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2010 MERCEDES-BENZ GLK350

Owner reports · Recalls · Investigations

More warning signs than most GLK350 years

Owner complaints for the 2010 MERCEDES-BENZ GLK350 are substantially higher than the model-year median of 114.

About this comparison →

When problems were reported

Mileage at the reported incident

72 reports with mileage · 169 unknown

NHTSA’s mileage field refers to the reported incident, not necessarily the filing date. This shows report counts, not the likelihood of a failure.

What to inspect

Issues worth paying extra attention to based on owner reports.

  • Air Bags. Review the 149 owner reports in this category and discuss these concerns during a pre-purchase inspection. Read reports →
  • Fuel/propulsion System. Review the 26 owner reports in this category and discuss these concerns during a pre-purchase inspection. Read reports →
  • Suspension. Review the 14 owner reports in this category and discuss these concerns during a pre-purchase inspection. Read reports →

NHTSA owner reports · September 18, 2026 snapshot.

12 crash reports2 fire reports6 injury reports

What owners actually said

241 reports
Mileage unknown · Apr 21, 2023
Tires

The tires were purchased from NTB in August 2022. I noticed a bubble on the side of the tire 3 April. We contact NTB in Columbia,MD because we purchased them from the location and they were also put on at the location. They stated, we can purchase a new tire but there was nothing they could do. We purchased the tire from Walmart…

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The tires were purchased from NTB in August 2022. I noticed a bubble on the side of the tire 3 April. We contact NTB in Columbia,MD because we purchased them from the location and they were also put on at the location. They stated, we can purchase a new tire but there was nothing they could do. We purchased the tire from Walmart.com and took it into the Walmart Tire and Lube. The technician Kevin replaced the olde tire with the new and asked why didn’t we get a free replacement tire from wherever it was purchased from since it was a new tire and defective. We asked him to show us a defect and he showed a small slit inside the tire which caused the tire bubble. He then brought it back to us and placed it in our trunk to give back to NTB. NTB declined to replace the tire stating it was a Pirelli issue and we needed to contact them.

NHTSA ODI #11518340

Mileage unknown · Feb 16, 2023
StructureSuspensionUnknown Or Other

Subframe of the car rusted and rotted from inside out. to the point of rear suspension completely detached from subframe. it caused my car to fish tail and lose control under even slow breaking conditions. once we discovered the problem we were told the car was a death trap and was absolutely unsafe to operate. we found out th…

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Subframe of the car rusted and rotted from inside out. to the point of rear suspension completely detached from subframe. it caused my car to fish tail and lose control under even slow breaking conditions. once we discovered the problem we were told the car was a death trap and was absolutely unsafe to operate. we found out this is a common problem for this MB model type. the problem was already under recall in Europe. there are thousands of existing owner complains about the exact same issue. MB USA initially refused to acknowledge the problem, but on 2/14/2023 they sent a memo to all US dealers to repair rotted subframe for free under "extended warrantee". however, they refused to pay for the full repair even after dealership specifically informed them that it was not possible to complete the repair without replacing thrust arm and rod, which were damaged due to the Subframe failure. this incident endangered me and my family, cost $2000+ out of pocket for repairs in addition to the loss of access to my vehicle for at least 3 weeks.

NHTSA ODI #11507640

Mileage unknown · Feb 7, 2023
Service BrakesSuspension

After breaking hard the vehicle started to pull left and the rear felt like it had locked up. I took it immediately to my local mechanic who diagnosed a prematurely rotted out subframe. I am in the process of having MB review and quote for the repair.

NHTSA ODI #11506087

Mileage unknown · Jan 3, 2023
Service BrakesStructure

I had my 2010 Mercedes GLK in for B service today (Jan. 3, 2023), and the repair team inspected the vehicle and informed me that I have a RUST HOLE approximately 1" x 2" in size located adjacent to an attachment point for the wheels in the REAR SUBFRAME. If it breaks, it could cause the vehicle to become difficult to control. …

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I had my 2010 Mercedes GLK in for B service today (Jan. 3, 2023), and the repair team inspected the vehicle and informed me that I have a RUST HOLE approximately 1" x 2" in size located adjacent to an attachment point for the wheels in the REAR SUBFRAME. If it breaks, it could cause the vehicle to become difficult to control. Additionally, they informed me that the BRAKE LINES are also RUSTING/WEAKENING. If the brakes fail while driving it could cause loss of control of the vehicle. Since these are hidden parts that I typically can't see, I had no warning that there was anything wrong until I had it in for routine maintenance. I have the invoice for the oil change, with a notation from the repair team regarding these parts. The vehicle is available for inspection should it be necessary.

