Can’t pass evap

Andre Diagnostician District of Columbia Posted   Latest  
Unsolved
Emissions
2007 Cadillac CTS 3.6L (7 LY7) 5-spd (5L40-E)
P0455 — EVAP System Leak Detected (large leak),
Will Not Pass Evap Test

This vehicle came to me with a p0455 evap system large leak and I found the purge valve bleeding down would not seal replaced purge valve and tested system as individual parts purge seals and cycles properly disconnected purge and test the rest of the system vent valve and tank pressure sensor bot working properly. Attempted to do service bay evap test and it would not run but as everything has passed testing I sent it down the road. Now it’s back same code and will not pass evap bay test . Drove vehicle to run evap monitors test ran and failed. Recheck all parts and find no faults any help would be appreciated 

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Darren Technician
Wisconsin
Darren
 

Fuel tank pressure sensor…?

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Nick Service Manager
Indiana
Nick
 

On GM vehicles I use the Evap purge/seal test rather than the service bay test. Increase the purge solenoid duty cycle until the fuel tank pressure sensor reads about 10 inhg, then seal the system. Watch the fuel tank pressure closely, a large leak should show a pretty quick increase in tank pressure. Fuel tank pressure should show right around 0 inhg with the engine off and fuel cap removed

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Andre Diagnostician
District of Columbia
Andre
 

My scan tool will test purge or vent key on engine off or service bay test key on engine running

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Rusty Owner/Technician
Massachusetts
Rusty
 

Seal the system (close the vent valve) and tightness-test or pressure test the system with a smoke machine. A “purge/seal“ test will confirm a leak or verify a fix

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Andre Diagnostician
District of Columbia
Andre
 

Smoke tested system with smoke machine and flow sensor the ball drops all the way to the bottom when vent is closed bellows smoke vent open smoke stops and ball drops when the vent is closed

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Rusty Owner/Technician
Massachusetts
Rusty
 

As others have urged, run a “purge/seal” with your scan tool. I suspect the vacuum will fall away quickly. If possible, clamp off the rubber hose between the filler neck and the tank and try again. If your vacuum hold, you have a filler neck leak. I have had a seal around a GM sending unit leak under vacuum but not under pressure. I had to drop the tank, use a vacuum pump, and listen with a…

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Glenn Owner/Technician
Texas
Glenn
   

Hello Andre, Now you have to ask yourself why it would not pass the bay test the first time it was there. Go through the flow chart for code P0455 and follow it all the way through to the end. Have you tested the fuel cap a couple of times and made sure it would pass? I also agree with Darren concerning the FTP sensor. The Ethanol in modern fuel degrades the sensors. Is it possible the…

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David Diagnostician
Georgia
David
 

Does fuel level indicate properly?

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Andre Diagnostician
District of Columbia
Andre
 

Yes

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Andrew Diagnostician
Arizona
Andrew
 

I'm confused it sounded like you said the fuel tank pressure sensor not working properly. Large leak diag is pretty easy usually, go into bidirectional controls on your scan tool while monitoring fuel tank pressure sensor, with fill cap removed tank pressure sensor should read baro. Reinstall fill cap, close vent valve (with scan tool) and open purge, tank pressure should drop and keep…

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Joel Diagnostician
California
Joel
 

First step: with key on engine off and fuel cap off , what is the voltage reported by the FTP?

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Andre Diagnostician
District of Columbia
Andre
 

Key on engine off FTP voltage is spot on 1.4 volts close vent voltage goes down to about.22-.26 volts and holds

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Paul Mechanic
Illinois
Paul
 

So you can close vent solenoid with engine running?

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Paul Mechanic
Illinois
Paul
 

As others have stated, use the purge and seal to get a feeling of system integrity. Usually a 455 setting indicates the system can't reach it's target negative pressure. P0455 are usually the easiest to locate/diagnose out of all leaks. Just remember, just because you hear vent cycling doesn't mean it's sealing and using pressure to test system integrity can be misleading as your maybe enhancing…

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Tony Owner/Technician
Missouri
Tony
 

And to add, if pressure testing from anywhere but the cap, such as at the test fitting near the purge valve, pressure/smoke won't escape the filler pipe on GMs due to a check valve built into the bottom of the filler neck, so the integrity of the neck and cap seal are not tested in this scenario.

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Interesting
Andre Diagnostician
District of Columbia
Andre
 

With the cap loose the smoke will appear around the cap it takes more than 3 psi to lift the rollover valve for that to happen

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Tony Owner/Technician
Missouri
Tony
 

I wouldn't pump 3 psi into a fuel system.

