GM to modify Chevrolet Volts to guard against battery fire

General Motors will add a structural reinforcement and devices to prevent overfilling of the battery cooling system in the Chevrolet Volt hybrid sedan to prevent the possibility of a fire after a side crash.

The changes come seven months after a Volt caught fire three weeks after being crash-tested by the National Highway Traffic Safety Administration. The government agency in November opened a defect investigation into the Volt because of the battery fire.

GM on Thursday said that it will fix about 8,000 Volts now in customers' hands, along with about 4,400 cars that are on dealers' lots or in transit. Repair parts are expected to be available at dealerships in February.

Dealers will need up to three hours to make the fix, GM North America president Mark Reuss said on Thursday in a teleconference with media members. But Volt owners will be encouraged to leave their car with the dealer for the day and will be given a loaner car, Reuss said.

The changes will be added to the Volt production line in suburban Detroit. The plant has been idle for the past few weeks as part of GM's holiday shutdown.

GM said the fix will also be applied to Volts that have been exported and to the Opel Ampera, which is a rebadged and restyled version of the Volt for Europe.

The program is a customer-satisfaction effort, not a government-mandated recall, GM said. NHTSA has not said whether the effort will prompt it to close the Volt investigation.

GM product chief Mary Barra, during Thursday's media teleconference, explained details of the cause of the Volt fire:

-- When the Volt was subjected to a side-impact crash-test, a minor intrusion into the side of the battery pack created an internal coolant leak. GM estimates about one-quarter cup of coolant leaked.

-- NHSTA then subjected the crashed Volt to a rollover test. The test slowly rolled the car for 5 minutes. When the car was inverted during the test more coolant leaked--about 1 quart, GM said. The coolant spilled onto electrical contacts on a circuit board on the top of the battery pack. It was that connection between contacts on the circuit board, along with not discharging the battery pack after the crash test, which led to the fire.

Barra said the structural reinforcement being added to the Volt will more evenly distribute crash forces in a side impact, which will help prevent the intrusion into the battery pack.

Changes to the battery cooling system are the addition of a sensor in the coolant reservoir and a tamper-resistant bracket to prevent the system from being overfilled.

By Dale Jewett