NHTSA ODI #11499957

Mileage unknown · Jan 3, 2023
Fuel/propulsion System

Gas leak when filling tank with fuel. Last year I had fuel pump replacement Smells like gas in my garage and I noticed leak This is not good

NHTSA ODI #11499861

Mileage unknown · Dec 28, 2022
Structure

Premature rear subframe corrosion due to design of component, vehicle is available for inspection upon request. If control arm detaches geometry of suspension will change and divert into another lane and cause a crash, the issue was confirmed by an independent service center. The vehicle is due to be inspected by the manufacture…

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Premature rear subframe corrosion due to design of component, vehicle is available for inspection upon request. If control arm detaches geometry of suspension will change and divert into another lane and cause a crash, the issue was confirmed by an independent service center. The vehicle is due to be inspected by the manufacturer 12-30. No warning of issue as the majority is covered by body panel.

NHTSA ODI #11499110

Mileage unknown · Dec 7, 2022
Suspension

I am the owner of a 2010 Mercedes GLK 350 with 102,531 miles. The problem I have is the rear subframe rusted with a crack on the rear subframe making it very dangerous if the rear subframe fails while driving. This issue has become very popular with the c class Mercedes Benz.

NHTSA ODI #11496509

149,000 miles · Nov 28, 2022
Structure

The contact owns a 2010 Mercedes-Benz GLK350. The contact stated while driving 40 MPH and depressing the brake pedal, the rear end began to fishtail and shattered. The contact stated no warning light was illuminated. The contact was able to continue driving slowly to a nearby repair shop. The mechanic informed the contact that t…

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The contact owns a 2010 Mercedes-Benz GLK350. The contact stated while driving 40 MPH and depressing the brake pedal, the rear end began to fishtail and shattered. The contact stated no warning light was illuminated. The contact was able to continue driving slowly to a nearby repair shop. The mechanic informed the contact that the rear subframe was corroded and had detached from the vehicle. The contact was able to drive to her residence. The contact took the vehicle to the local dealer, where it was diagnosed with needing the rear subframe to be replaced. The vehicle was not repaired. The manufacturer had been informed of the failure. The failure mileage was approximately 149,000.

NHTSA ODI #11495179

Mileage unknown · Nov 25, 2022
Fuel/propulsion SystemUnknown Or Other

Mold in a/c

NHTSA ODI #11494866

Mileage unknown · Oct 16, 2022
Service BrakesSuspension

On 10/5/22, my wife was driving her 2010 GLK 350 to work, suddenly she felt the break pedal was going deep inside easily and noticed break fluid light warning sign in dashboard. She was scared to drive and slowly drove car to Mercedes authorized technician. After diagnosis, MB technician said the issue in not just on break fluid…

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On 10/5/22, my wife was driving her 2010 GLK 350 to work, suddenly she felt the break pedal was going deep inside easily and noticed break fluid light warning sign in dashboard. She was scared to drive and slowly drove car to Mercedes authorized technician. After diagnosis, MB technician said the issue in not just on break fluid leaks but the entire breaking system is failing due to rear subframe rust which holds the entire suspension and body. He said car is not safe to drive will cost $4K to $10k to repair. Called another dealer near by said the same as this is common issue with Mercedes due to snow the subframe rust during winter. It is ironic that even with frequent servicing with dealer they never found these rust issue early because rusting process started early on any metals. Went online to dig deeper on this issue and surprised this issue is widespread check https://mbworld.org/forums/c-class-w204/805501-rotted-rear-subframe-2.html#post8650716 Apparently Mercedes recalled all C class cars to replace subframe as they realized it is their design issue in Europe, UK and Canada. Here in USA dealers give excuses saying it due to winter snow it rust even though they did not catch such dangerous safety issue in the car. Imagine if how severe this break safety issue. Please take action on Mercedes Benz to address this safety issue US, specially it has been addressed in UK, EU, and Canada.

