The Mercedes Benz GL450 is a full-size three-row SUV that was first introduced in 2006 and renamed as the GLS in 2016.
It’s basically the SUV version of the S-Class that features a powerful V8, luxurious interiors with lots of creature comforts, and outstanding ride quality.
In this article, we’ll dive deep into the GL450’s most common problems and how you can deal with them.
Table of Contents
1. Air Suspension
GL450s are equipped with an air suspension system that can fail after a few years and can be very expensive to repair.
Some of the things that can leak or break include:
- Air shocks
- Air lines
- Electronic sensors/modules
Here’s how one owner described their issues on BenzWorld.org:
“The wife’s 2007 GL450 just started getting message to visit workshop with suspension icon. I’ve had both front struts replaced but not the rear. After a couple days the rear right is bottomed out.”
Another GL450 owner on MBWorld.org had this to say;
“I have a 2010 gl450. I recently spend 2k on the 2 front air struts and left rear air bag. 2 years ago I spend like 2500 on the air compressor and installation plus the valve block filter included. One air bag popped when putting on tires so that was another 500 dollars. In total I have spent 5k on this benz and it has 100k miles.”
Any vehicle that has air suspension can be expensive to maintain, so it’s not unique to the GL450.
Replacing the air shocks will be significantly cheaper if you go with aftermarket parts from brands like Arnott.
Some owners who plan on keeping their GL450 for a long time swap the air suspension have converted theirs to a coil spring setup.
2. Oil in Wiring Harness
The cam position sensor in the second generation GL 450 has a tendency to leak oil and damage the ECU.
Once the cam position sensor starts leaking oil, it drips onto the wiring harness and can reach the ECU.
When the oil contaminates the ECU’s electronics, the truck eventually will have random electrical glitches and trouble codes.
This problem is especially common in the 2013 model year of the second gen GL 450, which was its first year of release,
A few GL450 owners shared their experience on MBWorld.org:
“I just purchased a 2013 GL450 with 60,000 miles. I was aware this could be an issue and purchased the car anyway, without enough research on the front end to check for it at the dealer. I just pulled my cam sensors and all 4 have oil on the connector on the harness side. I do not see any oil in the connectors on the front magnets. I pulled the ECU connector and do see oil inside the plastic ECU housing, and some oil on many of the pins. This only on the “front” section of the ECU. The back is clean.”
“My GL450 is at the shop with the same exact issue. They quoted me “around $4K” for a temporary repair, which means it could happen again, or 15K for a complete engine overhaul. The $4K temp repair was to replace the engine module and degrease the wiring harness, but it won’t stop the oil from leaking out and causing the computer to short out again.”
“I recently brought my 2013 GL450 into the MB dealership because of a check engine light. They did an oil change and service when they went to clear the check engine light they said it kept “throwing 20 codes”. After a few days of investigation they called and said there was oil leaking onto the wiring harness and therefore they needed to replace the wiring harness for $7,500 total about $3,500 for parts and $4k for labor.”
Aside from replacing the camshaft position sensors, it’s also important to clean out any existing oil and sludge on all the components up to the ECU.
Dealers will likely want to replace a lot of the contaminated parts instead of cleaning them, so the repair can end up costing several thousand dollars.
If the ECU has already been damaged, it will have to be replaced and likely cost a pretty penny. You can of course look for a used one to save some money.
You can periodically check if you need to replace the sensors by unplugging them and checking for oil on the connectors. Once you see oil, you’ll have to replace them soon.
Some owners also install aftermarket wiring harness extensions that can easily be replaced once the oil starts leaking. This reduces the chances of oil getting on the OEM harness.
3. Transmission Valve Body
The 7-speed transmission in the first generation GL 450 can start acting up even before it reaches 100,000 miles.
The transmission can become problematic in all model years of the first gen X164 GL 450, ranging from 2007 to 2012.
Symptoms of a faulty transmission include:
- 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 MBWorld.org described the problem:
“I just purchased a used 2007 GL450 with 68K miles. After 2 months, I noticed it shifting funny. I would pull out from a stop sign and it would rev up (rpms go way up) and not move very fast. It only does this every so often. I pulled the codes off and I’m getting P2767,P2768. It looks like valve body or conductor plate needs to be replaced based on what I’ve read from other people. This is ridiculous for transmission problems with only 69k miles on it.”
