P0455 and some other questions about fuel tank

[TJBaker57]

By Jove, I think you've got it! That will be great to try out and be able to confirm one way or the other if the valves are cooperating with the PCM. Based on what I know at this point I see that as quite an accomplishment to get bi-directional control from a simple bluetooth dongle and app! What's even greater is having this kind of information on a public forum for the benefit of others as well.

Public,,,, to a point.

I have reservations about divulging the specific instructions in public so I will be private messaging you the actual message to send.

These instructions are highly specific to THIS PCM and perhaps even THIS platform. Sending such an instruction on a different PCM could have disastrous results. I wish not to be a part of that possibility.

How to send said messages is more of a feature of Car Scanner and Torque Pro as well so that much can be described here without concern.

When constructing a "sensor" as Car Scanner calls them one of the selections is for what type of entry are we building. Car Scanner labels this a "Decode Scheme". By far the most common is "Formula".



Among the choices is "Action PID". An action PID is placed in a "Dashboard" and when tapped it sends the message specified as the "Command" along with the header entered directly below the Command. Additional strings can be included by entering them in the entries below as "Start Diagnostics ..." and "Stop Diagnostics....".

In the images I posted, "Purge_100%", "close_vent" and "EVAP_Leak_Test" are all Action PIDS I created in the "Sensor" editor. Since I am not sending a "Test Tool Present" message periodically these actions will expire in about 5 seconds as seen on the graphs. This is a safe way of doing this for now.

The other displays are simple "Formula" Sensors like the one you just set up for Fuel Tank Pressure.

Torque Pro can do similar with the use of "Buttons" on a Dashboard if memory serves. I had a Torque Pro Dashboard with a button that would command the engine cooling fan to 100% for a short time.

Now then, an important note. If I tap the "close_vent" Action PID display the instruction message is sent and the "EVAP_Vent" display will toggle from "0" to "1". All this means is the PCM has activated the driver for that circuit. It will do this even if the PCM is sitting on a bench with no wiring for said vent solenoid present.

You would need to listen for the vent activating preferably back nearby the vent location. I can hear it in the drivers seat but only for one of the two actions, closing or opening. I forget which makes more noise.

With a running engine and the purge valve closed I saw no difference in Fuel Tank Pressure when I closed the Vent. (seen in 1st image)

On another test after the truck had idled for some time I noted the PCM had opened the purge valve at a little more than 10% duty. That time when I closed the vent valve I could see a small increase in Fuel Tank Pressure voltage (vacuum). I also noted the PCM adjusted the purge valve duty cycle lower, likely due to increased fuel vapors altering the fuel mixture.

Have you setup a purge valve sensor yet?

 

[dhanger]

Public,,,, to a point.

I have reservations about divulging the specific instructions in public so I will be private messaging you the actual message to send.

These instructions are highly specific to THIS PCM and perhaps even THIS platform. Sending such an instruction on a different PCM could have disastrous results. I wish not to be a part of that possibility.

I see, it hadn't occurred to me that this could be dangerous going to a PCM of another type vehicle, I can understand your caution. Didn't mean to put you in an uncomfortable position, just got over-enthusiastic...

You would need to listen for the vent activating preferably back nearby the vent location. I can hear it in the drivers seat but only for one of the two actions, closing or opening. I forget which makes more noise.

Exactly what I was planning initially.

Have you setup a purge valve sensor yet?

No, I hadn't seen that in Car Scanner standard issue pid's, nor was it in azswiss's spreadsheet, so thanks for posting the setup for that.

I'll start setting up a screen in Car Scanner for the testing, haven't done much of that so that will be a good exercise for me.

 

[TJBaker57]

I'll start setting up a screen in Car Scanner for the testing, haven't done much of that so that will be a good exercise for me.

Setting up Car Scanner Dashboards can be quite confusing to say the least. Sooo many options for the display, colors, background colors, fonts. It can be maddening trying to find where a particular detail is located.

More often I use the live data option for my activities but that doesn't allow the use of Action PIDs I believe. Saved Dashboard pages work well for this task.

hadn't seen that in Car Scanner standard issue pid's, nor was it in azswiss's spreadsheet

I very likely have a lot of stuff that just never got published. That Purge valve PID/Sensor actually came initially from a .csv of extended GM PIDs included with Torque Pro. Much of those early PID/Sensor definitions came from hobbyists and as such they contain some errors. There is one that is actually labeled "H2OS" instead of "HO2S" sensor (Heated Oxygen Sensor).

Both Torque Pro and Car Scanner ELM OBD (and likely others) have a means of importing .csv files containing all the definitions of PID/Sensors eliminating the drudgery of manually entering large numbers of said PID/Sensors.

