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Editor’s Note: This blog has been updated to reflect the software update recall initiated by Mercedes-Benz and posted by NHTSA on Jan. 10, 2022.

In August, the National Highway Traffic Safety Administration (NHTSA) opened a rollaway investigation into the Mercedes Sprinter vans with e-shifters that automatically move the transmission into Park when the driver leaves the seat. Used by Amazon’s delivery service providers, these vans have been sprinting away – with the shift indicator showing Park, and sometimes with the parking brake applied, too. Just before Christmas, Mercedes delivered a temporary fix with a Grinch-y rant against drivers. But, the preliminary evidence points to a long-established mechanical source of rollaway – a defective park pawl. Blame the driver is the manufacturers’ rollaway go-to, but will it make the investigation go away?

In 2021, Amazon Logistics – the fulfillment arm of the online retail behemoth – delivered more packages than FedEx – 4.2 billion parcel shipments in 2020, according to an analysis by Pitney Bowes. And all those billions of dish racks, books, clothing, 50-lb. bags of dog food – and every other household necessity, personal obsession, and impulse purchase – reaches America’s front doors via an army of drivers manning Amazon’s fleet, consisting mostly of Mercedes Sprinter vans.

By all accounts, the life of an Amazon delivery person is short and brutish, composed of 10-hour shifts humping as many as 40 packages an hour, while an Android device called a “rabbit” maps your route and tracks your execution to ensure that you are keeping up the pace. A December 2020, first-person, day-in-the-life-of-an-Amazon-delivery-driver story published by Business Insider, reported that a driver gets in and out of that van 200 times a day. A Reddit forum for Amazon drivers paints a fairly miserable picture of the experience – low pay, zero respect and push-to-the-breaking-point level of productivity expectations – which is apparently why the position has such high turnover.

Given the number of stops a day a driver must make and the relentless pace of delivery, Amazon needed a van that would provide good protection against rollaway, the long-time safety hazard of unintended movement in a vehicle with no driver. Rollaways can occur when the engine is on, or off, and can be caused by mechanical and software failures, or by design-induced human error.

The 2019 Mercedes Sprinter van appeared to deliver – with an electronic shifter that provides one of the most comprehensive automatic shift-to-Park algorithms The Safety Record, which has pored over scores of service literature and owner’s manuals, and examined dozens of vehicles, has ever seen. (We’ll get to that in a moment) An electronic shifter replaces the mechanical connection between the gear selector and the transmission with software that sends electronic signals from the gear selector interface to an electronic control module which relays the request to the transmission. In a 2019 Mercedes Sprinter, the shifter is a steering column mounted stalk behind the steering wheel that is pressed up or down, depending on the gear. Park is a button on the end of the lever.

Mercedes Sprinter vans – particularly in the 2019 model year – were rolling away with enough regularity to catch the attention of the National Highway Traffic Safety Administration’s (NHTSA) Office of Defects Investigation (ODI).

In early August, ODI opened a Preliminary Evaluation of 19,000 2019 Mercedes Sprinter vans. The Opening Resume described the potential defect as: “MY 2019 Mercedes-Benz Sprinter 2500/3500/4500 vans, configured for use as Amazon delivery vehicles or ambulances, roll away shortly after being shifted to Park using the Auto-P function.” The investigation is based on 11 consumer complaints in NHTSA’s Vehicle Owner’s Questionnaire (VOQ) database, representing eight crashes and one injury. A broader search turns up a total of 19 such reports. They have narratives like these:

The delivery driver placed the van in park on a hill and engaged the emergency parking brake.  While the engine was still running the delivery driver took a minute or two to locate his package and proceeded to step out of the driver door while the van was still running.  Just as he was stepping out of the van the driver heard several loud clicks and the van proceeded roll away and was stopped by a large tree branch that caused damage to the roof of the van.  I have had several of these vans roll away some causing significant damage to the vans, other people’s property and 2 drivers have been hurt as a direct result of this same problem.

Here’s another, with a more serious outcome:

The contact’s client was utilizing a 2019 Mercedes- Benz Sprinter 2500 for work. The contact stated while the vehicle was in park, the driver exited the vehicle however, it rolled backward, flipped over, and crushed the driver’s legs. There were no warning lights illuminated. The driver sustained road and chemical burns and medical attention was provided.  A police report was filed. There was no report of a fire or airbag deployment. The vehicle was towed to an independent lot. The local dealer was not contacted. The vehicle was not diagnosed or repaired. The manufacturer was notified of the failure and inspected the vehicle where the black box was retrieved. The contact mentioned referenced NHTSA Action Number PE21019 (Power train). The failure mileage was 965.