“It happens to ALL X164 GL’s. You are stuck with the repair bill. Should be around $1,200 at the stealership. Mine went out around 100k miles but that may have been because I had the fluid and filter changed around 35k miles.”
“I have a 2007 GL450 and very sporadically the transmission will stop shifting and I won’t have very much power. The RPMs will go up but the car won’t go any faster.”
Another owner on BenzWorld.org had this to say:
“GL450 with 75,000 miles. Valve body in transmission failed. $2,200 so far. Still at dealership.”
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 might 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. Vibration During Braking
A number of second generation GL 450 owners have complained about a noticeable vibration or shuddering whenever they apply the brakes.
This issue seems to be extremely common in the early model years of the second gen X166 GL 450.
Here’s what a few owners on MBWorld.org had to say:
“My GL 450 2013 has only 7k miles.. and it looks like it has a problem with the brake. On the local is hard to feel it, but when i speed up on the freeway and push the brake pedal my car vibrates in an unsafe manner.”
“This is a common issue, search this forum on rotors. There was a bad bunch of contamination. Also, when finding those threads they will tell you to make sure your dealer replaces both the rotors and the pads, or a re-occurrence is likely.”
A manufacturing defect in the brake rotor is the most likely cause of the fairly common braking issue that owners experienced.
Older GL450’s will likely have had their original brake rotors and pads replaced several times by now, so it shouldn’t be of much concern today.
If you still experience vibration during braking, you can try aftermarket brake pads and rotors or check for worn wheel bearings.
5. Door Handle Locking Issues
Faulty door handles is a very common problem that affects all model years of the first generation Mercedes Benz GL450.
The touch-sensitive exterior door handles eventually stop responding after a few years of use and being exposed to the elements.
It’s also usually the rear driver’s side door that goes out first because it’s the most used one.
This issue is prevalent in the 2007 to 2012 model years.
One owner on MBWorld.org described their issues below:
“I have an issue on my 09 GL450 with left rear door handle, it stopped reacting to the touch to unlock the car, other doors are working fine. but before that happened, I noticed that the button on that same handle would not lock the car every time I push on it or I have to push it a few times, but now it’s completely dead.”
Another owner on BenzWorld.org had similar problems:
“I let a family member borrow my GL450 for around 6 months and now notice that upon getting it back, only the driver’s side rear door will allow me to lock from the black button on the handle. The driver’s door, and both on the passenger side don’t have functionality… The door locks themselves work just fine when using the remote lock/unlock buttons.“
New door handles are around $100 a piece so they’re not too expensive to replace. But you may go through a few door handles if you’re going to keep the vehicle for a long time.
If it’s freezing outside, you may just need to give the door handles some time to thaw out a bit and they’ll start working properly again.
The door lock actuators can also fail at some point.
On MBWorld.org, one owner had to replace a door lock actuator when they experienced the following:
“The front driver door will not lock/unlock electronically, meaning key fob, exterior handle touch (Keyless Go), interior buttons, or the autolock while driving will not actuate the driver door bullet plunger. All of the other door plungers will actuate (lock/unlock) as expected with any of the aforementioned methods, just not happening with the driver door. Pulling on the interior handle will raise the bullet plunger up and unlock successfully so the manual mechanism part works.”
Replacing the actuators can be expensive because you’ll need to get an assembly that costs around $500.
Otherwise, it’s a fairly straightforward repair that can even be done at home.
Some were able to repair the actuator by cleaning the motors and replacing a spring.
6. Cylinder Bore Scoring
The M278 twin-turbo V8 engine in the second generation GL 450 has been known to suffer from scoring or excessive scratching of the cylinder bore surface.
This problem can occur in the older model years from 2013 to 2014, or before the V8 was replaced by a turbo V6 in the GLS450.
Cylinder scoring is more common if the truck has spent a lot of time in colder climates. The lower temperature makes it harder for the engine and the oil to warm up, so lubrication is less than ideal on startup.
Although it’s common for the X166 GL450’s engine to develop scratches on the cylinder lining, minor cases don’t usually lead to any drivability or reliability problems.
