So far--the responses in this thread have touched on addressing several potential "profit soft spots" related to productivity:
appropriate pricing for diagnostic/ up-front work (i. e. making sure the shop can cover its costs) (diagnostic pricing recommendation, offered by Tony M, Baldwin Express Lube);
cutting down the transition time between performing the (small-revenue) diagnostic work, and performing the associated (larger-revenue) maintenance work (add a service writer recommendation, offered by Joe M, Osceola);
improving the clarity and precision with which "diagnostic findings" get translated into a job estimate that a customer wants to buy (service writer rec, Joe);
Beyond the suggestions above, and improving the "on the job" productivity of the technician individually - it is worthwhile for you as a shop owner/ business manager to look at what I'd call the "white space" around the direct work on the car. This "white space" is defined as "space where low/ no value is being created"--for you or the customer. Some examples of white space that you might want to think creatively about addressing include:
the car-movement/ parking issues around your shop (if your techs are moving cars, they're not contributing positively to productivity);
the time you spend going back/ forth with customers on the phone, trying to communicate the details of an estimate, and discover if the customer wants to go forward with it;
the ways that you structure your parts/ equipment inventory (if your techs need to search for tools, equipment, or parts, or walk too far to get them, they're not contributing positively to productivity);
the precision/ detail with which your tech's diagnostic findings--or other observations about the "street-readiness" of the customer's vehicle) get translated into an estimate the customer wants to buy;
... and others.
These and other white-space examples can all be forms of "waste". Some of the highest value opportunities in your business can be removing these types of barriers to productivity, to help you create more satisfied customers, and earn more money.