NHTSA ODI #11489463

Official recalls

5

19V010000 · Air Bags:frontal:passenger Side:inflator Module

Jan 9, 2019

Mercedes-Benz USA, LLC (MBUSA) is recalling certain 2014 C250, C300 4Matic, C350, C63 AMG, E350 4Matic Coupe, E350 Cabrio, E350 Coupe, SLS AMG Cabrio, SLS AMG Coupe, 2014-2015 C250 Coupe, C350 4Matic Coupe, C350 Coupe, C63 AMG Coupe, GLK 350, GLK250 BlueTec 4Matic, GLK350 RWD, 2015-2017 E400 4Matic Coupe, E400 Cabrio, E400 Coupe, 2014-2017 E550 Cabrio, and 2014-2016 E550 Coupe vehicles sold, or ever registered, in the states of AL, CA, FL, GA, HI, LA, MS, SC, TX, PR, AS, GU, the MP, and VI or "Zone A." Additionally, MBUSA is recalling certain 2012-2014 C250, E350 4Matic Coupe, SLS AMG Cabrio, 2012-2015 C250 Coupe, C350 4Matic Coupe, C350 Coupe, C63 AMG Coupe, 2011 C300, 2011-2014 C300 4Matic, C350, C63 AMG, E350 Cabrio, E350 Coupe, SLS AMG Coupe, 2015-2016 E400 4Matic Coupe, E400 Cabrio, E400 Coupe, 2011-2016 E550 Cabrio, E550 Coupe, 2011-2015 GLK350 4Matic, GLK350 RWD, and 2013-2015 GLK250 BlueTec 4Matic vehicles ever registered in the states of AZ, AR, DE, DC, IL, IN, KS, KY, MD, MO, NE, NV, NJ, NM, NC, OH, OK, PA, TN, VA, and WV or "Zone B." MBUSA is also recalling certain 2012-2014 C250, E350 4Matic Coupe, SLS AMG Cabrio 2012-2015 C250 Coupe, C350 4Matic Coupe, C350 Coupe, C63 AMG Coupe, 2010-2011 C300, 2010-2014 C300 4Matic, C350, C63 AMG, E350 Coupe, 2011-2014 E350 Cabrio, SLS AMG Coupe, 2015-2016 E400 4Matic Coupe, E400 Cabrio, E400 Coupe, 2016-2017 E550 Cabrio, 2010-2016 E550 Coupe, 2010-2015 GLK350 4Matic, GLK350 RWD, and 2013-2015 GLK250 BlueTec 4Matic vehicles ever registered in the states of AK, CO, CT, ID, IA, ME, MA, MI, MN, MO, NH, NY, ND, OR, RI, SD, UT, VT, WA, WI and WY or "Zone C." These vehicles are equipped with air bag inflators assembled as part of the passenger frontal air bag modules that may explode due to propellant degradation occurring after long-term exposure to high absolute humidity, temperature and temperature cycling.

Consequence & remedy

Consequence: An inflator explosion may result in sharp metal fragments striking the passenger or other occupants resulting in serious injury or death.

Remedy: MBUSA will notify owners, and dealers will replace the passenger frontal air bag module, free of charge. The recall began March 29, 2019. Owners may contact MBUSA customer service at 1-800-367-6372.