There are also more cases of cylinder scoring on the higher-powered GL550, which uses the same engine, compared to the GL450.
In worst case scenarios, the scoring or pitting of the cylinder lining is bad enough that the piston can move around.
This results in symptoms such as:
- Engine knock or rattle
- Loss of compression
- Excessive oil consumption
- Smoky exhaust
Over time, the cylinder scoring could lead to the engine seizing up.
Here’s what users on MBWorld.org had to say:
“On a couple of X166 GLs I recently fixed for others (one with camshaft replacement due to misaligned tone ring and the other needed some fuel injectors), both showed cylinder scoring/scuffing but after camshaft/injector replacements both drove fine. So, I believe there are lot more M278 GL’s out there with scuffed cylinders that drive fine.”
“I have a 2014 Mercedes-Benz GL450 4Matic V-8 x166 with 175,000 miles. Just had dealership fix a valve cover oil leak and complete tune-up, but now I have an engine light, knocking and power loss from cylinder 2. Dealer scoped and there is some scoring. All dealer could offer was $37k engine replacement.”
If the cylinder bore is badly damaged, you’ll need a new engine or have the cylinders re-sleeved at a machine shop and put the engine back together, both costing several thousand dollars.
If you want to know how bad the cylinder scoring is, you can ask a mechanic to inspect it with a borescope.
7. Timing Chain Issues
The second generation GL 450 and GL 550 have a tendency to develop timing chain issues even before it reaches 100,000 miles.
Both use the M278 twin-turbo V8 but the GL 550 produces more power.
The most common symptom owners have reported is an engine rattle that lasts for a few seconds after a cold start.
The rattle eventually goes away once oil pressure has built up.
This is also a common problem on other Mercedes Benz models equipped with the M278 engine.
In some rare cases, the rattle could also indicate a stretched or loose timing chain which can eventually cause major engine damage.
Here’s how a few owners described their issues on MBWorld.org:
“My GL550 is making a small rattling sound at cold startup that lasts about 2 to 5 seconds, then I don’t hear it anymore. When having other repairs performed at the local dealership, they said this is common to GLs with the M278 engine, and that the Technical Bulletin LI05.10-P-056435 states replacing the timing chain tensioners on each bank of cylinders will remedy the issue.”
“I had this done on my 2013 GL450, but it was under warranty, so don’t know the cost. Given that it’s a well-known issue and that there is a TSB on it”
Another owner described their experience on BenzWorld.org:
“I have a 2015 GL-450 that’s making a knocking noise on a hot engine startup after it’s been sitting 20 mins. Had the timing chain and tensioners replaced now the dealer is saying it’s the camshaft tensioners but that’s another $5500 to replace.”
Mercedes-Benz released a TSB for early builds of the M278 that recommends replacing the timing chain tensioners and installing new check valves to get rid of the rattle.
If it’s just the tensioners that are problematic, it shouldn’t cause any long-term reliability or drivability problems aside from the rattle on startup.
Getting this repair done at the dealer can cost around $1,500. The parts aren’t very expensive and you may get a better price if you have it done at an independent Mercedes Benz specialist.
8. Transfer Case Issues
Both the first and second generation GL450 can suffer from transfer case problems as they age.
When the transfer case’s internal components start wearing out, owner have reported the following symptoms:
- Clunking or popping noises
- Grinding noises
- Noises when turning at full lock
- Lurching when accelerating
In a lot of cases, these symptoms are caused by a stretched out transfer case chain which can be easily replaced.
The same transfer case problems are also fairly common in the GL550, as well as in other Mercedes Benz models equipped with 4Matic from the same period.
Here’s how a few owners described their issues on MBWorld.org:
“Our 2013 GL450 with off-road package has developed the transfer case chain issue with grinding noise at acceleration and turning.”
“I bought a GL450 CPO at 55k miles. It is now at 90k and I noticed a grinding noise. I took to MB service and they are telling me that it is the transfer case that needs to be replaced and will cost me $6k to replace.”
Many owners were able to fix their transfer case problems by replacing the transfer case chain which costs around $100 to $150.
Dealers will often recommend replacing the entire transfer case which can easily cost over $5,000, so it’s best to have an independent specialist or transmission shop do the transfer case chain replacement.
