11 Most Common Mercedes Benz SLK Problems (Explained)

The SLK is a sporty yet comfortable 2-door roadster that was first introduced in 1998.

Its most notable feature is its power retractable hardtop roof which was quite revolutionary for its time.

In this article, we’ll dive deep into the SLK’s common problems and their solutions.

1. Roof Issues

The SLK’s power-retractable hardtop has had persistent problems all throughout its three generations.

Similar to other convertibles, it will still leak if the seals are worn out despite it being a hardtop.

The powered top’s hydraulic pump and cylinders will also eventually fail over time.

In addition, the microswitches can also stop working which prevents the roof from opening or closing properly.

These issues can affect all model years of the SLK from 1998 to 2016.

The solid roof of early third generation SLKS from 2012 to 2013 can also start delaminating which creates a gap between the roof and the windshield frame.

Here’s how a few owners described their experience on SLKWorld.com:

“Had the same issue with my 2012 SLK. When there was a heavy downpour while driving at highway speeds, water started dripping in on the drivers side. Went to the dealership, they did a pressure test and confirmed the roof seal was bad.” 

“I recently purchased a 2012 Mercedes SLk350 with just 100k miles on it. I purchased it with the roof inoperable. When looking for the issue, I found that the O-rings on the upper front lock hydraulic cylinders. I replaced the o-rings with some I had in a O-ring kit and filled the hydraulic pump up and it worked perfectly. After using the top for a couple weeks I noticed the right lock cylinder was leaking hydraulic fluid out of the front seal.”

“My 2013 SLKs front roof area is coming loose from the frame. When driving 60 mph plus there is a lot of wind noise.”

Most roof leaks can be fixed by replacing the seals and weather stripping which should only cost a few hundred dollars at most.

Many SLK owners also use products like Gummi Pflege Stift to treat the rubber seals and prevent them from drying up and getting brittle.

In many cases, the rubber treatment can also get rid of the water leaks and squeaking noises that the roof makes when it opens and closes.

Poor alignment of the body and roof panels can also create gaps which allows water to leak through. To get this fixed, you’ll have to take the car to a body shop.

If the roof refuses to close or open properly, you can try spraying the microswitches with electronics contact cleaner to remove any built up corrosion.

The O-rings of the hydraulic cylinders can also be repaired by replacing the O-rings which should only cost a few dollars.

A new hydraulic pump from Mercedes Benz costs around $1,000 while cylinders go for about $500 each. 

There are also aftermarket kits that come with the pump and cylinders which cost around $1,000 in total.

You can manually open and close the roof with the help of an allen wrench to unlatch bolts and relieve pressure from the hydraulic pump.

You should be able to find tutorials and videos online showing the exact procedure for each generation of the SLK. 

If the solid roof in the third generation SLK starts delaminating, dealers will recommend replacing the entire roof for around $5,000.

Some third gen SLK owners were able to remedy their delamination issues by gluing the roof back onto the roof bar that’s under the headliner.

2. Starting Problems

Many first generation R170 SLKs eventually have issues starting up due to a faulty relay.

When the K40 relay fails, the starter won’t even crank even if the battery is fully charged.

This issue is more common in the early model years from 1998 to 1999. 

The facelifted models from 2000 onwards have less issues with the K40 relay.

When the K40 relay module fails, it can also cause engine stalling and rough running issues because it also controls the fuel pump.

Here’s how one user described their experience on BenzWorld.org:

“My SLK320 does not crank when I turn the key, and there is also no power reaching the fuel pump. The battery is absolutely fine.”

Another owner on SLKWorld.com had this to say:

“My 1998 slk230 just started symptoms of k40 relay issues. The dash lights come on and when I press the throttle, the engine does not respond although it is still running. Then, the dash lights go out and everything is back to normal. Just had the Benz dealer diagnose and they said it is a bad k40 relay.”

A new K40 relay module costs a little over $100 and is very simple to install.

You just need to take out the old module from the fuse box in the engine bay and swap in the new one.

Of course, you’ll still want to eliminate other possible causes of the problem such as:

• Faulty battery
• Key fob problems
• Starter issues
• Fuel pump issues

Some owners were also able to fix their faulty K40 modules by resoldering or reflowing the solder joints on the module’s circuit board. 

In some cases, some electronic components like relays and resistors also have to be replaced.  

3. Transmission Issues

The 7-speed transmission of the second generation R171 SLK can start acting up even before it reaches 100,000 miles.

The transmission can become problematic in all model years of the second gen SLK, starting from 2005 to 2011.

Symptoms of a faulty transmission include:

• Hesitation
• Slipping
• Stuck in gear
• Doesn’t shift properly

In a lot of cases, it’s the transmission’s valve body conductor plate or circuit board that’s causing these problems. 