18V043000 · Air Bags:frontal:passenger Side:inflator Module

Jan 10, 2018

Mercedes-Benz USA, LLC (MBUSA) is recalling certain 2013 C250, C250 Coupe, C350 Coupe 4Matic, C300 4Matic, C350, C350 Coupe, C63 AMG, C63 Coupe, E350 Cabrio, E350 Coupe, E550 Cabrio, E350 Coupe 4Matic, E550 Coupe, GLK350 4Matic, GLK250 Bluetec 4Matic, GLK350, SLS Coupe, SLS AMG GT Coupe, and SLS Roadster vehicles sold, or ever registered, in the states of Alabama, California, Florida, Georgia, Hawaii, Louisiana, Mississippi, South Carolina, Texas, Puerto Rico, American Samoa, Guam, the Northern Mariana Islands (Saipan), and the U.S. Virgin Islands or "Zone A." Additionally, MBUSA is recalling certain 2010 C300, C300 4Matic, C63 AMG, E350 Coupe, E550 Coupe, GLK350, and GLK350 4Matic vehicles ever registered in the states of Arizona, Arkansas, Delaware, District of Columbia, Illinois, Indiana, Kansas, Kentucky, Maryland, Missouri, Nebraska, Nevada, New Jersey, New Mexico, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Virginia, and West Virginia or "Zone B." MBUSA is also recalling certain 2009 C300, C300 4Matic, C63 AMG, and C350 vehicles ever registered in the states of AK, CO, CT, ID, IA, ME, MA, MI, MN, MO, NH, NY, ND, OR, RI, SD, UT, VT, WA, WI and WY or "Zone C." In the event of a crash necessitating deployment of the passenger frontal air bag, these passenger air bag inflator may explode due to propellant degradation occurring after long-term exposure to absolute humidity and temperature cycling.

Consequence & remedy

Consequence: An inflator explosion may result in sharp metal fragments striking the driver or other occupants resulting in serious injury or death.

Remedy: MBUSA will notify owners, and dealers will replace the passenger frontal air bag module, free of charge. Mercedes issued an interim notification to owners on February 23, 2018. A second notice will be mailed when remedy parts are available. Owners may contact MBUSA customer service at 1-877-496-3691.

16V363000 · Air Bags:frontal:passenger Side:inflator Module

May 26, 2016

Mercedes-Benz USA, LLC (MBUSA) is recalling certain model year 2008-2011 C300 Sedan, C300 4matic Sedan, C350 Sedan, C63 AMG Sedan vehicles, 2010-2011 GLK350, GLK350 4-Matic and E350 Coupe vehicles, 2011 SLS AMG, E350 Convertible, E550 Coupe and E550 Convertible vehicles originally sold, or ever registered, in Alabama, California, Florida, Georgia, Hawaii, Louisiana, Mississippi, South Carolina, Texas, Puerto Rico, American Samoa, Guam, the Northern Mariana Islands (Saipan), and the U.S. Virgin Islands, or "Zone A." Additionally, unless included in "Zone A" above, MBUSA is recalling certain model year 2008 C300 Sedan, C350 Sedan, C63 AMG Sedan and C300 4-Matic Sedan vehicles originally sold, or ever registered, in Arizona, Arkansas, Delaware, District of Columbia, Illinois, Indiana, Kansas, Kentucky, Maryland, Missouri, Nebraska, Nevada, New Jersey, New Mexico, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Virginia, and West Virginia, or "Zone B." Vehicles not originally sold or ever registered in either Zones A or B are not subject to this safety recall. These vehicles are equipped with certain air bag inflators assembled as part of the passenger frontal air bag modules, and used as original equipment or replacement equipment. In the event of a crash necessitating deployment of the front air bags, these inflators may rupture due to propellant degradation occurring after long-term exposure to absolute humidity and temperature cycling.

Consequence & remedy

Consequence: An inflator rupture may result in metal fragments striking the vehicle occupants resulting in serious injury or death.

Remedy: MBUSA will notify owners, and dealers will replace the passenger frontal air bag modules, free of charge. Owners were sent an interim notification October 2016. A second notice will be mailed when remedy parts are available. Owners may contact MBUSA customer service at 1-877-496-3691.

