System operational theory is key to being able to diagnose any problem. You must understand the system and relationship between systems. I will often tell people to read the system description section before anything technical.

Speaking from personal experience in both being a junior mechanic and senior in guiding a junior... Supervision and instruction. 1st being a guided approach with supervision. Hands on demomstatition and tutoring. Showing a job step by step. This goes with all work types and not just diagnosis. After the hands on guidance continue the supervision but allow the junior the take the lead with the job. Any help in knowledge gaps can be dealt with immediately. Then further with then it can turn to mentorship where a step back can be taken and allow the junior to carry out the work with the welcoming ability to ask for help if needed. I have found mechanics/engineers learn with their hands

Helping junior mechanics improve diagnostics isn’t just about tools—it’s about building confidence and problem-solving skills. In my experience leading technician teams at Ventura Toyota and the Naval Facilities Engineering Systems Command, I’ve found hands-on training, structured troubleshooting, and mentorship to be key. Instead of giving answers, I guide them through their thought process, encouraging critical thinking. Pairing them with experienced techs and reinforcing best practices through training builds their skills. What strategies have you found effective in training junior mechanics?

If I have another mechanic or technician ask me for help with troubleshooting an issue, I start with figuring out what it is they know already. It is important to know their level of understanding so that I know how to approach guiding them to the next steps. Do they understand the system that they are working on, sometimes techs are asked to work on something that they may not have ever seen. Do they have any resources and if not can I provide them with that, old machines notoriously lack technical information. Do they have the fundamental skills required to understand the issue and how to troubleshoot them. Once I know some of these key things, I can tailor my responses to best suit them, I will do what is with in my power to aid them.

Helping a junior mechanic improve diagnostics requires hands-on training, structured guidance, and continuous feedback. Start by pairing them with experienced mechanics for mentorship and real-time learning. Provide step-by-step troubleshooting frameworks and encourage logical problem-solving techniques. Use diagnostic tools and software to enhance their technical skills. Offer practice scenarios, simulations, and workshops to build confidence. Regularly review their progress, highlight strengths, and address weaknesses with constructive feedback. Encouraging curiosity and a problem-solving mindset will accelerate their learning and effectiveness in diagnostics.