Uploaded May 2026 | Updated September 2026, 3 weeks ago
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 on a 2008 GMC Envoy 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.
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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
scannerdanner.com/join-scannerdanner-premium.html
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
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 on a 2008 GMC Envoy 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
scannerdanner.com/join-scannerdanner-premium.html
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
![Chevy Corvette Cold Engine Misfire [Part 2]](https://i.ytimg.com/vi/lnG4Jl92TEw/mqdefault.jpg "Chevy Corvette Cold Engine Misfire [Part 2]
00:00 - review of fuel trim vs misfiring
00:48 - review of RPM drop test and driver shut-down
03:37 - review of spark plug color/cooling system
04:40 - review of secondary ignition waveforms
07:23 - lean misfire that I missed!
08:03 - internal vacuum leak (V-type engine)
10:20 - concerns of contaminated fuel/sticking injectors
11:07 - clip of unsticking an injector
11:55 - smoke test on the intake (vacuum leak test)
13:33 - picoscope secondary waveforms
16:47 - Snap-on vs Pico (zoom differences)
17:08 - SDP Scope and Scan Tool Classes https://www.scannerdanner.com/scannerdanner-premium-chapters/scope-and-scan-tool-classes.html
21:22 - setting a scope trigger
22:15 - flex-fuel Jeep review
https://youtu.be/glYGv3CyVWU (part 1)
https://youtu.be/Hjgs_8wX6Ks (part 2)
https://youtu.be/7kgnwJX40C4 (part 3)
23:50 - suspected sticking injectors (lean misfire waveforms)
25:04 - #2 cylinder lean misfire
25:37 - whats the fix?
28:25 - SD Premium!
https://www.scannerdanner.com/scannerdanner-premium-chapters.html
ScannerDanner Tools:
https://www.scannerdanner.com/tools.html
https://www.amazon.com/shop/scannerdanner
For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium https://www.scannerdanner.com/join-scannerdanner-premium.html There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!
Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.")
![85 Celica 22RE - Intermittent Low Power Condition [Part 2]](https://i.ytimg.com/vi/omqPoEgfiQc/mqdefault.jpg "85 Celica 22RE - Intermittent Low Power Condition [Part 2]
Toyota 22RE Engine - fuel pump diagnostics - low pressure and bleed down problems are addressed in this video
00:00 - review of part 1
1:10 - removing the fuel tank with my son
8:26 - what ruined the old fuel pump
10:40 - cleaning the fuel tank
13:55 - what the tank looks like after cleaning
14:26 - installing the new fuel pump/reinstalling fuel tank
16:30 - tips on purging the fuel lines
18:12 - am I thinner or is it the shirt? lol
21:14 - fuel pressure measurements (new pump)
22:53 - using the VAF to energize the fuel pump
23:13 - fuel pressure bleed down issue
24:00 - engine running fuel psi tests
24:42 - engine noise testing
25:20 - fuel pump current (new pump)
https://www.aeswave.com/scannerdanner-c512/
28:20 - fuel psi bleed-down testing
📘 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
🔧 Looking for Deeper Training?
Whether youre a DIYer, an aspiring tech, or a professional looking to sharpen your skills, join ScannerDanner Premium for next-level diagnostics training:
👉 Join Here – 14 Days for $1
https://www.scannerdanner.com/join-scannerdanner-premium.html
On ScannerDanner Premium, youll get:
*In-depth classroom lectures straight from my book
*Exclusive case studies with live vehicles pulled into class
*Real-time troubleshooting using proven methods
*Post help requests on our forum
*Fundamental training on diagnosing automotive electrical and electronics systems.
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.")
![Shorted Ignition Coil Primary Winding [DONT LET THIS FOOL YOU!]](https://i.ytimg.com/vi/p68w9CJG00g/mqdefault.jpg "Shorted Ignition Coil Primary Winding [DONT LET THIS FOOL YOU!]
Shorted Ignition Coil Primary Winding [DONT LET THIS FOOL YOU!]")
