Need help figuring out changing codes - P0455 to P0172/P0175

[slowride]

As my luck works, I have to get my 06 Tahoe 5.3 L59 inspected this month and I started getting the "tighten fuel cap" message and my check engine light came on with P0455 code for an evap leak. So from what I read, I ordered a new gas cap which showed up yesterday. I put it on and cleared the code and when I was on the road the engine light came back on with P0172/PO175 rich condition codes, but no P0455 code. Today just to see what would happen, I put the old gas cap back on and cleared the codes then went for a drive and light came back on with the P0455 code but no P0172/P0175 codes. Does this indicate something to look at that Im missing? I dont know which direction to go with the 2 different code indications when I switch parts. I also installed a new evap solenoid, the one on the front of the intake, but that made no difference either way with the new one or the old one when switching gas caps.

 

[PNWYukon]

Conditions for Setting the DTC

The EVAP system is not able to achieve or maintain a calibrated level of vacuum within a set amount of time.

Diagnostic Aids

• A fuel fill cap that is left OFF after a fuel fill will cause this DTC to set.
• A loose, missing, or damaged fuel fill cap can cause this DTC to set.
• A blockage or restriction in the EVAP purge solenoid, purge pipe EVAP canister, or vapor pipe, can cause this DTC to set.
• A temporary blockage in the EVAP purge solenoid, purge pipe, or EVAP canister could cause an intermittent condition. Inspect and repair any restriction in the EVAP system.
• To help locate intermittent leaks, use the J 41413-200 to introduce smoke into the EVAP system. Move all EVAP components while observing smoke with the J 41413-SPT.
• To improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles with the J 41413-SPT.
• Observe the Freeze Frame/Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition occurs that caused the DTC to set. This may assist in diagnosing the condition.

Special Tools Required

• J 41413-SPT High Intensity White Light
• J 41413-200 Evaporative Emissions System Tester (EEST)
• J 41413-300 EVAP Cap and Plug Kit
• J 41413-311 EVAP Plug
• GE-41415-50 Fuel Tank Cap Adapter

Circuit/System Testing

Important:

• Larger volume fuel tanks and/or those with lower fuel levels may require several minutes for the floating indicator to stabilize.
• Refer to the J 41413-200 operation manual for detailed instructions.

1. Connect the J 41413-200 to the vehicle service port.
2. Seal the EVAP system and use the flow meter on the J 41413-200 , calibrated to 0.51 mm (0.02 in) to determine that there is no leak in the EVAP system.

• If a leak is detected, use the J 41413-200 to apply smoke to the EVAP system at the service port until the leak is located.

1. To test for a restriction, connect the J 41413-200 nitrogen/smoke hose to the J 41413-311 brass cone adapter. Disconnect the hose at the fuel cap end of the GE-41415-50 . Connect the J 41413-311 to the disconnected hose on the GE-41415-50 . Install the GE-41415-50 filler neck end only to the vehicle.
2. Allow the engine to idle.
3. Use the Purge/Seal function to seal the system with a scan tool.
4. Command the EVAP canister purge solenoid valve to 30 percent.
5. The vacuum/pressure gauge on the J 41413-200 and the FTP parameter on the scan tool should both show vacuum.

• If the vacuum/pressure gauge shows vacuum, but the FTP parameter does not show vacuum, replace the FTP sensor.
• If neither the FTP parameter nor the vacuum/pressure gauge shows vacuum, repair the restriction in the purge path. Refer to Evaporative Emissions Hose Routing Diagram.

1. Verify that the vacuum increases to the abort limit on the scan tool or more than 3.2 volts, and the value is closely similar between the scan tool and the vacuum/pressure gauge on the J 41413-200 .

• If the values are not similar or the voltage did not reach 3.2 volts, replace the FTP sensor.

