the regeneration process. Following this automated procedure, the ECU increases the temperature of the exhaust gases to over 630oC.

However, when the engine is not operating correctly, the automatic regeneration in the BlueTEC won’t start. In that case, you may notice any of these symptoms –

  • Illuminated check engine light
  • Poor acceleration
  • Car goes into limp mode
  • No throttle response
  • Decreased fuel efficiency
  • Reduced speeds

Furthermore, when the BlueTEC in your Mercedes experiences this problem, the engine light comes on, accompanied by error codes related to excessively high DPF filter soot content.

These error codes affect numerous 2010 and newer Mercedes models, including E, S, ML, GL, R, and G BlueTEC versions. In the case of sprinter vans, the throttle response would get very poor, limiting the vehicle’s speed to just 40 miles per hour or so.

To check your Mercedes for the problem with the DPF, you can use a generic OBD2 scanner to monitor the fault codes. However, if using a professional diagnostic scanner, the following error codes would be displayed –

  • P244B Diesel particulate filter (DPF) – Differential pressure too high
  • P2458 Diesel Particulate Filter Regeneration Duration
  • P2463 Diesel Particulate Filter Restriction – Soot Accumulation
  • 11A700 Diesel particulate filter – The soot content of the DPF is very high for regeneration. 
  • 11AF00 Diesel particulate filter – The soot content of the DPF is very high for regeneration. 

Suppose you find any of these errors in your BlueTEC or come across any common symptoms for this problem. Then don’t rush to replace the DPF filter, as cleaning the DPF filter yourself can solve practically all the earlier mentioned problems. In the video below, you can see how to clean a DPF filter on a Mercedes

It might also be possible that the issue is not with the DPF but with the temperature sensor, EGR valve, or swirl flap. Moreover, simple things like using the wrong engine oil can block the DPF, causing excessive soot buildup. So, make sure you use only approved engine oil.

However, if the problem is with the DPF, then to unblock it, the regeneration process has to be initiated manually. This can be done by following the instructions displayed in the scanner or cleaning the filter, as stated in the video above.

If you’re not a DIY person, fixing this problem can cost approximately $500 in the United States. In the worst-case scenario, if your DPF needs replacement, a new DPF filter for your BlueTEC can cost around $6000-$7000.

2. Problem With The DEF Heater 

Diesel Exhaust Fluid or DPF tank is another weak point of the Mercedes BlueTEC engine.

All the BlueTEC vehicles of Mercedes use Diesel Exhaust Fluid, also called AdBlue. Since this fluid is stored in an external tank, it can freeze in cold weather conditions. To prevent this from happening, the DEF tank is equipped with an electrical heater that can burn out.

If this happens, you will find a ‘check engine light. Although when the outside temperature is moderate and not very low, this problem won’t affect the engine performance. But during cold weather conditions, it can cause the DEF to freeze. Thus, hampering the performance of the engine.

To fix this problem, you would have to replace the DEF heater with a new one. The total replacement cost of the DEF heater can range from $2500-$3000 in the United States. But if you’d like to do this yourself, you can buy a DEF heater online and replace it for just under $1000.

3. Problem With The DPF Exhaust Pressure Sensor

Mercedes uses a DPF (Diesel Particulate Filter) exhaust pressure sensor like many other diesel cars. The primary function of this sensor is to govern the amount of exhaust flow restricted by the DPF.

Just like various other sensors, this one can fail too. In case of failure, it can give incorrect data misleading the actual DPF state.

Any of the following symptoms can be noticed if the DPF exhaust pressure sensor malfunctions –

  • Illuminated’ Check Engine’ light
  • Poor acceleration/Limp mode
  • Reduced engine power
  • Error code P1402 

In addition to the ‘check engine light. The most prominent indication of this problem is that your car would struggle to accelerate. This is mainly because you are driving without the turbo’s assistance, with the boost turned off. Also, the ECU would restrict the maximum RPMs.

However, the good thing is you can still change the gears, but the car would have sluggish acceleration, which can be fatal. This condition is not the same as in the limp mode, where the vehicle gets stuck in second gear.

To fix this problem, replacing the DPF sensor is the only solution. The DPF sensor can be found underneath your Mercedes in the vicinity of the particle filter, above the transfer case. Replacing the DPF sensor is easy, and it is not expensive.

4. Oil Leaking From The Oil Cooler 

Oil leakage is a common problem with many Mercedes BlueTEC diesel cars. However, this issue is most prominent in the 3.0-liter V6 diesel engines, designated engine code – OM642. 

