Fuel tank pressure sensor PID

[John Williams]

Hello, I have the OBDLink MX+ scan tool that I use with both "OBD Link" and "Car Scanner' apps with my 2008 Pontiac Grand Prix. My issue is that I cannot read the Fuel tank pressure sensor data with the OBDLink however I can read this Pid with the Car Scanner app which is named " Evap system vapor pressure" but I believe it is the same data reading as the Fuel tank pressure sensor Pid in OBD Link. Seeing that I know the data is available with Car Scanner would anyone be willing to give me some advice on what I would need to do to make this work with OBDLink, if it is even possible.

Thanks in advance for any help given.

 

[TJBaker57]

Hello, I have the OBDLink MX+ scan tool that I use with both "OBD Link" and "Car Scanner' apps with my 2008 Pontiac Grand Prix. My issue is that I cannot read the Fuel tank pressure sensor data with the OBDLink however I can read this Pid with the Car Scanner app which is named " Evap system vapor pressure" but I believe it is the same data reading as the Fuel tank pressure sensor Pid in OBD Link. Seeing that I know the data is available with Car Scanner would anyone be willing to give me some advice on what I would need to do to make this work with OBDLink, if it is even possible.

Thanks in advance for any help given.

A quick question.

Does the parameter show up in the list of available parameters in the OBD Link app? Or is it not even there?

 

[John Williams]

Hello, and thank you for your reply.
If I understand your question correctly, the answer is no. OBDLink lists the pid as fuel tank pressure sensor whereas Car Scanner lists it as Evap system vapor pressure.
I've attached two screenshots of the OBDLink app PID parameters if that helps.
Thanks again.

 

[TJBaker57]

Hello, and thank you for your reply.
If I understand your question correctly, the answer is no. OBDLink lists the pid as fuel tank pressure sensor whereas Car Scanner lists it as Evap system vapor pressure.
I've attached two screenshots of the OBDLink app PID parameters if that helps.
Thanks again.

Well I can poke around a bit but seeing that it is CANBUS somewhat leaves me out in the cold as I have no real experience with that.

I have noticed that "F432" PID in the past but nothing I have supports that PID.

Our older vehicles (pre CANBUS) used PID 114E for fuel tank pressure and that returns a single byte, not 2 bytes as your screenshot indicates.

In Car Scanner, If you look in "Sensors" in the "Settings" menu and find the PID that works for you in that listing... What is the PIDs "ID" number listed there ??

 

[John Williams]

Thanks again for your assistance with this . As I'm sure you can tell I'm not well versed in the OBD2 world so I appreciate your patience.

As far as I can tell the Pid # In "Car Scanner" is listed as " ID66 Evap System vapor pressure" I was thinking there would be more information on each PID as in the OBDLink but unless I'm doing something wrong this is all the info I get with Car scanner.
I've attached a screenshot if that helps!

Thanks again.

 

[TJBaker57]

As far as I can tell the Pid # In "Car Scanner" is listed as " ID66 Evap System vapor pressure" I was thinking there would be more information on each PID as in the OBDLink

I asked for the ID number so that I would be looking at the same PID/sensor you are. That ID number is specific to Car Scanner and has no significance outside of that app.

Having that ID## I can maybe see what Car Scanner does behind the scenes for that sensor.

I cannot run OBDLink here as I don't use any of their OBD devices but there is another app "OBD Fusion" that is very similar, maybe even from the same company. I do have the OBD Fusion app.

 

[John Williams]

Okay, just wanted to say thanks so much for the help on this but it's not worth wasting any more of your time on it.
When I have EVAP issues again with this car I will just resort back to using the Car Scanner app.
Again, thank you so much for all the help!!

 

[TJBaker57]

Okay, just wanted to say thanks so much for the help on this but it's not worth wasting any more of your time on it.

Well thanks, and you are welcome! This has actually been on my radar for quite a while and high time I get into it.