I feel that initially it is better to create a few PID/Sensors to become familiar with these 'inner workings'.

 

[dhanger]

Now then, an important note. If I tap the "close_vent" Action PID display the instruction message is sent and the "EVAP_Vent" display will toggle from "0" to "1". All this means is the PCM has activated the driver for that circuit. It will do this even if the PCM is sitting on a bench with no wiring for said vent solenoid present.

Clarification: when toggling 'close vent' I do get a response on the evap vent sensor that toggles to 1 (on) then off after 5 seconds as you described. Is the vent sensor response actually coming from the PCM or just 'syncing' with the command, if you get my meaning? I ask because when I toggle 'close vent' I get no response physically from the vent solenoid--no sound, no action with my hand on it even. I'm not eager to point the finger at that just yet since we're still working on this test. All along I had been thinking to myself that the vent valve actuation not likely to be the problem but the whole point of this test was to confirm, and now it's looking more positively that is indeed the problem. Recall that I have confirmed the solenoid action by bench testing multiple times and it does seal well as confirmed by my earlier FTP test graph, so I give the solenoid itself a clean bill of health.

 

[TJBaker57]

Clarification: when toggling 'close vent' I do get a response on the evap vent sensor that toggles to 1 (on) then off after 5 seconds as you described. Is the vent sensor response actually coming from the PCM or just 'syncing' with the command, if you get my meaning? I ask because when I toggle 'close vent' I get no response physically from the vent solenoid--no sound, no action with my hand on it even. I'm not eager to point the finger at that just yet since we're still working on this test. All along I had been thinking to myself that the vent valve actuation not likely to be the problem but the whole point of this test was to confirm, and now it's looking more positively that is indeed the problem. Recall that I have confirmed the solenoid action by bench testing multiple times and it does seal well as confirmed by my earlier FTP test graph, so I give the solenoid itself a clean bill of health.

The vent status toggling from 0 to 1 indicates ONLY that the internal electronics of the PCM that ground the vent solenoid in order to close the vent have been activated.

Even if there were no actual wiring connected between the PCM and the vent solenoid that vent status would still toggle from 0 to 1.

So it looks like there is either a break in the control wiring between the vent solenoid and the PCM or perhaps a break in the wire that supplies the 12 volt positive to the vent solenoid.

Have you ever tested for a 12 volt signal at the vent solenoid with key at RUN??

Engine Controls Diagram 9 — 2004 Chevrolet TrailBlazer 4WD L6-4.2L VIN S Service Manual | Operation CHARM

Detailed repair manual for the 2004 Chevrolet TrailBlazer 4WD L6-4.2L VIN S.

charm.li

 

[dhanger]

Fuse 26 underhood. As soon as I realized I may have a break I looked up the wiring diagrams and found fuse 26 blown. Replaced it and now the vent valve is working. Don't know why the fuse was blown so I may be dealing with that again in the future.

Never ceases to amaze me how I never seem to look in the right place first, LOL. Like saying 'I found it in the last place I looked'.

If you don't mind I would like to continue with the purge valve command so I can run a full test like you did earlier.

 

[TJBaker57]

No, I hadn't seen that in Car Scanner standard issue pid's, nor was it in azswiss's spreadsheet, so thanks for posting the setup for that

Well that EVAP Purge sensor may not work for you. I just reviewed my listing of what PIDs work for each year and I see that PID 1170 does not seem to be supported by the 2004 and 2005 PCMs. I will look to see what PID DOES work for 2004 P10 PCMs.


Just checked and for 2004 and 2005 GM used something similar to an SAE Standard OBDII PID for EVAP Purge Duty Cycle.

If you have been trying to get the purge valve duty sensor working.... edit the "117001" to read "002E01" instead.

 

[TJBaker57]

found fuse 26 blown.

I wondered about that but was reluctant to ask if you had checked that !!

 

[dhanger]

Well that EVAP Purge sensor may not work for you. I just reviewed my listing of what PIDs work for each year and I see that PID 1170 does not seem to be supported by the 2004 and 2005 PCMs. I will look to see what PID DOES work for 2004 P10 PCMs.


Just checked and for 2004 and 2005 GM used something similar to an SAE Standard OBDII PID for EVAP Purge Duty Cycle.

If you have been trying to get the purge valve duty sensor working.... edit the "117001" to read "002E01" instead.

I haven't actually tried the purge sensor yet so I'll check on that. But I was referring to the purge command, like the vent command you PM'd me, so that I can do a complete check on the system before I clear the code and start over.