These OM642 engines can develop leaks from the oil cooler seals that can degrade prematurely by the high heat it is exposed to. The oil cooler is placed at the center of the engine’s ‘V’ at the rear end of the engine compartment.

Essentially, all engines generate heat while running, but the OM642 engines can produce a lot of heat. Add to that the position of the oil cooler, which exposes it to the heat the engine produces. Thus, causing severe damage to the oil cooler seals. The video below shows where the oil cooler is located and what seals start leaking.

Further, to add to the complications. The leaking oil from those oil cooler seals tends to flow backward, only visible from underneath the vehicle. This leakage would only be detected during routine service or oil changes.

Also, it is widespread that the technician would incorrectly identify the leak’s origin as a rear main seal. Adding up to unnecessary costs and repairs would not solve the problem. On the other hand, an experienced Mercedes technician would accurately identify the true culprit or check the oil cooler for any leaks, saving you both time and money.

To fix this problem, the technician would replace the seals with the new upgraded ones from Mercedes. Also, since changing the seals requires removing the turbocharger, intake manifold, and many other components, the replacement process includes high labor costs.

5. Problem With Glow Plugs

The glow plug is vital in every diesel engine, including the Mercedes BlueTEC. The primary purpose of a glow plug is to cold start the engine. In essence, it is a powerful electric heater. 

In older cars that have high mileage, the problem of glow plug failure is expected. Symptoms of this problem include –

  • Rough idling for the first few minutes
  • Long engine cranking time

Though replacing the glow plug is a relatively simple job, the glow plug can be stuck and break in the process when not done carefully. So, use a plug removal tool to remove the glow plug safely.

There is a possibility that the glow plug module can be faulty instead of the glow plug in rare cases. In that case, the glow plug module should be replaced, which costs around $150 in the United States. 

6. Problem With The Timing Chain

A timing chain is an essential component of any engine. Without it, your Mercedes won’t work. Like other components, the timing chain is also subject to wear and tear. The timing chain in the Mercedes BlueTEC engine stretches much faster than it should. Although later, Mercedes redesigned the chain and sprockets. But, older BlueTEC models and some new ones can still have this problem.

A loose timing chain can cause wrong timing of the crankshaft, and the camshaft would lag. This would also lead to a low fuel economy and reduced engine performance.

The excessive soot suspended in the oil causes the timing chain and the sprockets to wear quickly. The original sprockets and timing chain can last much longer with high-quality oil, 5000-mile changes, and better oil filtration.

You can lessen the chances of complete timing chain failure by regularly maintaining your Mercedes. Also, manufacturers don’t place an upper limit on the longevity of the timing chain, and they believe it will last the engine’s lifetime. Thus, failure of the timing chain can depend on many factors like – mileage, driving conditions, servicing, etc. 

If a Mercedes has higher mileage, the timing chain can wear much faster, leading to severe engine problems. Though replacing the timing chain in the Mercedes BlueTEC is rare, sufficient care should be taken to avoid such instances.

To timely identify any problem with the timing chain, you can look for these common symptoms –

Rattling Sound

Timing chain noises are the most obvious indication of this problem. Unusual vibrations and engine sounds are warning signs that indicate a loose timing chain. A smooth, consistent sound means the timing chain is excellent. However, if you hear a rattling sound, then it may mean the timing chain is slacked.

Slack permits the chain to hit the timing cover, producing metal debris. This overtime can also form a hole in the cover, causing the oil to leak. So, if you hear any abnormal rattling sound from your BlueTEC engine, the timing chain is loose. The video below quickly shows you what this sounds like.

Engine Misfiring

The chain might skip a gear on the camshaft or crankshaft because the timing chain in every engine, including the Mercedes BlueTEC, can loosen over time. 

As a result, the engine’s timing becomes uncalibrated, resulting in misfires. In some cases, the engine may also lose accelerating power. Moreover, if the timing chain breaks due to excess slack, the metal pieces can cause severe damage to the engine.

Engine Won’t Start

A broken timing chain can cause the engine to fail because the engine won’t have the proper compression to start. If the timing chain in your BlueTEC breaks while driving, the piston will stick in contact with the valves. The valves can also bend and damage the engine.

If you suspect any of these symptoms in your BlueTEC, you have a loose timing chain. It is recommended that you should have your chain inspected on time. Mercedes offers a certified method to measure the amount of chain slack for the OM651 and the OM642. It typically costs around $500-$600. Lastly, the entire cost of replacing the timing chain with a new one would be about $3,500 – $5000, taking in mind the high labor cost involved

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