Here is how users on SLKWorld.com described the problem:

“Just went through transmission issue and did a lot of research on what/why this happens in our SLKs. My car is 2007 with 102K miles. I got it about 6 months ago and it was several months before I had the first malfunction. After comparing other descriptions of transmission failures it appeared to me the most likely cause was a problem originating from the Conductor Plate.”

“If 722.9 transmission decides it no longer wants to shift gears while driving, you may be experiencing the speed sensor problem located on the conductor plate inside your transmission. Seems to bee fairly common. I just had the Conductor problem as well. P0717 and P0718 codes were present as well.”

“So my slk55 is suffering from the infamous turbine speed sensor issue with the conductor plate. The transmission has locked up 3-4 times over the last year, so I’ve known it’s been looming. Over the past 4 days, it’s done it a half dozen times, so looks like the time is near.”

The valve body conductor plate can be replaced and reprogrammed at the dealer but it can still cost over $1,000.

Some owners have also had their faulty conductor plates fixed by circuit board repair specialists to avoid any programming issues with the car’s software. 

Dealers may recommend replacing the valve body or even the entire transmission when it’s just the conductor plate that needs to be fixed.

The turbine speed sensors can also fail which results in the transmission to get stuck in gear until the vehicle is restarted.

4. Balance Shaft Issues

The V6 engines in the second generation SLK have a history of suffering from balance shaft failures.

The balance shaft is part of the timing system but its main purpose is to reduce engine vibrations.

Over time, the balance shaft sprocket wears out and throws off the engine’s timing.

This is a common problem on the early model years of the SLK280 and SLK350 from 2005 to 2007.

Other Mercedes Benz models that used the same M272 V6 engine also had similar issues.

Common symptoms of a looming balance shaft issue include:

• Engine rattle
• Check engine light
• Misfires
• Rough running
• Engine stalling
• P1200, P1208 or P1210 trouble codes 

Here’s how a few owners described their experience on SLKWorld.com:

“Took my 2004 slk 350 for servicing a couple of weeks ago and asked the garage to check out an intermittent check engine light that had began to appear not too long after purchasing this car in June this year. Next day the garage called to brighten up my day with their good news – definite balance shaft failure along with fault codes P1200 & P1208.” 

“Got some bad news from the local dealer after taking my SLK350 MY2006 in to deal with Check Engine light issue. The written version is: Balance shaft sprocket worn confirmed CEL is on; Connected DAS and performed a quick test. Found fault codes 1208 constant adjustment of the right bank intake camshaft retarded; 1200 constant adjustment of the right bank exhaust camshaft retarded; Timing cover will need to be removed to verify sprocket is worn.”

Due to the number of complaints and reported failures of the balance shaft sprocket in the M272 engine, Mercedes-Benz settled a class action lawsuit in 2015.

Replacing a worn balance shaft sprocket is an engine out repair which will cost several thousand dollars just for the labor.

If the balance shaft sprocket catastrophically fails, it can also severely damage the engine — requiring a full rebuild or a complete engine replacement.

If you’re worried about future balance shaft failures, you can check the engine’s timing and use a borescope to inspect the balance shaft sprocket for excessive wear.

5. Tail Light Issues

The first generation SLK’s brake lights are prone to failure due to excessive heat deforming the electrical contacts and tail light assembly.

This is a common fault in all model years of the R170 SLK from 1998 to 2004.

In a lot of cases, the tail light housing and electrical socket have melted or deformed enough that it’s difficult to fit a replacement bulb — let alone get it to light up.

Mercedes Benz issued a recall for the tail lights in 2005, but many owners eventually had the same problems after a few years.

Here’s how a few owners on SLKWorld.com described their experience:

“I have an R170 2002. The brake light, left side, is not working. I already replaced the light but it is still not working.” 

“My repair was also carried out in 2006, but I had trouble with it again in 2011. Dealer wouldn’t do anything about it, so I did what others are suggesting and just cleaned up and bent out the contacts a little bit – been good since.”

To fix the defective light, dealers will simply replace the entire tail light assembly which costs around $200 a piece.

Instead of replacing the assembly, many owners simply clean the electrical contacts in the bulb socket and bending them back into place.

In cases where the bulb socket is too damaged, you can splice in a new connector which should only cost a few dollars.

Many owners also replace the stock tail light assembly with aftermarket LED units to avoid having to deal with similar problems in the future.

6. PSE (Pneumatic System Equipment) Pump Issues

Problems related to the pneumatic pump, which controls the central locking system, are common in the first generation SLK.

Aside from the doors not locking or unlocking, other common symptoms of a faulty PSE pump include:

• Dome lights not working
• Trunk lamp won’t function
• Alarm goes off on its own

This is a common issue in all model years of the first generation SLK from 1998 to 2004 since the pump is located in the truck where it can easily get wet.

