Teaching My Son Why “New” Parts Mean NOTHING | EVAP Diagnosis

Beau is back in the shop with me, and this one turned into a perfect training moment for every rookie tech out there. What started as a simple GM EVAP large leak code turned into a great lesson on why you can’t stop after a smoke test. The system passed the leak test, but the purge valve still had to be checked. We commanded the purge valve with the scan tool, verified current flow with an inductive amp probe, looked at voltage and current together, and proved the computer was controlling the valve. The problem? The purge valve was mechanically stuck closed. This is one of those cases where the electrical side of the circuit looked good, but the mechanical side of the solenoid failed. That is a huge lesson for Beau and for every new technician learning diagnostics: just because a circuit is being commanded doesn’t mean the component is actually doing its job. We also ran into another important lesson after replacing the valve — the aftermarket purge valve did not respond correctly at low duty-cycle commands. The genuine GM valve worked properly, confirming why part quality can absolutely matter in diagnostics. This video is not just about an EVAP code. It’s about teaching a rookie how to think, how to test, and how to prove a fault before replacing parts. 🔧 Looking for Deeper Training? Whether you're a DIYer, an aspiring tech, or a working technician, ScannerDanner Premium gives you in-depth diagnostic training built around real testing and real troubleshooting: 👉 Join Here – 14 Days for $1 https://www.scannerdanner.com/join-sc... On ScannerDanner Premium, you'll get: *In-depth classroom lectures based on the material in my book *Case studies with real vehicles brought into class *Troubleshooting using proven diagnostic methods *Access to our private forum *Fundamental training in automotive electrical, electronics, and drivability diagnostics 📘 Want to Learn More About Diagnostics? Check out my field manual, Engine Performance Diagnostics, available as both an eBook and paperback at: 👉 https://linktr.ee/scannerdanner ScannerDanner Tools: https://linktr.ee/scannerdanner ⚠️ Disclaimer: ScannerDanner LLC is not responsible for misuse, unauthorized changes, or incorrect application of any information provided. Always follow proper safety protocols when using tools, equipment, or procedures discussed in this video. Use this content at your own risk. 0:00 Intro 0:25 Smoke Test Passes, But Purge Still Needs Checked 1:27 Commanding the Purge Valve — No Vacuum 3:48 Electrical Testing the Purge Circuit 6:16 Current Flow Confirms the Valve Is Being Controlled 8:29 How a Stuck Closed Purge Sets a Large Leak Code 10:22 Voltage, Current, and Ground-Side Switching Explained 12:25 Confirming a Mechanically Stuck Purge Valve 15:30 New Purge Valve Installed 16:14 Aftermarket Valve Doesn’t Act Right 20:19 Genuine GM Purge Valve Test 21:02 Final Confirmation / Wrap-Up