I may have a partial answer for you. Try this when you get a chance..... it works for a 2008 4.2 TrailBlazer ECM.

Can you edit the values in the screenshot(s) you posted from the OBDLink app?

If yes then change the "OBD Mode" from "22" to "01".
Change the PID number from "F43201" to just "32".

See if that yields anything.

You may see some weird values as the equation is wrong but I am working on that. I know what it needs to be, just have to verify it. Should look something like "signed(A+B)/4" I believe. EDIT: The equation would return the pressure in pascals.

 

[John Williams]

Success!! Wow you're incredibly.
I modified the PID as you instructed and got a response from the ECU.
I left the equation as it was and the data returned a value of 1.9 PSI If it helps. Using the Car Scanner app which I believe is accurate, and the fuel tank vented to atmosphere, I get a value of -14 Pascal.
Also attached a screenshot of the output.

 

[AmpOverload]

I don't know where (Mode $22) PID $F432 (with or without a trailing "01") comes from. FWIW, the only place I've ever seen that PID is on certain Ford vehicles, never on a GM vehicle (so far, anyway! ).

I fired up Tech2Win, selected a 2008 Pontiac Grand Prix (assuming 'W' body, 3.8L V6 "L26" engine, and "Without Air Pump"), then monitored what PIDs it was requesting on the "EVAP Data" page (which includes 2 "Fuel Tank Pressure Sensor" entries, 1 in mmHg and the other in volts -- which is very typical for GM vehicles of this era) and didn't see that PID there either.

The PID list included:

1. Mode $22 PID $114E is "Fuel Tank Pressure" in volts, using the formula "A/256*5".
2. Mode $22 PID $1297 is "Fuel Tank Pressure" in native units of "inches H2O", using the formula "signed(A*256+B)/1024".

The list did not include PID $0032 ("Evap System Vapor Pressure"). Nevertheless, if the vehicle is capable of reporting it, the equation (per SAE J1979) is "signed(A*256+B)/4", in Pascals.

To no surprise on my part, the list also did not include PID $F432.

I modified the PID as you instructed and got a response from the ECU.
I left the equation as it was and the data returned a value of 1.9 PSI If it helps. Using the Car Scanner app which I believe is accurate, and the fuel tank vented to atmosphere, I get a value of -14 Pascal.

That value of 1.9 PSI sounds wrong. The FTP (Fuel Tank Pressure) on a 2004 Century ranges from about 0.0 to about 0.376 PSI (10.4 inches H2O) during EVAP system testing.

Hope that helps a bit. Don't hesitate to ask for any clarification or additional info, though.

P.S. @TJBaker57: IIRC, "OBD Fusion" (EDIT: formerly known as "TouchScan") was (and may still be) the same software as "OBDLink", just not restricted to ScanTool.Net hardware (e.g. OBDLink MX, etc).

 

[TJBaker57]

left the equation as it was and the data returned a value of 1.9 PSI If it helps.

That value of 1.9 PSI sounds wrong.

As I had mentioned the existing equation is clearly wrong. The equation needs to resolve a signed hexadecimal value for dealing with negatives and that equation does not.

The OBD Fusion equation syntax gave me a workout but I prevailed.

For tank/evap pressure in Pascals:
int16(combine(A,B))/4

For tank/evap pressure in mm/Hg:
int16(combine(A,B))/4 * 0.00750062

For tank/evap pressure in in/H2O:
int16(combine(A,B))/4 * 0.00401865

For tank/evap pressure in PSI:
int16(combine(A,B))/4 * 0.000145038

 

[AmpOverload]

For tank/evap pressure in Pascals:
int16(combine(A,B))/4

For tank/evap pressure in mm/Hg:
int16(combine(A,B))/4 * 0.00750062

For tank/evap pressure in in/H2O:
int16(combine(A,B))/4 * 0.00401865

For tank/evap pressure in PSI:
int16(combine(A,B))/4 * 0.000145038

I think it would be interesting now to compare the values reported by Mode $01/$22 PID $0032 to the value reported by Mode $22 PID $1297 ("Fuel Tank Pressure") for the 2008 Grand Prix.

