With no continually-running internal combustion engine, traditional gearbox or clutch, electric cars are impossible to stall. When the car comes to a halt for a stop light or intersection, the electric motor stops too, meaning there’s no possibility of a stall — at least under normal operating procedure.
Yet as German automaker Volkswagen quietly announced at the start of this month, some 5,561 2015 through 2016 model year Volkswagen e-Golfs are being recalled to rectify a problem with their on-board power electronics which mimics a traditional internal combustion engine stall perfectly. Noticed by CNET earlier this week, the recall — which was officially announced earlier this month — concerns the battery management system on Volkswagen e-Golf electric cars made between May 21, 2014 and March 1, 2016.
As the name suggests, the job of the battery management system (BMS)on an electric car is to ensure that the car’s high-voltage, high-capacity traction battery pack is kept healthy and happy at all times. In addition to ensuring the battery pack is charged properly and constantly monitoring the health of each cell (or module of cells) in the battery pack, the BMS also watches for unusual spikes in current in and out of the battery pack. If the current gets unusually high or there’s some other current or voltage spike, the BMS can shut off the main traction pack contactor (essentially a large relay or pair of relays) to break the electronic circuit and ensure no harm comes to either the car or the battery pack.
Like a circuit breaker tripping in your home, the only way to ensure power can flow again — and the car can operate — is to reset the system. In the case of an electric car, that means stopping, turning the car off — and then turning it on again.
As documents submitted by Volkswagen to the U.S. National Highway Traffic Safety Administration show, affected Volkswagen e-Golfs feature an over-sensitive BMS system which are essentially operating on something of a hair-trigger, interpreting the brief electrical current surge that accompanies hard acceleration from standstill or the start of heavy regenerative braking as being an unacceptable and damaging current surge in the battery pack. This causes the car to trigger an error state which disconnects the main power contactors and cuts all power to the car’s power electronics.
Likened to a stall, this sudden lack of power can increase the risk of a crash, although Volkswagen notes that the car’s power steering system, brakes and emergency systems — as well as the usual lights and infotainment systems — remain functional when this state is triggered since they all operate off the car’s 12-volt accessory circuits.
The recall is believed to have been triggered by a series of complaints made to NHTSA by Volkswagen e-Golf owners, in which customers detail the sudden and unexpected loss of power as a consequence of the error. In total, seven complaints have been logged on NHTSA’s website, with the first logged in September last year, although many more Volkswagen e-Golf customers appear to have been affected by the same problem.
In situations where a BMS error has caused an electric car to cut power to its drivetrain, the standard response — as is the case with any malfunctioning electronic device — is to execute a power cycle (otherwise known as turning it off and then on again.) But while some Volkswagen e-Golf owners report they were able to get their cars working again after executing a power cycle, far more report that their car remained unresponsive and unable to move after the error was triggered.
“An error popped up on the dash screen saying ‘Error: Electrical System. Stop!,'” said one complainant. “Efforts to restart the car (turning it off and on) were unsuccessful.” While the owner in this particular case reports that they were able to coast their car to the side of the road to safety, others report their cars left them stranded in the middle of parking lots and fast-moving roads.
Despite some owners being left in precarious situations, no injuries or deaths have occurred as a result of this fault.
To rectify the situation, Volkswagen will offer owners of affected cars a complementary reprograming of their car’s BMS system with new, refined code that should prevent the car from misinterpreting everyday actions as a dangerous sudden current event. As with all official recalls, customers will be contacted by Volkswagen in the coming weeks to arrange an appointment at a local e-Golf dealership for the reprogramming to take place.
In the meantime, concerned customers can find out more information about the recall by calling NHTSA’s specialized recall line on 1-888-327-4236 (TTY 1-800-424-9153), or by visiting www.safercar.gov. Alternatively, they can reach Volkswagen’s customer service department directly on 1-800-953-5298.
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