What are OSHA requirements for lockout/tagout?

While considering a premium adjustment, our insurance company recently sent a representative to review safety procedures at our facilities. During the review, the representative said the OHSA lockout/tagout requirements we follow for maintaining our facility’s equipment also applies to vehicles in the shop. Our technicians keep the keys with them while working on a truck, but the insurance representative is recommending a review of our processes and believes we may need additional measures in place. Can you please help with our understanding of these requirements?