One nice thing I see as I work on newer vehicles is more support of the low-numbered Mode $01/$22 PIDs. In fact, I have occasional access to 2 qualifying vehicles, one GM and one Ford, that support PID $0032, so I plan to test this to satisfy my curiosity.

 

[TJBaker57]

I think it would be interesting now to compare the values reported by Mode $01/$22 PID $0032 to the value reported by Mode $22 PID $1297 ("Fuel Tank Pressure") for the 2008 Grand Prix.

One nice thing I see as I work on newer vehicles is more support of the low-numbered Mode $01/$22 PIDs. In fact, I have occasional access to 2 qualifying vehicles, one GM and one Ford, that support PID $0032, so I plan to test this to satisfy my curiosity.

I did take a good look today at PID 114E of mode $22 in relation to PID $32 of mode $01.

I have only seen $1297 on a 2006 P12 PCM I have.

Knowing there is but the one sensor there in the tank I expected to find a relationship between the voltage value returned by $114E.

Using a 10 turn linear potentiometer connected in lieu of an actual sensor I can vary the return voltage to the ECM.

I found that I could slightly vary the value returned by Mode/PID $22/$32 while the voltage value returned by Mode/PID $22/$114E remained the same.

This should not have been a surprise given the difference in number of bytes reported.

So for the highest resolution it looks like Mode/PID $01/$32 is preferable where it is available.

 

[John Williams]

Thank you both for all.the effort on this. As I'm just a DIYer and can't add anything meaningful to the discussion, I am more than happy to try any tests on this vehicle if that would be of any use. To make sure I was reading the right sensor and getting the right data , I blew and also sucked lightly 3 times each into the fuel filler neck while recording with the scanner, I've attached the results if that is of any interest .

 

[AmpOverload]

As I'm just a DIYer [...]

That's how it starts. Then pretty soon you find you're a full-blown OBD2 guy like me & @TJBaker57 that, as TJ recently put it, "might need an intervention".

I did take a good look today at PID 114E of mode $22 in relation to PID $32 of mode $01.

Very interesting, thanks! Looking forward to trying some similar experiments when I can get my hands on the right vehicle(s).

In a similar vein, I have already compared the 2 Mode $22 FTP PIDs ($114E and $1297) in the past. Here's a plot from a 2004 Buick Century showing engine start and eventual EVAP test:


FTP in volts ("FTP-V") is plotted on top, in red. FTP in pressure units ("FTP") is plotted on the bottom, in green. I've left the (interactive, red, vertical) cursor enabled so that folks can see the peak FTP values (in 5 different units of pressure).

What's interesting to me, and somewhat easy to miss, is that the 2-byte PID $1297 (green) seems to be showing less resolution than the 1-byte PID $114E (red). At the peak of the 2 PIDs' values on that plot (and elsewhere), there is evident "stair-stepping" on the lower (green) line for PID $1297. It is, of course, illogical that a 2-byte PID would have lower resolution than a 1-byte PID. Therefore, it strongly suggests to me that PID $1297 is being "smoothed" by the PCM's software. We've all seen that before on other PIDs (e.g. fuel tank fill level), of course, so it's not a surprise to me, just an observation.

To make sure I was reading the right sensor and getting the right data , I blew and also sucked lightly 3 times each into the fuel filler neck while recording with the scanner, I've attached the results if that is of any interest .

Excellent test...thanks for the screenshot! Just curious, are you having issues with the EVAP system on this 2008 Grand Prix? If so, it's possible to go even further than just monitoring FTP PIDs. You can, for example, control the purge and vent valves, if it comes to that.