16V081000 · Air Bags:frontal:driver Side:inflator Module

Feb 11, 2016

Mercedes-Benz USA, LLC. (MBUSA) is recalling certain model year 2009-2010 ML320 BlueTec 4Matic, GL320 BlueTec 4Matic and R320 CDI 4Matic, 2011 E350 Cabriolet and E550 Cabriolet, 2009-2011 ML350, ML350 4Matic, ML550 4Matic, ML63 AMG, and C63 AMG, 2010-2011 ML450 4Matic Hybrid, E350 Coupe, E350 4Matic, E550 Coupe, E550 4Matic, and E63 AMG, 2011-2012 GL350 BlueTec 4Matic and R350 BlueTec 4Matic, 2009-2012 GL450 4Matic, GL550 4Matic and R350 4Matic, 2007-2008 SLK280, SLK350, and SLK55 AMG, 2011-2014 SLS AMG Coupe, 2012 SLS AMG Cabriolet, 2013-2014 SLS AMG GT and SLS AMG GT Cabriolet, 2005 C230 Kompressor and C320, 2006-2007 C230, 2006-2011 C350, 2008-2011 C300 and C300 4Matic, 2010-2012 GLK350 and GLK350 4Matic and 2007-2008 Chrysler Crossfire vehicles. Upon deployment of the driver's frontal air bag, excessive internal pressure may cause the inflator to rupture.

Consequence & remedy

Consequence: In the event of a crash necessitating deployment of the driver's frontal air bag, the inflator could rupture with metal fragments striking the driver or other occupants resulting in serious injury or death.

Remedy: MBUSA will their notify owners, and Fiat Chrysler will notify the affected Chrysler owners. Dealers for the respective brands will replace the driver's frontal air bag module, free of charge. This recall began November 2016. Mercedes-Benz owners may contact MBUSA customer service at 1-800-367-6372 and Chrysler owners may contact Fiat Chrysler customer service at 1-800-853-1403.

15V711000 · Air Bags:frontal:sensor/control MODULE-INACTIVE

Oct 27, 2015

Mercedes-Benz USA, LLC. (MBUSA) is recalling certain model year 2008-2009 C300 Sedan, C300 4Matic, C63 AMG, and C350 vehicles, and 2010 GLK350 and GLK350 4Matic vehicles. Due to a manufacturing error, the air bag control unit may corrode and cause the control unit to malfunction.

Consequence & remedy

Consequence: The malfunctioning air bag control unit may cause the air bags to unexpectedly deploy increasing the risk of injury and the possibility of a vehicle crash. Alternatively, the air bag control unit malfunction may cause the air bags to not deploy in the event of a crash necessitating air bag deployment, increasing the risk of occupant injury.

Remedy: MBUSA will notify owners, and dealers will inspect the air bag control unit and replace it, as necessary, free of charge. Mercedes-Benz issued an interim notification to owners on December 23, 2015. The recall began on March 14, 2016. Owners may contact MBUSA customer service at 1-800-367-6372.

Model-level recall history does not show whether a particular VIN is affected or has received a repair. Check a VIN with NHTSA ↗

NHTSA investigations

1

EA21002 · Desiccated Air Bag Inflator Rupture

Opened Sep 17, 2021 · No close date supplied

Status: open (inferred from source dates) · Air Bags:frontal:driver Side:inflator Module; Air Bags:frontal:passenger Side:inflator Module