Or, if you prefer, you can watch a typical incident:

Rollaway is a longstanding, and diverse problem — recalls and investigations going back to the 1970s show that the root causes range from broken parts, like pawls and rods, to the effect of new technologies, such as keyless ignitions and new electronic transmission gear shift designs, on driver behavior. In the last several years, The Safety Record has been reporting on this safety problem and the solutions – you can read about them here:  

Technology Has Made Rollaways Easier: Technology Can Prevent Them

The 2019 Sprinter, a vehicle predominantly used by delivery expeditors, is the first model year of the third generation of the van, and the first year to use the e-shifter, a design found on many other Mercedes models. In 2018, Amazon announced that it had ordered 20,000 Mercedes-Benz Sprinter vans that would be leased by its Delivery Service Partners – a program for small business owners to deliver packages ordered through Amazon. Amazon Sprinter vans have an auto-shift-to-park function that automatically moves the electronic shifter to the Park position, if the driver attempts to exit without first securing Park, regardless of whether the engine is on or off. Auto-shift-to-Park features first emerged as a safety measure on passenger vehicles with e-shifters that used non-standard shift controls – like buttons, rotary knobs, and Monostable stick selectors that always return to the center position after gear selection. These new shifter designs lack the mechanical detents and consistent PRNDL sequence that most drivers were used to. This has led to drivers misjudging the gear position and exiting the vehicle without securing it in Park, followed by NHTSA investigations and recalls to implement a failsafe, such as an automatic shift-to-park feature.

Further, if the Sprinter van is not in Park and the driver opens the door, or unbuckles the seat belt or gets out of the seat, the e-shifter moves to Park. That covers all of the components of driver exit. That last condition – driver leaves seat – is determined by a driver seat occupant detection sensor, a design feature that is atypical for in these designs. While Automatic shift-to-park features in the U.S. fleet work under a variety of conditions – some only activate if the driver has turned the engine off, some don’t work if the transmission is in Neutral. Most use the combination of seatbelt unbuckled, no brake application, and the driver’s door open as the markers for driver exit. But, the Sprinter design with its driver occupant detection sensor as the trigger seems to acknowledge the realities of an Amazon delivery driver’s day.  

The Sprinter is also available with an optional Electronic Parking Brake (EPB). EPBs are an increasingly common feature that can be configured to automatically activate under whatever conditions the automaker chooses. Again, some only activate when the engine is turned off, or when the brake hold mode is manually activated, a convenience feature that holds the vehicle at a temporary stop – like a traffic light – without requiring the brake pedal to be depressed, and then releases when the accelerator is depressed to resume travel. Other manufacturers automatically apply the EPB to prevent rollaway. For example, 2014 model year Jeep and Chrysler models added “Safehold” that will engage the EPB automatically if the transmission is not in Park, the seat belt is unbuckled, the service brake is not applied and the driver’s door is opened. The commercial version of the 2019 Ram ProMaster 2500 van, a rebadged Mercedes Sprinter – also used as Amazon delivery vans – have a mechanical shift lever and an automatically applied EPB. Others with auto-applied EPBs include Ford, GM, Volvo and Mercedes – in other models.

The Amazon-configured vans have an old-school hand-operated mechanical parking brake.

So how is this happening? Drivers are reporting that the transmission was in park, and some maintained that they pulled the mechanical parking brake lever, too. Despite Mercedes’ thoughtful approach to rollaway prevention using vehicle electronics, the problem appears to lie with its mechanical components. According to David Bizzak, a Monroeville, PA-based mechanical engineer who has examined the failure mechanism in several Sprinters, the park pawl, which locks the transmission to prevent vehicle movement doesn’t consistently maintain engagement in the ring gear. This design was intended for use on lighter vehicles, but the heavier Sprinter vans appear to put greater forces on the tapered park pawl, and that added friction can force the pawl out of engagement when under load.

“This transmission has been used in Mercedes’ car line for many years, and to our knowledge there isn’t a rollaway issue with their passenger cars,” Bizzak says. “We believe it may be possible that the heavier weight of the Sprinter van creates a situation in which this disengagement of the park pawl can occur.”

In addition, says Bizzak, the parking brake requires a lot of clicks – like 10 – before it is fully engaged.

It’s difficult to know where NHTSA’s investigation is at. The only documents in the public file are the Opening Resume, and an information request to Mercedes, asking for things like its communications with Amazon, and an explanation why FedEx, which also uses Sprinters, is not having the same problem. We do know that NHTSA was present at an inspection that Bizzak also attended in April 2021 where this park pawl problem became evident.