P.S. @John Williams: I don't want to "hijack" your thread with too much unwanted "OBD nerd" talk, so feel free to let me know if you've lost interest and I'll "cease & desist".

 

[John Williams]

curious, are you having issues with the EVAP system on this 2008 Grand Prix?

Yes, it's my kids car and she told me that the check engine light was on, so after scanning, it came up with a large EVAP leak code. That's when I started poking around and trying to educate myself on how the system works and what data PIDs were available which ultimately led me here. I'm really surprised at how much help you two are willing to supply.
When I get the car back I'm going to try to get that PID for the FTP sensor reporting properly.

 

[John Williams]

You can, for example, control the purge and vent valves, if it comes to that.

Yeah, if you are willing to help me along, I'd really like to be able to do as much with the tool as possible. I was under the impression that "bi directional " functions were not possible with a simple Scanner dongle??

 

[AmpOverload]

I was under the impression that "bi directional " functions were not possible with a simple Scanner dongle??

So-called "bi-directional" operations are actually possible with even the simplest and least expensive scantools. But it can be a bit tricky, depending on a lot of "variables". Basically though, you have to have a way to send commands to and receive replies from the scantool, typically using a (free) Bluetooth "terminal emulator" app (or your existing app if it is flexible & capable enough). And you need knowledge of the vehicle-specific commands that control the EVAP valves (which I can help with).

Just to see what's possible with even a measly $14 Bluetooth scantool, take a peek at this post (skip to the part where I say, "As for Mode $08"), where I mention a simple Android app that I wrote for a 2004 Buick Century to do EVAP diagnosis.

But even without direct valve control, you can often see what's happening by monitoring the appropriate EVAP-related PIDs as the vehicle undergoes the usual EVAP test. If the 2008 Grand Prix is anything like the 2004 Buick Century, then it will run the EVAP test (assuming the engine is started "cold", the fuel tank is between about 15 to 85% full, and there are no other disqualifying DTCs [Diagnostic Trouble Codes]) shortly after engine start. That graph I posted earlier is a good example of what you should see, but there are other PIDs to monitor that can make things clearer.

Unfortunately, I'm not familiar with the details of how the 'Car Scanner' and 'OBD Fusion' apps work. But clearly, given that you posted a graph, at least one of them supports it, so that's a good start.

Of course, sometimes all this "electronic" diagnosis will come to no avail and you'll wind up needing to do a "smoke test" to find an EVAP leak. But even there, the bi-directional control is useful because you'll need to close the (normally open) vent valve at some point while "smoking" the system.

P.S. If you decide to get into this, we'll likely need to know what engine type the 2008 Grand Prix has (L26, L32, or LS4). Also, it's always more useful to report the specific DTC (e.g. P0455) rather than the human-readable description (which can vary).

 

[John Williams]

.S. If you decide to get into this, we'll likely need to know what engine type the 2008 Grand Prix

Yes, definitely would like to keep the conversation going on this as I've got three GM vehicles all in the 2000 year era that I'm trying to keep on the road for my wife and kids. I've toyed with the idea of buying a halfway decent scan tool but have a hard time justifying the $500 to $700 bucks , also looked into the Chinese knock off Tech2 scanner but have read they are hit and miss and can require some computer skills (which I don't have) to get the program to run . I've got a good quality adapter (OBDlink MX+) that I use along with their app. If you have any recommendations on scanner apps,let me know as I'm always willing to try new ones out. I've the got "Torque lite" that works decent on my phone and wanted to upgrade to the pro version but it won't download because I get a notification that my phone is too new??

Thanks again for all your help .

 

[AmpOverload]

Yes, definitely would like to keep the conversation going on this as I've got three GM vehicles all in the 2000 year era that I'm trying to keep on the road for my wife and kids. I've toyed with the idea of buying a halfway decent scan tool but have a hard time justifying the $500 to $700 bucks , also looked into the Chinese knock off Tech2 scanner but have read they are hit and miss and can require some computer skills (which I don't have) to get the program to run .

