Most Common Mercedes ML320 and ML320 CDI Problems

What kind of problems does a Mercedes ML320 or ML320 CDI usually have? In this post, we’ve outlined the most important things you should watch for when you’re in the market for an ML320. However, let’s first start with a quick answer:

The Mercedes ML320 has air conditioning problems caused by a faulty blower, compressor issues, low freon levels, or a malfunctioning electric motor. Furthermore, the door locks may stop working, the check ESP/ABS lights can turn on, the power steering fluid can leak, or the EGR can cause the car to diminish its range.

The Mercedes ML320 CDI has similar issues but can additionally suffer from diesel particulate filter issues, causing reduced engine performance and fuel efficiency, particularly during short trips. Furthermore, faulty glow plugs may lead to difficult cold starts and rough running. Lastly, fuel injection system problems may result in additional engine performance issues.

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!

1. The Blower Is Not Working

This is a fairly common occurrence in the ML320, which might have a particular underlying cause depending on the diagnosis. If the blower is not working, it’s probably the fuse “44”, located behind the coolant bottle, or the motor itself is causing the problem.

Take the cover off and see the 44 fuse. Check the voltage to see if it is in working condition; if not, change the fuse, and you are good to go.

Suppose you don’t see the instruction page, no worries. The fuse will have a number 30 on top of it, which means it’s 30 amp. It is small in size and is located at the top right corner. The cost may vary from $100-$300.

Compressor Issue

Another reason why the air conditioning might not work would be the compressor. If the  ML320 compressor motor is not spinning and there is no problem with the blower or the amount of freon, it’s most definitely the compressor. A compressor can cost around 800 dollars figure including labor.

Low Freon Levels

Low freon levels can also affect the air conditioning. Freon cans are readily available in the market with gauges that set the level right. If the level is upset, the cooling will not take place. If everything else seems okay, the most likely issue is the cold/hot dials on the dashboard, and you are only getting hot air. The kit is available for about $100.

Only Getting Hot Air

The hot/cold dial for controlling the air conditioning temperature is connected to an electric motor, known as the blend motor. Most of the time, this motor is the culprit. It acts as a distributor that channels the cold and hot air according to the dial. If you don’t hear an electric sound of this motor activating while turning this dial, while everything else seems fine, then it’s the motor issue.

This motor is located behind the glove box and has a control arm that can be moved manually if you want to; it will save some bucks.

• Take out the glove box
• Turn off the fan
• put the dial on cold
• Pop up the metal lever
• push the control arm inwards for cold
• For having the hot feature, turn the dial to hot and pull the control arm outwards.

Replacing the motor is a hassle, and it’s not an easy DIY fix. It takes a lot of time and requires removing the upper dashboard itself.

2. Door Locks Are Not Working

If you have problems with the door lock/actuator and would not listen to your commands and behave erratically, it’s time to change the actuator.

You will hear strange squeaking noises, and locks will not initiate or act sluggish. These actuators cost around $200 and can be replaced by removing the door panel, drilling the rivets, and opening the screws that hold the panel and the side airbag.

After carefully removing the airbag, the door actuator wiring will be exposed, and just above the door hinge inside the cabin, there is a small hole with a hex bolt that can be unscrewed with a 4mm Allen Wrench. Make sure you have a long wrench length that is longer than the width of the door.

After loosening the hex bolt, put the key in, and turn it to the right. While holding the key to the right and having the wrench firm in place, pull the key out slowly with a gentle wiggle, and you will have the lock out in the open. To remove the door handle, unscrew the remaining screws above and below the hinge.

There will be a rubber seal on the side of the hinge, carefully take that out, use the 4mm Allen wrench to loosen the bolt inside, and pull the door handles towards the back and out perpendicular to the door. 

And now, to reach the actuator, two rivets on the top and two on the bottom need to be drilled and pried out to get to the actuator. Once the rivets are drilled, they must be put in place with a rivet gun after replacing the actuator. Once the railing comes off, remove the switch, and the actuator will come out.

3. The Check Light Problem

It’s a heavy vehicle that drives like a truck, so if the steering feels heavy or the acceleration feels weak, it’s probably not an issue; it’s just how it drives typically. Mechanically this truck is sturdy, and the engine is pretty reliable.

We can find these cars with more than 300k miles with their original engine, with the head still intact, but the motors and sensors are quite troublesome. These “lights” are a huge problem for the ML320 owners.

The ETS ABS Light Has Turned On

These pesky lights can be a nightmare for the ml320 owners. These often turn on, causing many headaches, and the dealers would ask for thousands of dollars to fix, even though the problem might not even be that expensive.

The first thing is to run a scanner check and reset if the problem persists, then move on to the next possible cause. These lights are connected to the ABS motor one way or another. So after the scanner check, the second thing is to check the ABS motor. These motors can cost around $100 in the aftermarket, while the dealers might ask for thousands of hard-earned dollars.

To get to the left ABS motor, you can take out the windshield washer and the electrical connectors, making the job much more manageable. You can try to fix the motor itself if you want to, not that it’s recommended. You should only do this if you have a lot of mechanical knowledge. It will be much cheaper, maybe around $5 to fix.