From 2000 through 2017, Takata produced millions of air bag inflators using two types of phase-stabilized ammonium nitrate ("PSAN") propellant -- propellant 2004 and propellant 2004L. After prolonged exposure to high temperature cycles and humidity, inflators using propellant 2004 can degrade, causing the propellant to burn too quickly when ignited. The rapid burning can cause the inflator to rupture during deployment, potentially causing serious or even fatal injury to vehicle occupants. See 2016 Blomquist Report at www.nhtsa.gov/sites/nhtsa.gov/files/documents/expert_report-hrblomquist.pdf.Consequently, all frontal inflators using propellant 2004 that do not contain a "desiccant" (a substance that traps and holds moisture) in US vehicles are under recall. These "non-desiccated" inflators either have been or are required to be replaced.In some cases, the remedy part for these recalled inflators was, or will be, an inflator using either propellant 2004 or 2004L that does contain a desiccant. None of these "desiccated" remedy parts (which were installed in older model year vehicles) are currently under recall for a degradation concern. Certain subsets of desiccated PSAN inflators using propellant 2004 for use as original equipment, however, have been recalled for a degradation concern. All Takata inflators produced with propellant 2004L contain desiccant, and none of these desiccated inflators using propellant 2004L are under recall for a degradation concern. There have been no reported field ruptures in any non-recalled desiccated PSAN inflators.It is understood that desiccants fully saturate at some threshold, at which point any additional moisture will not be captured. This means the degradation process observed in non-desiccated inflators using propellant 2004 may also occur in non-recalled desiccated inflators using propellant 2004, assuming additional moisture enters the inflator and high temperature cycling occurs. Based on available information, desiccant saturation can occur within the first five years in the worst environments, and the time required for full saturation is affected by multiple factors. While no present safety risk has been identified, further work is needed to evaluate the future risk of non-recalled desiccated inflators using propellant 2004.Three entities -- Takata (now known as TK Global), the Independent Testing Coalition, and Exponent -- have been studying the long-term behavior of Takata desiccated PSAN inflators using propellant 2004L (as well as 2004) in the presence of moisture and temperature cycling. The research efforts, which include development of predictive modeling techniques and field sample analysis, are ongoing. To date, none of the researchers have identified field evidence showing that propellant 2004L is undergoing a degradation process that leads to aggressive deployment and potential rupture. However, the time in service of such inflators remains short compared to that of the inflators using propellant 2004. Further study is needed to assess the long-term safety of desiccated inflators using propellant 2004L.The Office of Defects Investigation is opening this investigation to examine whether a safety defect related to propellant degradation exists in non-recalled desiccated PSAN frontal inflators manufactured by Takata. This investigation will require extensive information on Takata production processes and surveys of inflators in the field. Lists of recall actions that may have used desiccated PSAN inflators as remedy parts, as well as the makes and models originally manufactured with them, is available with the downloadable version of this document (see nhtsa.gov/recalls?nhtsaId=EA21002 -- note this information is subject to change/revision as the investigation proceeds). This investigation does not supersede EA15-001, which remains open.

Additional source detail variants (2)

Air Bags:frontal:driver Side:inflator Module

From 2000 through 2017, Takata produced millions of air bag inflators using two types of phase-stabilized ammonium nitrate ("PSAN") propellant -- propellant 2004 and propellant 2004L. After prolonged exposure to high temperature cycles and humidity, inflators using propellant 2004 can degrade, causing the propellant to burn too quickly when ignited. The rapid burning can cause the inflator to rupture during deployment, potentially causing serious or even fatal injury to vehicle occupants. See 2016 Blomquist Report at www.nhtsa.gov/sites/nhtsa.gov/files/documents/expert_report-hrblomquist.pdf.Consequently, all frontal inflators using propellant 2004 that do not contain a "desiccant" (a substance that traps and holds moisture) in US vehicles are under recall. These "non-desiccated" inflators either have been or are required to be replaced.In some cases, the remedy part for these recalled inflators was, or will be, an inflator using either propellant 2004 or 2004L that does contain a desiccant. None of these "desiccated" remedy parts (which were installed in older model year vehicles) are currently under recall for a degradation concern. Certain subsets of desiccated PSAN inflators using propellant 2004 for use as original equipment, however, have been recalled for a degradation concern. All Takata inflators produced with propellant 2004L contain desiccant, and none of these desiccated inflators using propellant 2004L are under recall for a degradation concern. There have been no reported field ruptures in any non-recalled desiccated PSAN inflators.It is understood that desiccants fully saturate at some threshold, at which point any additional moisture will not be captured. This means the degradation process observed in non-desiccated inflators using propellant 2004 may also occur in non-recalled desiccated inflators using propellant 2004, assuming additional moisture enters the inflator and high temperature cycling occurs. Based on available information, desiccant saturation can occur within the first five years in the worst environments, and the time required for full saturation is affected by multiple factors. While no present safety risk has been identified, further work is needed to evaluate the future risk of non-recalled desiccated inflators using propellant 2004.Three entities -- Takata (now known as TK Global), the Independent Testing Coalition, and Exponent -- have been studying the long-term behavior of Takata desiccated PSAN inflators using propellant 2004L (as well as 2004) in the presence of moisture and temperature cycling. The research efforts, which include development of predictive modeling techniques and field sample analysis, are ongoing. To date, none of the researchers have identified field evidence showing that propellant 2004L is undergoing a degradation process that leads to aggressive deployment and potential rupture. However, the time in service of such inflators remains short compared to that of the inflators using propellant 2004. Further study is needed to assess the long-term safety of desiccated inflators using propellant 2004L.The Office of Defects Investigation is opening this investigation to examine whether a safety defect related to propellant degradation exists in non-recalled desiccated PSAN frontal inflators manufactured by Takata. This investigation will require extensive information on Takata production processes and surveys of inflators in the field. Lists of recall actions that may have used desiccated PSAN inflators as remedy parts, as well as the makes and models originally manufactured with them, is available with the downloadable version of this document (see nhtsa.gov/recalls?nhtsaId=EA21002 -- note this information is subject to change/revision as the investigation proceeds). This investigation does not supersede EA15-001, which remains open.