Not having computer skills will probably hinder how far you can go with this, but it really depends on your own comfort level and motivation. But there's nothing stopping you from doing the "easy" stuff first, like graphing various PIDs to monitor vehicle behavior as the EVAP test runs. Bi-directional commands might be unwise until/unless you gain some comfort level and experience with sending commands directly to the scantool with one of the aforementioned Bluetooth "terminal emulator" apps. It's really up to you. Whatever you decide to do, be assured that you don't require a lot of expensive hardware or software to do it.

I've got a good quality adapter (OBDlink MX+) that I use along with their app.

I have several scantools, including the older (non-'+') "OBDLink MX Bluetooth" scantool and have been quite happy with it, so I think your choice of scantools will serve you well, both now and into the future. The cheap $14 Bluetooth scantool I referred to earlier works great with older GM (and Ford) vehicles but is considerably less useful on many newer vehicles, GM and otherwise.

If you have any recommendations on scanner apps,let me know as I'm always willing to try new ones out. I've the got "Torque lite" that works decent on my phone and wanted to upgrade to the pro version but it won't download because I get a notification that my phone is too new??

As for software, I've run Torque Lite on occasion, but I typically have little experience with the popular Android OBD2 apps. I write my own simple Android apps when I want phone/tablet access to the vehicles that I work on. I think that your issue with not being able to upgrade Torque Lite to Torque Pro is likely the app's author not having kept up with all the maddening changes that Google forces upon their "Play Store" apps as newer Android versions are released. (Another reason why I prefer to write my own Android apps -- no forced upgrades or changes required!)

As for the vehicle's EVAP issues, if it were me, I'd start by gaining as much familiarity with the 2 apps you have: "Car Scanner" and "OBD Link". Can you graph multiple PIDs simultaneously with either of those apps? If so, I'd start by graphing these PIDs:

• Mode $22 PID $1297 ("Fuel Tank Pressure", equation "signed(A*256+B)/1024", in units of "inches H2O")
• Mode $22 PID $1312 ("EVAP Test State", equation "A", no units)

Start monitoring with the engine off and "cold" (i.e. first start of the day), with between 15% and 85% fuel. And, be sure to report here with a full list of the actual DTCs that the vehicle is reporting. Then graph & monitor those 2 PIDs. You should see the PID $1312 ("EVAP Test State") value report 0. Start the engine. The "EVAP Test State" will probably change pretty quickly from 0 to 1 (meaning "Test Running"). Wait a few minutes and you should see the "FTP" value go from around zero to about 10 (inches H2O). If the FTP graph doesn't look something like the one I posted, you will have begun to confirm the problem.

Be aware that the vehicle will typically only run the EVAP test once, right after the 1st "cold" start of the day, so you have to "have your ducks in a row" when you start the engine for the 1st time!

If you progress that far, two more PIDs that are good to monitor during EVAP testing include:

• Mode $22 PID $1107 ("Evap Vent Solenoid Command", equation "bit(A,2)", no units, 0="venting", 1="not venting")
• Mode $22 PID $1170 ("Evap Purge Solenoid Duty Cycle", equation "A/255*100", in units of "percent")

I'm not sure exactly how to specify equations in "Car Scanner" or "OBD Link" but I'm sure that can be figured out. @TJBaker57's experience with "OBD Fusion" would probably be relevant for "OBD Link" and I think he uses "Car Scanner" too and he always has good, useful advice.

 

[TJBaker57]

have any recommendations on scanner apps,let me know

Car Scanner ELM OBD is the way to go. The developer is continually updating the app as opposed to Torque Pro which has lagged behind the times for quite a long time now.

Car Scanner is fairly effortless at logging data, can selectively review the data later (when you are not driving), can export and share the logfiles for others to review, and so on.

