Although presented here as a step by step process, the overall sequence of a literature search is not linear. It is more of a circular path in which you find some material, read it, then using the information you found, refine your search terms and go back and search again. That circle may need to be repeated more than once for each database and don't forget that the process must be used in every resource that you try.
The process will take time and you'll find that you can't do it all at once. You don't want to waste time repeating work you've already done, so as you go thru the process, keep track of what databases you've searched and what search strategies you've used in each database.
Three different searching strategies are outlined below: Subject, Author and Citation. Although there will be overlap in the results you get, each method will find unique items that the other two searches couldn't. The duplicates you retrieve can easily be eliminated by whatever Citation Management software you are using so don't stress about seeing many of the same articles in your results. It's the unique items being retrieved that will make your search thorough.
Would you like to see the literature research process used in real-life problem solving?
Kirkwood, Patricia Elaine and Parker-Gibson, Necia. Informing Chemical Engineering Decisions with Data, Research, and Government Resources. Morgan & Claypool, 2013. Synthesis Lectures on Chemical Engineering and Biochemical Engineering #1.
Chapter 7: Case Study 1: Finding a More Ecologically Friendly Plastic for Product
Chapter 8: Case Study 2: Biofuels: Using (Mainly) Governmental Resources to Inform Your Decisions
The case studies are in the chemical and agricultural engineering fields but the basic concepts and techniques used could apply to all areas of engineering. Kirkwood and Parker-Gibson do not use the PICO formula per se but you can easily see those concepts in their research questions. Take note of how in both cases background material applicable to the research question was gathered first before searching literature databases for articles, etc. You'll also see how decisions were made on which terms to use in the search statements and how the search was refined as information was found.
Also note, that when doing a literature review for problem solving, there maybe more than one PICO question or more than one informational need to the problem. This contrasts with academic research in which you may be investigating a single question or aspect of a topic.