These ABS motors are prone to failure because of the worn-out brushes, L5-5H brushes to be concise, and the bearings, BR0018 would be the exact number. It’s also good to change the ABS modulator and the motor to ensure the problem is fixed, but it’s doubtful that this modulator is the problem. After changing the motor, the ETS ABS lights will go away.

You would require a swivel socket wrench to remove the screws holding this motor in place. When taking this motor out, be careful not to damage the bearing of the modulator that holds the motor. Use a screwdriver to keep that bearing in place, and then slowly and gently take the motor out of that holder. This ABS motor has a product number, A163 431 85 12. 

The BAS/ESP Light Has Turned On

Make sure that it has proper wheel alignment. When driving straight, put the steering at dead center and see if the car turns to the left or the right. If it turns, you can have the alignment fixed and turn the steering to the left and then to the right to reset, and this light will go away. If this is not the case, move to the next possible solution.

If the vehicle brakes automatically for no reason, it’s most likely the yaw sensor in the center console. You can easily replace that sensor, and the issue will be fixed. If the vehicle does not brake automatically for no reason, let’s move to the next possible issue. 

The lateral acceleration sensor would cause the BAS/ESP light. The exact part number for the lateral acceleration sensor is “A 163 542 06 18 Q02”, after replacing this sensor, turn the steering all the way to the left and then all the way to the right to reset everything, and these lights will go away.

To get to the lateral acceleration sensor, you can take out the center console and the vents if you want to have a clear working space, then you look up the sensors and replace the lateral acceleration sensor; with that, you are good to go.

4. The Low Range Problem

When you put the vehicle in low range, the light turns on and goes away. The light may also blink during the start-up, which is abnormal behavior. Sometimes, we wouldn’t even move as the transfer case will be stuck in the middle of the high range and low range.  It is caused by the motor attached to the transfer case. After replacing this motor, the problem will go away.

This is located underneath the vehicle and is held in place by 10mm bolts. And I digress; the American-made Mercedes is not hard to work on because it’s not overly engineered. Just two bolts hold on the rear bumper. Everything in this SUV is straightforward to access, and every other bolt is a 10mm hex bolt.

So, after replacing this motor, your low range and high range will work perfectly. Apply the silicone around the edges to ensure that it’s appropriately sealed—this motor costs around $100.

P0400 Code

EGR is the culprit here, the things to check:

• EGR Valve
• Solenoid, It usually clicks when given an electrical supply
• The vacuum lines
• Power feed

Now, this code is common in the ML320. It is commonly caused by the clogged EGR pipe having debris in it. We can take the EGR valve out and clean it with the EGR pipe, and this code will disappear. This is not an easy DIY job, so you might have to pay a professional to clean this for you and check for other possible issues.

The EGR is located near the exhaust manifold and once the EGR valve is out, check whether it’s making a vacuum or not and see if it has some issue with the connectors.

5. Power Steering Fluid Leakage

This is a prevalent issue in the ML320 because the power steering reservoir has a small plastic connector that often breaks and causes leakage of the power steering fluid and a lot of noise. A similar problem can also occur in the SLK200 and W204 is also known for its power steering problems. The part number for the reservoir is “000 460 01 83” It is also advised to have an O ring ordered as well, “000 466 18 80”, because these often break while taking out the reservoir.

The cost of this reservoir and the O ring/gasket is about $30. And the genuine Mercedes Power steering oil costs $18, Krytox grease is recommended for the O ring, but you can also use alternatives. You can get the Krytox grease for about $20.  

While adding the steering fluid, turn the steering wheel from side to side to remove any air bubbles from the system. If the engine is cold and wasn’t running previously, you fill-up to the lower level mark, and if the engine was running, you could fill it up to the high mark.

6. ML320 Has Fuel, But The Gauge Shows Empty

This is a common problem because refueling the vehicle when the tank is more than halfway full. Mercedes advises not to fill the tank until it goes less than halfway full. If you have this gauge issue, you can reset the fuse containing the algorithm to store the refueling data.

To get to this fuse, open the side panel from the passenger feet side on the right. You will see two plastic screws that hold the panel in place. Turn them 90 degrees and pull them out. The fuse in question is a 15 amp located on the top left corner, between a 20 amp fuse and a 40 amp fuse. The numbers are displayed on top of each fuse, and you can check the back of the panel you removed, which has all the fuse information. You can look for the F5/15 amp fuse.

Once you find which one it is, take it out and put it back. You will have the fuel gauge in its rightful place where it belongs.

7. ML 320 Starts And Shuts Down After A Second

If the vehicle starts and shuts down in a second, the likely issue is the ignition switch sensor; this sensor is located at the key ignition place. You can take out the covering behind the steering to get to this sensor. This sensor is about $25.

8. Diesel Particulate Filter (DPF) Issues (ML320 CDI Only)

The Diesel Particulate Filter (DPF) plays a vital role in reducing emissions from diesel vehicles by capturing and storing exhaust soot. A common issue with the DPF is clogging or blockage, which can stem from frequent short trips where the engine does not reach the optimal temperature.