Some owners were even able to replace the chain in their garage at home in an afternoon. It’s not a very difficult job if you follow tutorials and videos that can be found online.
If the transfer case has too much damage and has to be completely replaced, you can also get a remanufactured unit for around $3,000 to $4,000.
8. Timing Cover Oil Leak
Oil leaking out of the timing cover, also known as the front engine cover, is a common issue in a lot of second generation GL450s.
This issue also affects the GL550 which uses the same engine as there were problems with the original sealant used during assembly.
The oil leak is usually pretty minor and won’t affect the oil levels dramatically, but it will cover parts of the engine in used oil.
Here’s one owner’s experience on MBWorld.org:
“2013 w/80K miles. GL450. I took the car in for a steering wheel recall work, and was told that there is an oil leak from the engine front cylinder head covers. This needs to be resealed.”
Another user had this to say in response:
“Common defect from the factory. Resealing is not strictly a “must” but the leaks make a mess and there will be loss of oil over time. Suggest you get them fixed. Dealer is a ripoff. Indy can do this job.”
Fixing the oil leak isn’t too big of a job, but the timing covers have to be taken off and the old sealant has to be taken off.
After applying new sealant, you’ll also have to replace the aluminum screws that bolt down the timing cover.
An independent Mercedes Benz specialist should be able to take care of it quite easily and for a much cheaper price compared to a dealer.
After applying the new sealant, it shouldn’t leak as quickly and can last the entire lifetime of the vehicle as long as the repair is done properly.
Most owners only get the leak fixed when they need other work done on the engine to save on labor costs.
9. Coolant Leaks
Coolant leaks are a common problem in the first and second generation GL 450 as the hoses, seals and plastic coolant lines become brittle over time.
All model years of the Mercedes-Benz GL from 2007 to 2014 will suffer from coolant leaks as they age.
Common symptoms of coolant leaks include:
- Smell of coolant
- Visible leaks and drips
- Low coolant warning on the dash
- Heater doesn’t work
Some of the more common sources of coolant leaks in the GL include:
- Water pump
- Turbo coolant lines
- Radiator hoses
Cracks in the radiator and leaks from the turbo coolant line are very common problems in the second generation GL450.
Here’s how a few owners on MBWorld.org described their experience:
“My GL450 has had the check coolant message come on a few months ago . I took to service and they said it just needed topping off. but today it came in again and I see that from the hose that goes from reservoir to radiator is white and shows coolant on the lower larger hose and on upper housing.”
“I have had a slow coolant drip form my GL450. After a trip to the local exotic car repair shop they said it was the radiator so I purchased that and changed it myself, but it still leaked (although possibly in a different spot) so I then changed the lower hose (where it looked like it was coming from) but now it’s still leaking from somewhere.”
“Turbo coolant lines get really brittle really fast on these engines. I’m on my third set at 80K.”
A new radiator for a Mercedes GL only costs around $300 if you look online.
New coolant hoses and lines are also not very expensive, but the repair costs can still reach several hundred dollars if you replace them all and refresh the entire cooling system.
Some coolant lines can be very difficult to get to which increases the total repair costs because of all the labor that’s involved.
Many owners replace the cooling system components as part of the truck’s preventative maintenance whenever they have to go in for major repairs to save on labor costs in the future.
Lots of DIY enthusiasts have also replaced the radiator, water pump, and coolant lines on their own with a little bit of help from the Internet.
10. Worn Suspension Components
Aside from air suspension problems, the GL450 can also suffer from suspension component failures due to the truck’s size and weight.
The control arm bushings are a common weak point and dealers can only replace the entire control arm which can easily cost over $1,000 for both sides.
The sway bar end links also wear out eventually and cause squeaking and clunking sounds in the front, but this is a fairly cheap and simple repair.
Here’s how a few owners described their experience on BenzWorld.org:
“I took my 2008 GL450 in for an alignment and mechanic said that one of the left upper control arms bushings had failed. Recommended replacing both upper control arms at a cost of $1340 including alignment.”
“My 2007 GL 450 has a creaking noise in rear drivers side above the wheel. My shop diagnosed this as rear control arm, ball joint and lower shock bushing.They cant identify which one so they are recommending replacing all.”
