The investigation into Chevrolet Volt vehicles could potentially lead to a recall, which might incur costs for GM and affect its brand reputation. However, the immediate market reaction to the news was positive, with GM shares rising. This suggests that investors may not see the investigation as a significant threat to GM's financials or may be focusing on other positive news. The impact is neutral in the short term as the market has already responded positively, but there is a potential downside if the investigation leads to a costly recall.