 

[slowride]

I think I found the problem. Was clearing out the codes again today with a different scanner and I looked at the fuel alcohol % and wow. Looks like somebody filled my tank with 150 proof lol. I posted about the same issue I had on this same truck last year when I was trying to get it inspected. It was showing p0172/0175 codes then too. I had fuel trims reset and alcohol content zeroed out which fixed it then but looks like it came back right on time. I have been running non ethanol gas from the same 2 places since I got it reset last year. Not sure whats going on to cause such a high alcohol content to show.
Added- Just went and put 8 gallons of gas in at 2 different stops which is supposed to trigger a fuel alcohol content relearn but status says inactive each time I put gas in and drove around so its staying at 74% alcohol reading

 

[ks03]

mudsport has the same thing going on it sounds like

https://www.tahoeyukonforum.com/threads/operating-system-update-for-e85-compatibility-tsb.125622/

 

[Fless]

If you're certain about the fuel composition being incorrect, reset it with the scan tool. Once the percentage is reset, the PCM will revert to the non-E85 table. And if the percentage is wonky, you may need a calibration update, or diagnosis or replacement of the fuel composition sensor.

 

[ks03]

Does it actually have a fuel composition sensor, or just virtual?

 

[Fless]

2006 should have the sensor. It's around the fuel filter on the driver's side frame rail. Not inexpensive...

 

[slowride]

From what I read online trying to figure this out, 2006 and up have the virtual sensor. There is no frame mounted fuel filter on the 2 '06 Tahoes I have, I checked. I dont know why the fuel composition learn mode wont kick in after refueling. I emailed Chevy customer service about that VFFS update software to see if it had been done already on this truck and they told me to contact local dealer. I called local dealer service dept yesterday and told them I wanted to see if they could check as well. The lady I spoke to was very nice and seemed like she was trying to help by putting in my VIN but all she could tell me was that it hadnt been done at that dealership. So I would have to bring it in and have it done which they couldnt give me a cost on. If the update has been done, it didnt work so I dont want to have to pay for it if its not going to work. The shop I went to last year to get this done ended up closing so I guess I will be riding around trying to find somebody with the right scan tool who understands what needs to be reset. I cant shell out $500 or more for one so if anybody has a suggestion for a low price scan tool that will reset the fuel composition and fuel trims or even a programmer to eliminate the flex fuel option if that is even possible, please let me know. Thanks

 

[exp500]

Many of us here use one or the other to help in times like you are having,
Vetronix GM Tech2 with Case for GM/SAAB/OPEL/SUZUKI/ISUZU with Candi Module Tech2
Vxdiag VCX Nano for GM/Opel Diagnostic/ECU Programming Tool
Pays for itself quickly, as you have noticed the diagnostic / reprogram cost.

 

[Fless]

From what I read online trying to figure this out, 2006 and up have the virtual sensor. There is no frame mounted fuel filter on the 2 '06 Tahoes I have, I checked. I dont know why the fuel composition learn mode wont kick in after refueling. I emailed Chevy customer service about that VFFS update software to see if it had been done already on this truck and they told me to contact local dealer. I called local dealer service dept yesterday and told them I wanted to see if they could check as well. The lady I spoke to was very nice and seemed like she was trying to help by putting in my VIN but all she could tell me was that it hadnt been done at that dealership. So I would have to bring it in and have it done which they couldnt give me a cost on. If the update has been done, it didnt work so I dont want to have to pay for it if its not going to work. The shop I went to last year to get this done ended up closing so I guess I will be riding around trying to find somebody with the right scan tool who understands what needs to be reset. I cant shell out $500 or more for one so if anybody has a suggestion for a low price scan tool that will reset the fuel composition and fuel trims or even a programmer to eliminate the flex fuel option if that is even possible, please let me know. Thanks

If you let us know around where you live, perhaps someone with a Tech 2 nearby would stop by and see what calibration is on it now. And it's free to update with TIS2000. And a Tech 2 would be able to reset the fuel composition on an '06.