Another owner on MBWorld.org had this to say:
“On my 2007 GL450 the front suspension clunking noise was corrected by replacing the left and right sway bar end links (link rods).”
If you only hear some slight squeaking from the suspension, you can try lubricating the bushings and other rubber suspension components with some silicone spray or even some WD-40.
Instead of replacing the entire control arm, you can get a set of aftermarket bushings for significantly less and most experienced mechanics should be able to easily them swap out.
Aftermarket sway bar links also cost less than $50 and should be a straightforward repair.
If the noises and clunking still don’t go away, it could be struts that need to be replaced.
11. Idler Gear Sprocket Problems
Early builds of the GL450 used an idler gear sprocket that had lots of reported failures.
The idler gear sprocket is part of the timing chain system which keeps the engine’s internal rotating components in sync.
When the idler gear’s teeth wear out or break off, the engine’s timing will be off which can eventually cause severe engine damage.
This issue is prevalent on the 2007 to 2008 model years of the first generation GL450.
Common symptoms of a worn idler gear include:
- Engine rattle
- Rough running
- Check engine light
- Rough idle
Here’s how a few owners on MBWorld.org described their experience:
“My 2007 GL450 is starting to show signs of the dreaded idler gear issue. I checked the vin and it does fall into the affected cars range. I’m currently at 80k miles and got the codes p0017. Also cold start is pretty rough and got a pretty bad misfire the other day which just fixed itself somehow. I hear the chain under hard acceleration although the car still runs fine. My mechanic quoted me 3600 to pull the engine and change the idler gear and timing chain.”
“Early M273s did have the idler sprocket issue (no actual balance shafts on V8s unlike the M272 V6). If you plug the VIN into lastvin.com it will give you the serial number for the engine and as long as the last 9 digits are greater than .30088611 you’re supposed to be ok. My GL has 249K miles, and based on the noises it is making and error codes it is throwing, something or somethings related to the timing chain are wearing out.”
“My first GL was an early 2007 model (6/06 production) that was on the idler problem list. I got the dreaded CEL with corresponding codes, but already had over 100k miles on it. Just kept driving it with no issues other than the CEL until I sold it at 238,000 miles. Not sure how many miles are on.it now, but I know it’s still on the road – 3 years later.”
Due to the number of complaints and reported failures of the idler gear sprocket in the M278 V8, Mercedes-Benz settled a class action lawsuit in 2015.
Replacing a worn idler gear is an engine out repair which will cost several thousand dollars in labor alone.
If the idler gear catastrophically fails, it can also severely damage the engine — requiring a full rebuild or a complete engine replacement.
However, many owners of older GL450s have reported that they’ve been running the car with a check engine light on and timing related trouble codes for years without any issues.
12. Water Leaks
Water leaking into the cabin of the first generation GL450 can damage many electronic modules inside and cause all sorts of strange electrical gremlins.
The front and rear SAM (Signal Acquisition Module) can easily get damaged when the cabin floor gets flooded.
In many cases, even excess moisture or dampness can eventually end up corroding many electrical components under the floor.
Aside from fixing the water leaks, replacing all the affected electronics can easily cost several thousand dollars.
Here’s what a few users on MBWorld.org had to say:
“I bought a 08 450 GL 6 months ago and had no serious issues until one mont ago the computer systems went haywire. Took it to MB dealer and they found the areas under the driver’s seat full of water. It appeared the water had been there for some time based on rust on th surface at the top of water line. Dealer says it’s $11,000 to replace modules, wiring harness, other components damaged by water.”
Since our purchase in 2016, we have loved our GL450, a 2008 model. It had about 90K, no reported incidents, and a single owner prior…The BIG engine light came on, the windows started going up and down, and a big tire-out sign blazed. The wipers started going off and stopping randomly. Then the handbrake sign came on… So the battery well is clogged, yes. But water logging is rampant in other places too. The front SAM is bust because of the water and needs replacement. Apparently, the Merc GL450 has a false bottom, and the carpets do not sit on a metal surface, unlike regular cars. Rather, atop other electronics that Mercedes crammed in that space. The carpet was soggy but no leaks in the sunroofs
“It’s either coming in around the tail lights or around the seals on the panoramic third row sunroof.”
