Spring is here, and the 30-odd Chevy Volt mules have passed through their first winter with flying colors I am told.

GM has tested the cars extensively at the Milford Michigan proving grounds, the Upper Peninsula (UP) of Michigan, and Kapuskasing, Ontario. Ten vehicles visited Kapuskasing and a few visited the upper peninsula.

The focus of the testing at the UP was more for chassis control development including stability control and braking. Battery work was not the primary task, as the lab environment is best for subjecting the battery pack to temperature extremes. Indeed those packs have been undergoing arduous temperature exposures for more than a year, with no problems identified.

In Canada, the focus of the testing was the propulsion system. The cars were kept indoors overnight, and then they were evaluated to see how they started and how they ran after a cold soak.

According to Voltec team leader Greg Ciesel, temperatures the mules were exposed to were "very much below zero," and even at the Milford proving grounds "we got to probably minus 10 or 15 degrees F."

Voltec spokesman Dave Darovitz said "Cold weather vehicle response depends on multiple factors including temperature, battery SOC, battery preconditioning (if plugged in) and if the vehicle was stored inside. Another factor is FMVSS defrost requirements, which demand more heat then we can supply electrically and cause the gas engine to turn on."

He confirmed that testing was successful. "The cars performed as we expected under cold weather conditions," he said "We still have some work ahead of us, but are encouraged with the operating conditions of the mules under very cold conditions."

Volt lead engineer Andrew Farah gave an example of how a certain problem was discovered and fixed during the cold weather testing.. "We ran into some issues, we found out that we had a problem with one of our powertrain mounts," he said "Why, because the car was going though some abusive driving...they told me we broke a mount. We did some analysis and we found things we knew about but we hadn’t gone far enough, it was an 'aha' moment and we fixed it."