General Motors Co. said it will make modifications to the Chevrolet Volt after a series of fires occurred following test crashes of the plug-in hybrid vehicle.

GM said the fires were caused by a coolant leak that occurred when the battery pack in the vehicle was punctured during the tests of severe side crashes by the National Highway Traffic Safety Administration. The fires occurred hours to weeks after the tests as the coolant leaked and eventually created a short circuit.

The automaker will add structural reinforcement that better protects the battery pack from puncture or a coolant link in a severe side crash, said Mary Barra, GM’s senior vice president of global product development.

It will also add a sensor in the reservoir of the battery coolant system to monitor coolant levels and add a tamper-resistant bracket to the top of the battery coolant reservoir to help prevent potential coolant overfill.


Additionally, technicians will drain batteries of their charge following severe crashes. The fix will add about three pounds to the weight of the vehicle.

GM said it has conducted four successful crash tests between Dec. 9 and 21 of Volts with the modifications and that there were no intrusions into the battery pack and no coolant leakage in any of the tests.

The automaker will call back about 8,000 Volts already in customer hands and make the changes in February. Additionally it will have to modify about 4,400 cars in dealer inventories and is making changes in its assembly line so that newly produced vehicles contain the reinforcement.

Barra said that Volts have been driven a combined 20 million miles since their introduction in late 2010 and that there have been no fires similar to what occurred in the NHTSA tests.


NHTSA said it crashed a Chevy Volt retrofitted with GM’s reinforcement device and that there was no penetration of the vehicle’s battery compartment and “that no coolant leakage was apparent.” The safety agency said it plans to monitor the vehicle for another week as a precaution, but that the preliminary result of the crash test indicates that GM’s remedy “should address the issue of battery intrusion.”

The agency said it will make public its final conclusions in the coming weeks.

GM has offered to buy back the car or provide free loaner vehicles if owners are concerned about the safety of their Volts. Only 250 have requested a buy-back or loaner vehicle, Mark Reuss, president of GM North America.

The car, as well as other electric vehicles, have not been brisk seller. GM has sold about 8,000 Volts, which can travel about 40 miles just on battery power before a gas engine kicks in and functions as a generator to extend the range an additional 300 miles. Nissan, by comparison, has sold just about 10,000 of its Leaf electric vehicle.


NHTSA launched a formal safety-defect investigation into the car last year after crash tests on several Volts and their batteries resulted in fires. In one case, a fire that started in one of the test vehicles consumed three others parked nearby.

But the fires did not occur during the actual crashes. NHTSA subjected three Volt batteries to a crash simulation, intentionally damaging the cars’ battery compartment and rupturing their coolant lines. One battery caught fire about a week after the test. A second vehicle’s battery “began to smoke and emit sparks” just hours after the impact, the agency said. One car caught fire three weeks after the crash.

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