Car Scanner has also added a PID (sensor) scanner that while tricky to set up can help in identifying what PIDs are supported by a given vehicle. The PID scanner cannot say what data a given PID reports, but it at least establishes what PID numbers are available.

 

[John Williams]

View attachment 115709

Okay, let the dumb questions begin!!
I have created this PID #1297 per your instructions and it does work, however it returns a result of "64" which is obviously not correct, so just wondering about what would need to be in the "metric to English scale factor and Metric to English offset"??
For whatever reason I'm not able to select anything in either of the Metric or English units fields either??

 

[AmpOverload]

I have created this PID #1297 per your instructions and it does work, however it returns a result of "64" which is obviously not correct, so just wondering about what would need to be in the "metric to English scale factor and Metric to English offset"??

As far as "Metric to English", you really should not have to worry about that because this PID's native units are "inches of H2O". But I might be missing something.

Just for the record, a "scale factor" and "offset" would be used, as just one example, to convert degrees Celsius to degrees Fahrenheit. The metric value would be multiplied by your "scale factor" (9/5) and then have your "offset" (32) added to it.

It's possible that the app uses a different set of rules to specify the "equation" than what I've posted. EDIT: It seems to be 'OBD Link'. Which app is this? And what does it show when you press "Test"? EDIT: (i.e. anything more than just "64"?)

 

[John Williams]

Okay, thanks for the reply. This is the OBDlink app, and when I hit test it confirms that the request succeded and then shows the results which was 64.

 

[AmpOverload]

Okay, thanks for the reply. This is the OBDlink app, and when I hit test it confirms that the request succeded and the shows the results which was 64.

Based on @TJBaker57's notes earlier in this thread, I suspect you should try this for the equation:

int16(combine(A,B))/1024

 

[TJBaker57]

The PID list included:

1. Mode $22 PID $114E is "Fuel Tank Pressure" in volts, using the formula "A/256*5".
2. Mode $22 PID $1297 is "Fuel Tank Pressure" in native units of "inches H2O", using the formula "signed(A*256+B)/1024".

The following likely does NOT apply to the present case but instead applies to the P10 PCM used in 2002-2005 Vortec 4.2 GMT360/370.

I spent some time yesterday looking over the available PIDs, $1297 is not supported. I thought maybe there would be an alternate. There is not.

I captured the serial traffic while the scantool readout out the emissions data. I varied the fuel tank pressure sensor return signal manually with a 10 turn linear potentiometer. Only a single byte varied in the serial traffic while both values varied on the scantool.

So when one of my 2 scantools reports Emissions data for a 2002-2005 P10 PCM that includes both Fuel Tank Pressure in both volts and separately In/H2O (or kPa or mm/Hg) both fields must be the result of the single #114E PID.

I have been hammering away at equations for the Fuel Tank Pressure in In/H2O or mm/Hg or Pascals, etc. using the value from PID $114E.

I can duplicate the readout of a Tech 2 but I have reservations about the accuracy of the Tech 2 display itself. ie: the two units offered by the Tech 2 don't precisely agree with each other.

I have been trying to ascertain a resolution per bit and haven't nailed down something that satisfies all the unit display possibilities seen in my 2 scantools

Granted, the level of accuracy I am chasing here doesn't really matter, but I like to get to the actual bottom of things.

 

[AmpOverload]

For the record, I just did the same experiment, but with Tech2Win (configured as a 2002 Trailblazer with "S" engine) and my HVS (Hardware Vehicle Simulator).

Only a single byte varied in the serial traffic while both values varied on the scantool.

I see the same thing. When I vary only what the sim is sending for what Tech2Win shows as PID $114E, I see both the values (pressure units and voltage) vary on Tech2Win's 'EVAP Data' display, strong evidence that there is only 1 "FTP" PID on P10 PCMs, despite there being 2 distinct PIDs on the P04 PCMs.