Here’s how a few owners on SLKWorld.org described their experience:

“I have problem with my 2003 SLK23. When I press the Key Fob, it flashes the lights but does not unlock the doors. It seems there is no problem with battery of key fob and the key fob sync to the car but does not trigger the pse pump.

“Have a 2003 slk 230 and experiencing these same problems. When I press the remote to unlock or lock the doors I hear the PSE working and going through its routine and then it stops I assume as it should. None of the door locks go up or down.” 

“I’ve had a trouble free couple of years with my 2001 Slk320. However water got in to my PSE pump in the boot and I had to source a replacement. Having found one and fitted it I find that the alarm goes off constantly and have removed the fuse for now. I gather that the new unit needs to be coded to the car.” 

If the PSE pump is faulty, you can replace it with a new one for around $300 to $500. Used units will also work and will be slightly cheaper.

Aside from finding the right part number, you also have to get the new pump coded to your vehicle.

Some owners have also taken out the working pump motor and placed it in their old units so they don’t have to go through the trouble of coding a new unit. 

After replacing the pump, you should also take care of any water leaks in the trunk to prevent it from getting damaged in the future.

There are also many cases where the door locks stop working due to leaks in the vacuum lines or other wiring/electrical issues. 

7. Peeling Interior Paint 

The paint used for the interior panels in the first generation SLK eventually gets scratched and starts peeling off.

The interior can start showing signs of damage in less than 10 years and only gets worse as time goes by.

Although this doesn’t affect the car’s drivability and functionality it is a very unattractive look on a luxury convertible.

Interior paint issues are common on all model years of the first gen SLK from 1998 to 2004. 

Some owners described their experience on SLKWorld.com  

“I’ve just purchased a 1999 SLK-230 and the only peeling interior paint is just behind the e-brake where the driver’s elbow rests.” 

“Just picked up a 1999 SLK230 Sport – Black with the two-tone Black/Oyster interior. Have had it a week. The interior peel was pretty bad so I have removed most of the dash and am stripping the paint. Found a latex paint remover that was safe for plastic and it is working very well.”

Another owner on BenzWorld.org had this to say:

“SLK230 1999 – same problem with painted interior. Over time I have thumb rubbed off quite a bit on the console while sitting at red lights in the heat and decided that the solid black of the plain plastic looks acceptable and would never need attention so now I want to remove the rubbery paint.” 

A lot of owners simply strip off the top layer of vinyl paint completely and leave the panels black which makes the interior much more presentable.

Those who want to preserve the original interior color can take off all the interior pieces, strip off the paint, then have it sanded and painted professionally.

If only a few pieces are scratched up, you can just touch it up using a bit of vinyl paint or just buy a replacement for the ruined piece.

8. Leaking Rear Main Seal

Oil leaking from the rear main seal is a common issue in the second gen SLK 55 AMG’s M113 V8 engine.

This is also common in a lot of other vehicles, but the SLK 55 can start developing a leak in just a few years.

It usually starts as a very small leak that goes unnoticed unless you take a closer look at the rear of the engine.

The valve cover gaskets are another common source of oil leaks.

Here’s how one owner described the issue on SLKWorld.com:

“I have had my 55 main rear seal replaced twice in 14 years. There is a pan/cover over that area, so unless you put it on the lift and remove that pan/cover, you will not see any drip until it overflows that pan.”

Although the rear main seal is very cheap, getting a new one installed is very labor intensive since the transmission has to be removed to access the rear of the engine and can easily cost over $1,000.

Many owners leave the leaking rear main seal alone until they have other major work that needs to be done to save on labor costs.

The only real consequence of a leaking rear main seal is some slight oil loss, so it’s a good idea to periodically check your oil levels.

9. Rust Issues

The first and second generation SLK can suffer from excessive rust problems if they’ve spent a lot of time in rust-prone areas.

Rust issues are particularly common among SLK owners based in the UK.

Some of the first generation SLK’s body panels aren’t fully galvanized so areas like the fenders are usually the first to show signs of corrosion.

The second generation SLK has a fully galvanized body, so it’s more resilient against corrosion. However, one of its weak points is the rear subframe which tend to rot out completely.

Here’s how a few owners on SLKWorld.com described their experience: 

“The bodywork of my silver 2000 SLK 230 is in pretty good shape, but unfortunately there’s rust under the 4 wheel arches. It’s creeping round the corner onto the front face in places.”

“Just had the rear subframe replaced on my SLK 200 following a scary moment on Monday when a suspension arm let go exiting a roundabout.” 

A new rear subframe can be had for a few hundred dollars and most experienced mechanics will have no trouble replacing the old ones.