Air Bags:frontal:passenger Side:inflator Module

From 2000 through 2017, Takata produced millions of air bag inflators using two types of phase-stabilized ammonium nitrate ("PSAN") propellant -- propellant 2004 and propellant 2004L. After prolonged exposure to high temperature cycles and humidity, inflators using propellant 2004 can degrade, causing the propellant to burn too quickly when ignited. The rapid burning can cause the inflator to rupture during deployment, potentially causing serious or even fatal injury to vehicle occupants. See 2016 Blomquist Report at www.nhtsa.gov/sites/nhtsa.gov/files/documents/expert_report-hrblomquist.pdf.Consequently, all frontal inflators using propellant 2004 that do not contain a "desiccant" (a substance that traps and holds moisture) in US vehicles are under recall. These "non-desiccated" inflators either have been or are required to be replaced.In some cases, the remedy part for these recalled inflators was, or will be, an inflator using either propellant 2004 or 2004L that does contain a desiccant. None of these "desiccated" remedy parts (which were installed in older model year vehicles) are currently under recall for a degradation concern. Certain subsets of desiccated PSAN inflators using propellant 2004 for use as original equipment, however, have been recalled for a degradation concern. All Takata inflators produced with propellant 2004L contain desiccant, and none of these desiccated inflators using propellant 2004L are under recall for a degradation concern. There have been no reported field ruptures in any non-recalled desiccated PSAN inflators.It is understood that desiccants fully saturate at some threshold, at which point any additional moisture will not be captured. This means the degradation process observed in non-desiccated inflators using propellant 2004 may also occur in non-recalled desiccated inflators using propellant 2004, assuming additional moisture enters the inflator and high temperature cycling occurs. Based on available information, desiccant saturation can occur within the first five years in the worst environments, and the time required for full saturation is affected by multiple factors. While no present safety risk has been identified, further work is needed to evaluate the future risk of non-recalled desiccated inflators using propellant 2004.Three entities -- Takata (now known as TK Global), the Independent Testing Coalition, and Exponent -- have been studying the long-term behavior of Takata desiccated PSAN inflators using propellant 2004L (as well as 2004) in the presence of moisture and temperature cycling. The research efforts, which include development of predictive modeling techniques and field sample analysis, are ongoing. To date, none of the researchers have identified field evidence showing that propellant 2004L is undergoing a degradation process that leads to aggressive deployment and potential rupture. However, the time in service of such inflators remains short compared to that of the inflators using propellant 2004. Further study is needed to assess the long-term safety of desiccated inflators using propellant 2004L.The Office of Defects Investigation is opening this investigation to examine whether a safety defect related to propellant degradation exists in non-recalled desiccated PSAN frontal inflators manufactured by Takata. This investigation will require extensive information on Takata production processes and surveys of inflators in the field. Lists of recall actions that may have used desiccated PSAN inflators as remedy parts, as well as the makes and models originally manufactured with them, is available with the downloadable version of this document (see nhtsa.gov/recalls?nhtsaId=EA21002 -- note this information is subject to change/revision as the investigation proceeds). This investigation does not supersede EA15-001, which remains open.