I can duplicate the readout of a Tech 2 but I have reservations about the accuracy of the Tech 2 display itself. ie: the two units offered by the Tech 2 don't precisely agree with each other.

I see that too. At 3 different test settings (0.0, 2.5, and 5.0 volts), the "mmHg" value does not equal the equivalent "in H2O" value, using the conversion factor of 1.8682738033. That looks like a Tech2/Tech2Win bug to my eye, and it's not the 1st we've seen as I suspect you may recall.

On a different topic...

The equation "language" for OBD Fusion (and, hence, OBD Link, I presume) seems rather poorly documented. The vendor has this page:

https://obdsoftware.my.site.com/s/article/user-defined-pids

But it doesn't mention the "combine" function. So, @TJBaker57, just curious how you knew to use that. And do you happen to know if this:

(A*256+B)

would work equally well as this:

combine(A,B)

 

[John Williams]

For whatever it's worth, I've tested PID # 1297 with equation
"For tank/evap pressure in Pascals:
int16(combine(A,B))/4" and got numbers from appx 20 to 700 while using OBDLINK, I then switched over to the Car Scanner app and used the "Evap pressure in Pascals " PID that has always worked and got very similar numbers, however they were negative which is what I assume they should be.

 

[TJBaker57]

doesn't mention the "combine" function. So, @TJBaker57, just curious how you knew to use that. And do you happen to know if this:

Within the app PID editor there is a help button....

 

[AmpOverload]

For whatever it's worth, I've tested PID # 1297 with equation
"For tank/evap pressure in Pascals:
int16(combine(A,B))/4" and got numbers from appx 20 to 700 while using OBDLINK, I then switched over to the Car Scanner app and used the "Evap pressure in Pascals " PID that has always worked and got very similar numbers, however they were negative which is what I assume they should be.

Since this 2008 Pontiac supports that Mode $01 PID $32 ("Evap System Vapor Pressure"), you might as well use it. If you can record and graph that with Car Scanner, then start the cold engine and hopefully the EVAP test will run and you'll see a graph like I showed.

The "sign" (positive or negative) of the values is not nearly as important as the range of values it reports throughout the EVAP test. Some sources call the thing being measured "pressure" and typically report it as negative values. Other sources will refer to it as "vacuum" and report it as positive values. Seeing how the graph behaves is what you're really looking for. You should see vacuum being pulled within about 4 minutes after you start the engine. Then the vacuum will slowly "decay". Then the vacuum will quickly disappear once the vent valve is opened.

EDIT: Also, a friendly reminder: it would be helpful to know the engine details on this Grand Prix as well as a complete list of current DTCs (Diagnostic Trouble Codes).

 

[John Williams]

Sorry for dropping the ball on the car specifics.
It is a 2008 Pontiac Grand Prix 3.8 liter L26 motor, no air pump, W body.
As of now there are no DTC trouble codes stored. I may or may not have solved the issue as while doing a little inspecting, I noticed quite a bit of corrosion around the fuel filler neck so I sanded it back down to bare metal and also cleaned and inspected the fuel cap. I haven't been able to get to the car when in a cold state so have not ran the test yet as you described above.

 

[AmpOverload]

I may or may not have solved the issue as while doing a little inspecting, I noticed quite a bit of corrosion around the fuel filler neck so I sanded it back down to bare metal and also cleaned and inspected the fuel cap.

Funny that you mention that! I had been meaning to mention that and forgot, since that's a common source of EVAP leaks and is often a quick solution. But even if that's the solution, you're better prepared now to deal with any EVAP problems that might arise on this or any other similar vehicle in the future.

I'll keep my fingers crossed that it works for you and your daughter. But if not, or even if so but you're just interested in doing more testing, just let us know!

And thanks for the engine & DTC details. That's always useful, in almost every diagnosis. For example, when I run Tech2Win to find PIDs for a vehicle, I almost always have to supply some details about the engine and/or other components and I hate to make guesses!