In the meantime, on December 15, Mercedes filed a recall Part 573 Notice of Defect and Noncompliance report in which it blamed a rare condition it calls a “park lock system error” that could only result in a rollaway if the driver does not put the vehicle transmission in Park and set the manual parking brake. (NHTSA acknowledged the recall on January 7.)  The remedy involves installing revised software in the ESP control unit on the recall population.

The defect could affect as many as 48,000 of 2019 to 2021 Mercedes and Freightliner Sprinter vans, built on Platform 907, between June 05, 2018 and November 30, 2020 with a manual parking brake and a 7-speed automatic transmission that was manufactured between May 1, 2018 and October 31, 2019 in the Hedelfingen transmission plant in Germany. How many out of the 48,000 are so afflicted? Mercedes guesses it’s at 1 percent.

Mercedes mentions two problems: A “rare and temporary park lock function error” it identified during testing, and it “a separate factor” that can contribute to the park lock function error “or enhance the related rollaway risk: the ‘Park Lock Support’ (‘PLS’) function.” The PLS is part of the ESP Control Unit, not the transmission, which “applies continued brake pressure after the vehicle is stopped and the gear selector is placed in ‘P.’” Mercedes could not isolate that cause of the failure, “despite its intensive investigation, multifaceted testing, analyses, and evaluation.”

The PLS applies brake pressure after the transmission is put into Park, so it almost functions like an automatically applied electronic parking brake. The recall notice does not explain how long the PLS is active after putting the transmission into Park, or why it is even necessary for the vehicle to apply hydraulic brake pressure after the driver or the vehicle automatically shifts into Park.    

Or maybe, the PLS is more like a brake hold or hill hold – driver convenience features found on many vehicles – which, if activated, allow the driver to take their foot off the brake while at a temporary stop, like at a traffic light or on an incline. Brake Hold / Hill Hold features apply  hydraulic brake pressure to the wheels and typically release when the driver depresses the accelerator pedal and resumes travel. Brake Hold / Hill Hold systems requires a running engine to power the hydraulic brake pressure; it is meant to be temporary, and in most vehicles with the feature, the Brake Hold mode only lasts between three and 10 minutes. In many vehicles with an electronic parking brake, the Brake Hold / Hill Hold will automatically apply the EPB after a specified time period, to hold the vehicle in place, or if the driver shuts off the engine and attempts to leave the vehicle while it is being held stationary in Brake Hold Mode.

In either case, Mercedes is doesn’t disclose how it’s resetting the PLS parameters, but the essence of the system suggests that it is creating an EPB-like system using the hydraulic brakes to ensure that the vehicle will remain stationary for some unspecified time – likely the amount of time it takes an Amazon delivery person to hop out of the van, deposit a package on the doorstep and be on the way to the next stop.

The Safety Record has questions why these specific vehicles and these specific transmissions? Had Mercedes already implemented a mechanical or software fix to prevent these rollaways in the vans after Nov. 30, 2020, without filing a Part 573 within five days of deciding that there was a problem with the 2019s?    

Mercedes maintains that the driver has to follow “parking instructions” – in other words, put the transmission into park and get all 10 clicks on the parking brake lever to prevent a rollaway. Why does it matter whether the driver or the vehicle shifts the transmission into Park? According to the Mercedes service description, the Park Lock function is agnostic on the subject of how the Park position is achieved:

The park pawl is used as an additional safety feature for the parking brake and its purpose is to secure the vehicle to prevent it from rolling away inadvertently. 

The park pawl essentially consists of the parking lock mechanism and the electrohydraulic components located at the rear of the transmission housing. There is no mechanical connection whatsoever between the park pawl components of the automatic transmission and the DIRECT SELECT lever (S16/13) (“Park-by-Wire”).

The park pawl is engaged and disengaged purely by electrohydraulic means, either by operating the DIRECT SELECT lever or depending on various factors such as opening the driver’s door whilst the drivetrain is operational.

Is it really the application of the mechanical parking brake that would prevent the rollaways? Is it realistic to think that Amazon deliverers will take the time to set the parking brake scores of times a day with enough force to hold the vehicle and without running afoul of the rabbit on their phones? Why did Mercedes bother with such a comprehensive auto-park algorithm? If the parking brake is the primary park feature, why is this manual design used rather than an EPB that can ensure full clamp load and provide automatic application?

A week later, Mercedes issued a temporary fix and “an important safety reminder.” The former is an update to the PSM module which would sound a horn if the driver leaves the seat without the parking brake engaged. Mercedes says this was tested on some fleet vehicles and is effective.