Repairing rusted out body panels is more expensive because of the paintwork that’s involved.

If you want to keep your SLK rust-free and in pristine condition, you should regularly wash it if you take it through salt-treated roads.

Applying undercoating like Krown or Fluid Film in preparation for winter will also keep the car in good condition for longer.

10. Paint Issues

Third generation SLKs that were painted Mars Red, also known as Fire Opal Red, often showed lots of paint defects within just a few years.

Cars painted with this shade of red would have issues such as:

• Paint bubbling
• Peeling 
• Lots of small pin pricks or blisters
• Fading

Other Mercedes Benz models with the same color from the same era also suffered from similar problems.

Here’s how a few owners described their issues: 

“I traded my 2005 SLK for a 2012 350 with less than 17K miles. Car is great, zero mechanical issues, looks new….. except that about 3 months ago I got a discoloration on the paint on the trunk area and some small bubbles.”

“Just noticed a rash of tiny bubbles on the SLK. At first I thought there’d been a rainshower and a few drops of rain remained, but they don’t sweep away. Close inspection shows them to be in the paint – or at least in the lacquer layer. They’re squeezable, though they don’t go away.”

“My SLK 172 has had a full back to bare metal respray in Dec 2015 and now its back in again having another Back to metal respray. Thats 2 in 2 years.”

Similar to the rust problems, most of the complaints about paint defects usually came from the UK. Some dealers will respray the car for free even if it’s out of warranty.

The only way to fix the paint defects is to completely respray the entire car which can cost a few thousand dollars.

If only a few body panels are affected, you can have just those parts repainted but it will still be relatively expensive due to all the sanding and prep work that’s involved. 

11. Faulty Heated Seats

Broken heated seats is a very common problem in the second generation SLK.

The problem is often caused by faulty heating elements underneath the seats. 

Over time, the wiring for the heating elements wear out and just break apart. 

Even just putting extra weight on the seat or kneeling on the seat base can break the physical wiring of the heating elements.

It also usually just the heating elements in the seat base that stops working, while the ones in the seat back are less problematic.

This issue affects all model years of the second gen SLK from 2005 to 2011.

Here’s how a few owners described their issues on SLKWorld.com: 

“if the car has sat for a day without use and while driving it you turn on the heated seat the panel button has all 3 lights showing for about a minute or maybe a little less then it turns off. Of course the seat hasn’t warmed up at all but if you push the button again it will only stay on a couple of seconds and turn off again. This will continue for as long as you keep pushing it.” 

“Wife’s r171 drivers seat was heating till last month when only seat back was working now nothing.” 

A new seat base costs around $1,000 which is quite expensive just to get the heated seats working again.

Some owners were able to fix the broken heating elements by soldering the wires back together. 

However, this can be quite difficult since the wires are buried underneath the foam.

A few SLK owners were also able to replicate the functionality of the center heating element by simply fitting in an aftermarket heating pad.

Related: 19 Best & Worst Mercedes-Benz SLK Years (Facts & Stats)

Mercedes Benz SLK Pros & Cons

Pros

• Sophisticated styling
• Refined interior 
• Comfortable ride quality 
• Retractable hard top
• Lots of creature comforts
• Range of engine options
• Decently sized trunk
• Good reliability

Cons

• Base models aren’t very powerful
• Noise at highway speeds
• Potential roof leaks and problems

What Do The Reviews Say?

“While the SL-Class sets the standard in Mercedes’ lineup for convertibles, the SLK-Class isn’t far behind. They have the same general proportions (with a similarly blunt nose and large grille), nifty folding hardtop roofs and high-class interiors.”

“The SLK also delivers a similar driving character, which skews toward the more comfortable, cruising end of the drop-top persuasion. Because of its smaller proportions, however, it’s more agile and nimble. Its abilities are still short of what the iconic Porsche Boxster delivers, but going around turns in an SLK will easily put a smile on the faces of most drivers.”

“The 2016 SLK-Class is reasonably athletic when going around turns, and most drivers will find it quite enjoyable. It also provides the smooth, composed ride that Mercedes drivers expect.” 

“The SLK interior bears a strong family resemblance to the layouts of both the SL and the now defunct, but fondly remembered, SLS AMG.”

“The main interior drawback for the SLK is that it’s quite snug, even by compact roadster standards. The Z4, for example, gives larger drivers more room. On the bright side, the trunk is surprisingly accommodating for a two-door car whether the roof is up (10.1 cubic feet) or down (a still useful 6.4 cubic feet).”

2016 Mercedes-Benz SLK-Class | Edmunds

What’s the Resale Value of a Mercedes Benz SLK?

Here’s a quick look at used car pricing for the SLK on Edmunds at the time of writing.