When the engine doesn’t get hot enough, it prevents the soot in the DPF from burning off, a process known as ‘regeneration‘. This lack of proper regeneration can lead to a buildup of soot, causing reduced engine performance and fuel efficiency.

To identify this issue, look out for symptoms like decreased fuel economy, increased oil consumption, the vehicle entering ‘limp mode’, or an illuminated check engine light. Often, an error code related to the DPF system will be stored in the vehicle’s onboard computer.

There are a few solutions to consider when dealing with a blocked DPF. One common method is to perform a forced regeneration using a professional-grade vehicle diagnostic tool. This procedure increases the exhaust temperature to burn off the excess soot. Alternatively, the DPF can be manually removed and professionally cleaned. In severe cases, replacement of the DPF may be the most practical solution.

You can learn more about cleaning to solve this problem here:

The cost of resolving DPF issues can vary widely based on the required solution. A forced regeneration procedure might cost around $100-$200 when performed by a professional. DPF cleaning services are more costly, usually around $300-$400. If a full replacement is necessary, the price can go into the $1000-$2000 range, including parts and labor.

9. Glow Plug Failure (Mercedes ML320 CDI Only)

Glow plugs play a vital role in diesel engines, pre-heating the cylinders to aid in cold-weather starting. They create a hot spot in each cylinder that ensures the diesel fuel ignites even when the engine is cold.

When glow plugs fail, it’s typically due to wear and tear or deposits building up over time, which can decrease their effectiveness. This deterioration can lead to hard starts, particularly in colder weather, and potentially cause the engine to run roughly until it’s warmed up. I’ve seen this happen in a wide range of vehicles including BMW’s X5 and other luxury diesel vehicles.

Identifying glow plug failure can be relatively straightforward. Symptoms to watch for include difficulty starting the engine when it’s cold, a cylinder misfire code in the vehicle’s computer, or the glow plug warning light illuminating on your dashboard. In more severe cases, failed glow plugs might cause a noticeable decrease in power and overall vehicle performance.

Addressing glow plug failure generally involves their replacement, a task that varies in difficulty depending on the vehicle model. While it’s possible to replace glow plugs yourself, the job can be challenging without the right tools or expertise, especially if the old glow plugs are seized and difficult to remove.

The cost associated with glow plug replacement can also vary. If you choose to do it yourself, the price of new glow plugs typically ranges from $10-$20 each, with most vehicles having one for each cylinder. If you decide to have a professional handle the job, the total cost, including labor, can range from $100 to $400, depending on the number of glow plugs needing replacement and the labor rate of your mechanic.

10. Fuel Injection Issues (Mercedes ML320 CDI Only)

Fuel injection problems are primarily associated with the common-rail diesel injection system used in this model. The fuel injection system plays a pivotal role in the proper functioning of the engine, injecting precise amounts of fuel into the cylinders at the right moment for optimal combustion.

Fuel injection issues can arise from various causes, including clogged fuel injectors, faulty fuel pumps, or issues with the fuel pressure regulator. Any of these issues can disrupt the correct functioning of the fuel injection system, leading to decreased engine performance, rough idling, and even engine misfiring.

Symptoms of fuel injection issues can be subtle at first, but they typically manifest as a noticeable decrease in engine performance and fuel efficiency. You might experience rough idling, an engine that’s hard to start, or even misfires during acceleration. In many cases, the check engine light will illuminate on your dashboard, and a fuel-related error code will be stored in the vehicle’s onboard computer.

Addressing fuel injection issues can involve several solutions depending on the specific problem. Cleaning the fuel injectors can often resolve minor clogs, and this task can be performed using a specific fuel additive or by a professional mechanic using a dedicated fuel injection cleaning machine. In more severe cases, faulty components like the injectors, fuel pump, or pressure regulator may need to be replaced.

The cost of resolving fuel injection issues can vary significantly based on the severity of the problem. Fuel injector cleaning services typically range from $50-$200, depending on the method used. Replacing one or more fuel injectors can cost anywhere from $300 to over $1000, depending on the cost of the parts and labor.

As with any vehicle, regular maintenance and prompt attention to any issues can help prevent more serious problems down the line, ensuring your ML320 CDI continues to deliver its renowned performance and reliability.

Closing Thoughts

Throughout this comprehensive guide, we’ve delved into the various issues you might encounter with the ML320 and the CDI variation. We’ve provided insights on how to identify these problems, possible solutions, and the potential costs associated with fixing them. Armed with this knowledge, you’ll be better equipped to handle and prevent these problems, ensuring the continued performance and reliability of your vehicle.

But remember, every vehicle has problems including every Mercedes. Whether we’re talking about the transfer case problems of the 4Matic, rust issues on the E320, or the loud engine on an ML350 every vehicle comes with problems. So keep that in mind when you review any list of common problems.

Other challenges could surface given the unique circumstances of each vehicle. So, stay vigilant and keep learning. Remember, understanding the problem is the first step in fixing it. Keep this guide handy, and you’ll be well-prepared for the road ahead!