The latter is one of the nastier blame- the-driver statements we have seen from a manufacturer – and we’ve seen a few. For example, in the late 1970s to early1980s, Ford JATCO transmissions that were experiencing Park-to-Reverse were linked to 306 deaths. In 1977, NHTSA initiated the first of several investigation into the root causes. It found two design flaws and evidence that Fords were at least 12 times more likely to experience Park-to-Reverse than GM or Chrysler vehicles. Ford denied that there was any technical or mechanical defect, and placed the blame on drivers:

…Ford has submitted data to NHTSA data, views, and arguments to establish that no such defect exists. Ford believes that these submissions demonstrate that unexpected vehicle movement is the result of drivers’ inadvertent misplacement of the gear selector lever, can and does occur, though rarely, on all manufacturers’ automatic transmission-equipped vehicles, and is not attributable to any defect in the vehicle design or construction. When unexpected vehicle movement incidents do occur, as they can on any automatic transmission-equipped vehicle, serious consequences may result. Ford believes, however, that such incidents can be avoided if before leaving the driver’s seat, all drivers observe three commonsense steps to make sure the vehicle is securely immobilized. These steps are: 1) properly engaging the transmission system in “park,” 2) setting the parking brake, and, 3) shutting off the engine.

More recently, Chrysler took a swipe at customers who bought one of its products with a Monostable e-shift design. The T-handle style shifter that was located on the center console between the driver and passenger, which looked like a traditional mechanical shift lever, but was activated by depressing a button on the handle and moving the handle rearward or forward – but the handle always returns back the centered/neutral position, which made it easy to misjudge the gear selection.

In April 2016, FCA recalled 811,146 MY 2014-2015 Jeep Grand Cherokees, and 2012-2014 Dodge Chargers and Chrysler 300s, to stave off a NHTSA investigation that was gathering steam.  NHTSA had tested the shifter and found that “the monostable gear selector is not intuitive and provides poor tactile and visual feedback to the driver, increasing the potential for unintended gear selection.” The remedy was the installation of an automatic shift to park feature. The recall notice scolded drivers for failing to heed FCA’s crappy warnings:

FCA US has determined that the existing strategies built into these vehicles to deter drivers from exiting the vehicle after failing to put the transmission into Park have not stopped some from doing so. Drivers erroneously concluding that their vehicle’s transmission is in the PARK position may be struck by the vehicle and injured if they attempt to get out of the vehicle while the engine is running and the parking brake is not engaged. FCA US has therefore determined that the absence of an additional mechanism to mitigate the effects of driver error in failing to shift the Monostable gear selector into PARK prior to exiting the vehicle constitutes a defect presenting a risk to motor vehicle safety.

Mercedes’ statement is more obnoxious by several orders of magnitude and makes the others look subtle. (Read the entire statement.) Here are some of the best parts:

We note that recently there appear to be drivers of Amazon’s Sprinter fleet who continue to refuse to follow important safety guidelines. Most importantly, each and every time an Amazon Mercedes-Benz Sprinter van is parked, the driver must properly shift the vehicle into “park,” set the parking brake per the instructions in the owner’s manual, and otherwise obey all local laws (e.g., turn the wheels to the curb when parking on an incline, etc.). These rules must be followed every time a Mercedes-Benz Sprinter van is parked — there can be no exceptions. Following these rules is critical to prevent vehicle roll-aways, and the risk of serious personal injury and/or property damage that accompanies them…. we continue to observe instances of drivers buckling their seatbelts improperly, in an effort to try to “trick” the system into thinking the driver is properly using his/her seat belt. For example, seatbelts are pulled behind seats then buckled or otherwise buckled outside of the proper normal fashion around the seat occupant. This not only is illegal under applicable local law, it also is terribly unsafe, and must never occur, as it can result in serious injury.

Mercedes went on to say that it has been begging Amazon to implement this horn honk.

Hmm, why wouldn’t Amazon want their branded delivery vehicles to be honking all the time, waking up napping babies, interrupting Netflix shows and generally annoying their customers? Will Amazon’s drivers follow those safety rules, including setting the manual parking brake every time with enough force to prevent rollaway, while under constant pressure to meet their insane schedules? Videos of these deliveries show that some drivers, racing to meet deadlines don’t close the van door as they dash out to leave a package.

The better question is: Why doesn’t Mercedes put a more robust parking pawl in these delivery vans loaded with packages?

Our mission is providing fact-based research and analysis on injuries associated with product hazards ranging from motor vehicle to consumer and industrial products to medical devices.

We are a small multi-disciplinary team that brings together various and complementary skills. The backgrounds of our staff include careers in safety advocacy, biomechanics and biomedical research, engineering, law, library and information science, and journalism.

Our mission is providing fact-based research and analysis on injuries associated with product hazards ranging from motor vehicle to consumer and industrial products to medical devices. We are a small multi-disciplinary team that brings together various and complementary skills.