“Water intrusion around the rear d-pillar and cabin air filter box will fry sensitive electronics – don’t buy one that is wet inside.”
If you’re in the process of picking up a used GL450, avoid examples that have signs of water damage or water stains on the headliner or carpets.
Strange electrical gremlins can also be caused by a weak 12-volt battery, so make sure you have a fresh battery that’s fully charged up before troubleshooting anything.
You can also try cleaning out all the corrosion on the circuit boards of different affected components instead of replacing them.
Electrical gremlins in modern luxury cars like the GL450 can be difficult to fix, so it’s best to have an independent Mercedes Benz specialist or an automotive electrician assess the situation before you start throwing parts at it.
The V8 seems prone to cylinder scuffing, bad valve guides and chain tensioning problems, all fatal or very expensive issues.
13. Secondary Air Injection Pump Failure
Issues with the secondary air pump in the first generation GL450 is a common problem that many owners have had to deal with.
The secondary air injection pump is part of the truck’s emissions controls and helps the catalytic converters to function more efficiently on startup.
When the secondary air pump fails, owners have reported the following symptoms:
- Check engine light
- P0410 trouble code
- Loud electric motor noise at startup
This is a common problem in all model years of the first gen GL450 from 2007 to 2012.
Here’s how a few owners on MBWorld.org described their experience:
“My 2012 GL450’s secondary air pump is broken again. Last time it was repaired by a garage but this time I want to DIY.”
“I have a 2012 GL450. In April 2019, I had the secondary air pump replaced by a garage because it was broken. It has been 10 months and it failed again. The dedicated 40 amp fuse for it is blown. I checked the resistance of the air pump, it is like 0.1 ohm. When I disconnect it from the electric plug and directly applied 12V to it, the air pump won’t run. So it is bad again.”
In many cases, a secondary air pump failure is actually caused by a faulty relay. This only costs a few dollars to fix and you just have to replace the old one that’s plugged into the fuse box.
Some dealers might charge around $700 to $1,000 for a new pump, but an aftermarket one from a reputable brand like Bosch only costs around $200 to $300.
It’s also possible to open up the air pump and clean out its internals using an electrical contact cleaner to get it running properly again.
Shops that specialize in rebuilding starters or alternators can also refurbish the old air pump, but it might cost just as much as a new aftermarket part.
Mercedes Benz GL450 Pros & Cons
- Excellent ride quality
- Luxurious and quiet interior
- Lots of tech and creature comforts
- Powerful V8 engine
- Good towing capacity
- Third-row seats
- All-wheel drive
- Expensive parts and maintenance
- Floaty handling
- Poor resale
What Do The Reviews Say?
“The GL450 gets a gas-powered 4.7-liter turbocharged V8 that produces 362 hp and 406 lb-ft of torque. Acceleration to 60 takes just 6.2 seconds, which is impressively quick for a luxury SUV with a “base” level engine. Its fuel economy is estimated at 16 mpg combined (14 mpg city/19 mpg highway).”
“The 2014 Mercedes-Benz GL-Class comes standard with antilock brakes, stability control and traction control, active front head restraints, front and rear side airbags, full-length side curtain airbags, a driver knee airbag and a driver attention/drowsiness monitor.”
“Mercedes likes to call the GL-Class a three-row S-Class, and based on its highway manners alone, we’re inclined to agree. The GL tracks straight and true, shrugging off pavement imperfections and generally feeling invincible. Credit here is partly due to the standard Airmatic suspension system, which automatically lowers the vehicle at higher speeds for improved road holding.”
“Materials quality is excellent in the GL’s cabin, with supple, tight-fitting panels everywhere you look. The many technology features start with Mercedes’ excellent COMAND system, which consists of a central color screen, dashboard buttons, steering wheel controls and a multifunction knob on the center console. It can seem a little intimidating at first, but COMAND is one of the best interfaces on the market, enabling both simple and more complex tasks to be executed with ease.”
What’s the Resale Value of a Mercedes Benz GL450?
Here’s a quick look at used car pricing for the GL450 on Edmunds at the time of writing.