Chevrolet announced this morning that they will conduct a “voluntary customer service campaign” to address fire concerns in the Volt extended-range electric car.

Volt owners will receive letters in the mail in February announcing the fix, once parts become available at dealerships. The changes include adding structural reinforcements to the underbody to spread the load of side crashes, thereby reducing the risk of intrusion into the battery pack and its coolant lines. The fix also includes adding a sensor and a tamper-resistant bracket to the coolant reservoir to monitor the coolant level and prevent overfilling.

GM Senior Vice President of Global Product Development Mary Barra says the fire experienced by the National Highway Traffic Safety Administration (NHTSA) occurred because coolant shorted out a printed circuit board in the battery pack when Volts were turned upside down to simulate a rollover after a severe crash test.

Three fires occurred after the NHTSA performed side crash tests into a pole with Volts, and then slowly rotated the cars 360 degrees to simulate a rollover. In the first case that brought the issue to public attention, the fire occurred three weeks after the crash test. In two other cases the fires occurred in a matter of days afterwards. None of the cars caught fire within minutes of the crash tests, and no such incidents have been reported on public roads in what GM says is more than 20 million miles driven thus far by Volt owners.

The upgrade process will take two to three hours at Chevrolet dealerships, and owners will be provided loaner cars while the work is being done, says GM North America President Mark Reuss. New cars produced starting this month will receive the changes on the assembly line, and Chevrolet dealers will upgrade existing in-stock Volts before they are sold.

Reuss says he expects the fixes to address the concern NHTSA is now investigating. NHTSA has not yet announced the measure as a recall.