Search for TSBs. Has your car been recalled? Is there a software update for the transmission shudder that the dealer never told you about?
Paying $20 to fix a rattling heat shield feels excessive. Paying $20 to diagnose a P0300 random misfire that saves you a $500 shop diagnostic fee? Priceless. haynes pro free trial
Input the exact OBD-II code your car is throwing. Follow the diagnostic flow chart. Order the specific part it recommends (not just a guess). Search for TSBs
If you are a mobile mechanic, calculate the labor hours for three jobs you have next week. Compare the Haynes Pro time to your actual speed. Adjust your pricing. haynes pro free trial