CEL came on yesterday, 2006 ODB trouble codes

[2006Tahoe2WD]

Got a new GM vent valve from the dealer and installed.
I did another purge/seal test and got the same results.
I had an idea. What if the Foxwell was sending some amount of "open" signal to the purge valve even when commanded to seal. Here is what I did.
After some amount of the purge/seal test (vent valve not venting) I hit seal and then went to the purge valve and unplugged it. Guess what holds vacuum like crazy.
The only thing I can guess is the Foxwell is sending some amount of open command to the purge valve. I'll send them an email and ask.
Right now all the drive cycles are "OK" except the evap. I drove around for about an hour.
The evap may have a ways to go or is somehow still unhappy.

 

[Fless]

The evap doesn't run on a warm engine. It'll run from a cold start, but other conditions need to be met, like fuel level between 1/8 and 7/8 full (because of fuel vapor expansion), outside temp needs to be within a certain range, and the coolant temp needs to be within around 11° (I'm not exactly sure of this value, but it's close) of outside air temp, and a few other conditions. Run it for a few days and see what happens.

 

[2006Tahoe2WD]

Okay, thanks. I'll run for a bit and see. I don't have an easy way to get a scope on the signal going to the purge valve but I may try to listen with a stethoscope. It would be good to confirm a bug in the Foxwell 510 software.

 

[2006Tahoe2WD]

I filled the tank so I need to get it down to 7/8 or 3/4. Should take no longer than a week.

 

[2006Tahoe2WD]

I went to RockAuto and ordered the OEM purge valve 12581282. I'll put that in and then be good with both valves new and OEM.

 

[2006Tahoe2WD]

The drive cycle for the evap. system hasn't completed yet so I guess I need more cold starts and get the gas tank down a bit. Stay tuned.

For what it is worth - I got my stethoscope out and listened to the purge valve during the evap/seal test when it should have been closed. It was rattling so it was open some amount. I sent another email to Foxwell asking if they have updated software to fix the issue. I tried a number of different things with the Foxwell e.g. going into the vent valve and closing that and then going to the purge valve and closing that. Didn't work - when you get out of the vent valve control it opens the vent valve. So that bit of mystery (vacuum increases during the "seal" part of the test) remains.

 

[Fless]

The drive cycle for the evap. system hasn't completed yet so I guess I need more cold starts and get the gas tank down a bit. Stay tuned.

For what it is worth - I got my stethoscope out and listened to the purge valve during the evap/seal test when it should have been closed. It was rattling so it was open some amount. I sent another email to Foxwell asking if they have updated software to fix the issue. I tried a number of different things with the Foxwell e.g. going into the vent valve and closing that and then going to the purge valve and closing that. Didn't work - when you get out of the vent valve control it opens the vent valve. So that bit of mystery (vacuum increases during the "seal" part of the test) remains.

Appreciate the update. Keep 'em coming!

 

[2006Tahoe2WD]

In the mean time... at the risk of derailing my own thread...I'm now thinking of getting a better scanner as discussed a bit above. Is there a dedicated thread on this? The Autel units can get expensive but they have a MaxiCom MK808BT Pro that isn't too much.

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[2006Tahoe2WD]

Well, I did the cold start and idle with big electrical load for 3 minutes and then did a couple of periods at 55 ish MPH and coasting to ? 30MPH. Not easy to do this on the freeway around here. The status still shows EVAP INC - all the other I/M status lines are OK or NA.
I did find one of the O2 resister values was not in spec. This should be resolved with the 4 new O2 sensors showing up soon. Also, I didn't see all the transmission codes again. Could it be that the transmission shop guy was correct? The trans codes would be fixed with a new ignition switch - so far so good on that. Knocking on wood as I type. I still have other codes showing up. Fuel pressure sensor and fuel level sensor and stop light switch. I want to get the EVAP nailed down and then move shift concentration to the other codes that keep coming back. I'm not liking the idea of pulling the gas tank - I'll probably have the shop do that if needed. Continue staying tuned. The P code journey continues.

 

[Fless]

A fuel TANK (?) pressure sensor code (what was the code?) is likely related to the evap test results, or vice versa. Could be the cause, although you did measure the fuel tank pressure changing during the purge and seal, IIRC.

I don't think your truck has a fuel pressure sensor.

 

[2006Tahoe2WD]

A fuel TANK (?) pressure sensor code (what was the code?) is likely related to the evap test results, or vice versa. Could be the cause, although you did measure the fuel tank pressure changing during the purge and seal, IIRC.

I don't think your truck has a fuel pressure sensor.

Maybe it should be called tank vapor pressure. Code P0451, P0454.

 

[2006Tahoe2WD]

It gets inserted in the top part of the fuel pump assembly.

 

[2006Tahoe2WD]

As I understand.... The three devices (purge, vent, pressure sensor) work together to get the gas fumes burned up and to tell if that system is working without any "holes". I imagine the pressure sensor could go bad and the ECU thinks there is a leak when there isn't.

 

[2006Tahoe2WD]

Minor update. I looked at the active tests available on the Foxwell 510 and there is a vent valve "test". You can turn the vent valve on and off manually. The good thing is the gas tank pressure sensor readings along with the purge valve command are also listed. So I tried this test for the 5th+ time and when I close the vent valve the pressure starts going to more vacuum. This means the purge valve is not closing all the way. The new purge valve should be here in a day or so. Side note: the reading from the tank pressure valve seem to be smooth and what might be expected. Hopefully the tank pressure sensor is okay. Big project to change that out. Probably need to drop the tank a bit. There are Silverado videos where they raise the bed instead of dropping the tank - I can't do that (Tahoe).

 

[Fless]

The tanks are not that difficult to drop slightly to get to the fuel tank pressure sensor, but are a bit more involved to fully drop. Not an impossible task although, when fully dropping, the lines you disconnect can vary between the flex fuel and the gasoline-only tank styles. I'm not sure how much difference there is between my '04 Flex Fuel and your 2006, though. Pulling the driveshaft can help with that access.

Easy enough to drop somewhat for access to reach the top of the fuel pump, especially if the tank is nearly empty. Cross that bridge when you come to it.

 

[2006Tahoe2WD]

The tanks are not that difficult to drop slightly to get to the fuel tank pressure sensor, but are a bit more involved to fully drop. Not an impossible task although, when fully dropping, the lines you disconnect can vary between the flex fuel and the gasoline-only tank styles. I'm not sure how much difference there is between my '04 Flex Fuel and your 2006, though. Pulling the driveshaft can help with that access.

Easy enough to drop somewhat for access to reach the top of the fuel pump, especially if the tank is nearly empty. Cross that bridge when you come to it.

Sure, as you say hopefully not too bad to drop just enough for the pressure sensor. There was a video where a guy did that. Didn't look too fun. How about cutting a hole in the floor?

 

[2006Tahoe2WD]

Here is a video of a pressure sensor change without dropping the tank all the way.

 

[Fless]

How about cutting a hole in the floor?

I have a feeling that you're not that kind of guy.

I found on mine that if I pull the driveshaft I can get my head up in the driveshaft tunnel, and be able to see what I'm doing on the top of the tank. Just disconnect the rear u-joint and let the end down, or remove it completely. If you remove it you might want to have a small pan near the end of the transmission to catch any fluid that might come out.

 

[OR VietVet]

If you cut a hole in the floor.................I have no words! Butcher job! I guess I did have words!

 

[Fless]

Just so you know what it looks like under there without the tank, here's a pic. That way you won't have to drop yours all the way to see!