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Andre Diagnostician
District of Columbia
Andre
 

I didn’t my smoke machine is regulated to 1psi thanks for your response

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Tony Owner/Technician
Missouri
Tony
 

Then I assume you meant removing the neck from the tank hose and testing it separately, but I don't see where you detailed that step.

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Andre Diagnostician
District of Columbia
Andre
 

The filler neck can be tested with the rest of the system no need to remove and test separately . please don’t tell me you are working that hard

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Tony Owner/Technician
Missouri
Tony
 

OK, you got this, keep on being a dick.

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Geoff Diagnostician
Hawaii
Geoff
 

Your words: "With the cap loose the smoke will appear around the cap it takes more than 3 psi to lift the rollover valve for that to happen"

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Glenn Owner/Technician
Texas
Glenn
 

Hello Andre, Do you have All Data? It has specific steps that need to be followed in order. Specifically follow the conditions for running and clearing the MIL/DTC information. All this skipping around “rabbit hunting” will get you nothing but frustration and confusion.

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Andre Diagnostician
District of Columbia
Andre
 

No i do not have all data but I do have Mitchell and have tested the entire system cap for a leak with cap tester (stant) original purge valve replaced would not seal properly. Replacement valve checked and passed blocks and seals consistently smoke tested rest of system smoke flow’s from vent until closed once vent is closed smoke stops flow meter ball starts to fall and goes all way to…

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Paul Mechanic
Illinois
Paul
 

1 psi limit- you run the risk of creating a leak with any more and again, the vehicle uses negative pressure to test so you are likely masking issue. At this point, check the price on a cap and vent solenoid. You'll always want a know good cap around anyway for quick checks on these EVAP leaks. Vent solenoid s aren't that bad either usually on GMs. Just getting to them on some models. I have…

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Andre Diagnostician
District of Columbia
Andre
   

I am very aware of the pressure limits on evap systems at 1 psi I was resp to someone who thought the filler neck would not be pressurized due to the check valve in the bottom of filler ( rollover valve ) I posted this question because during testing I can check all the items individually and they all pass . The vehicle should be able to run a service bay test which tests the entire system purge…

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Paul Mechanic
Illinois
Paul
   

I'm not sure if you listed that vent solenoid was replaced, I saw purge was and cap was tested(I hope you vacuum) . Are you still chasing the P0455 or is it not running EVAP test/monitor? Large leak should be revealed with smoke. Where are you introducing smoke at? Had a late model Malibu setting a p0456 and was testing at purge valve connector connects to rest of system as there was no test…

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Timothy Owner/Technician
Wisconsin
Timothy
 

You're still not checking the vehicle the way the PCM checks it: use the Purge/Seal option on the scan tool. It will check the system under vacuum, just the way the ECM checks it. Regardless of the smoke testing, the system obviously still has a leak. Pressure testing with a smoker sometimes will close leaks, as several others have stated. The scanner testing will show you whether it still has…

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Andre Diagnostician
District of Columbia
Andre
 

Thanks for the reply my scanner does not show a purge and seal test but does have an evap service bay test that will run the test on demand as long as coolant temperature is not too high . The test starts and I can see the purge operation on the tool but it says waiting and the vent doesn’t show that it closes or the pressure sensor voltage doesn’t change after 20 minutes the test times out with…

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Paul Mechanic
Illinois
Paul
 

If you can command purge or vent and monitor fuel pressure sensor PID, make your own test: clamp off at vent and command purge til you hit about 10"hg, then kill purging and watch rate of decay. Then you can flip it and command vent closed and control purge by grounding at purge valve until you got same target vacuum. Then you can decided which side of system may be at fault. Curious at to what…

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Timothy Owner/Technician
Wisconsin
Timothy
 

Must be a truly weird scan tool to not have that function. The test goes back decades on GM vehicles! I am totally surprised that it is not available. The in bay service test can be hit-or-miss as to whether it works. It must be performed under the exact same conditions as the normal Evap test the PCM runs for the monitor. Temperature has to be within eight degrees or less between IAT and ECT…

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Andre Diagnostician
District of Columbia
Andre
 

It may not be on this test on other vehicles but it’s not listed on this one suspect ECM problem as sealed vent hose and opened purge to pull into a vacuum and sensor voltage went up and vacuum held gonna condem ECM

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Geoff Diagnostician
Hawaii
Geoff
 

Did you check if Mode$06 test results will show you "how" the diagnostic is failing?

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