I wondered about that but was reluctant to ask if you had checked that !!

Sometimes your mind just gets stuck in a rut. Part of the problem is when I started this I knew literally nothing about how the evap system worked so I had to spend a lot of time studying up on it, and of course numerous YT videos with literally nobody pointing at the fuses and circuits--I probably would have run into that eventually.

 

[TJBaker57]

I haven't actually tried the purge sensor yet so I'll check on that. But I was referring to the purge command, like the vent command you PM'd me, so that I can do a complete check on the system before I clear the code and start over.



Sometimes your mind just gets stuck in a rut. Part of the problem is when I started this I knew literally nothing about how the evap system worked so I had to spend a lot of time studying up on it, and of course numerous YT videos with literally nobody pointing at the fuses and circuits--I probably would have run into that eventually.

A fuse blowing may point to a component which may be failing and drawing too much current.

Later PCMs are capable of monitoring that circuit and setting a code specifically for just such a electrical defect like the blown fuse.

 

[dhanger]

According to the schematic both the purge and vent valves are on the same fuse (10A). Since the vent valve worked fine after fuse replacement it's possible the purge valve may be drawing excessive, or both together may overload the fuse. Anyway I'm sure I'll find out soon enough--it may be time to replace both valves, they are OEM so more than 20 years old.

 

[TJBaker57]

According to the schematic both the purge and vent valves are on the same fuse (10A). Since the vent valve worked fine after fuse replacement it's possible the purge valve may be drawing excessive, or both together may overload the fuse. Anyway I'm sure I'll find out soon enough--it may be time to replace both valves, they are OEM so more than 20 years old.

I have a little gadget I bought at Harbor Freight. I can plug it in where a fuse goes and it reads out the current passing through. I had to make adapter for it as it was made to fit the larger blade type fuses. Maybe I will test my solenoids current draw.

 

[dhanger]

I have a little gadget I bought at Harbor Freight. I can plug it in where a fuse goes and it reads out the current passing through. I had to make adapter for it as it was made to fit the larger blade type fuses. Maybe I will test my solenoids current draw.

Interesting, got a link? Does it have setting for limiting current? Wouldn't want to plug it in and allow excess current through a circuit.

 

[TJBaker57]

Interesting, got a link? Does it have setting for limiting current? Wouldn't want to plug it in and allow excess current through a circuit.

Not certain they still sell it. It has a 30 amp max and a fuse for that.



looks like they have a newer updated version..

https://www.harborfreight.com/30-amp-fuse-slot-circuit-amperage-draw-measurement-tool-70079.html

Anyway, I just tested mine and with both the purge at 100% and the vent activated the draw was only 1.1 amp.

 

[dhanger]

Anyway, I just tested mine and with both the purge at 100% and the vent activated the draw was only 1.1 amp.

That's along the line of what I would expect from a couple of small coils.

 

[budwich]

just measure the resistance of the coils of the units in question. You will get an idea of the draw from that based on a 12v system.

 

[dhanger]

Final followup (hopefully): Didn't have time to work on the problem over the weekend so I was waiting until today to do some testing with the settings that @TJBaker57 set me up with so I could see if there was anything else I would need to do after fixing the fuse. There's a regional park 2 miles up the road where I go 3 times a week for a short hike, so this morning I got in and started up and saw that the CEL was still on (I didn't expect anything different, was going to clear the code later and see how it went) then headed up to the park. When I got there as I was shutting off I glanced at the dashboard and lo and behold the CEL had turned off! I had assumed it would have taken longer with more driving cycles before this.

With the new charcoal canister I no longer have fumes while standing near the car, went for a fillup and no more spitting, yay! I suppose I could have gotten more life from the old canister with the evap system working now, but I'm not sorry I changed it--can't go back now anyway since I chopped up the old one to see inside (hey, don't we all do that now and then LOL).

Too bad I didn't think of the fuse sooner but like I said before I had to spend a lot of time just understanding the system, what does what and why and how so I don't feel too bad about not thinking of that sooner. Upside is that I learned something new and that's always a good thing.

Thanks to everyone who contributed, especially to TJBaker for all the Car Scanner help!

 

[TJBaker57]

Upside is that I learned something new and that's always a good thing

If you're interested I can fairly easily put together a file of sensor definitions for import to Car Scanner. We have quite a few that are specific to the GMT360/370 platform and are otherwise not available in Car Scanner or Torque Pro.

 

[dhanger]

If you're interested I can fairly easily put together a file of sensor definitions for import to Car Scanner. We have quite a few that are specific to the GMT360/370 platform and are otherwise not available in Car Scanner or Torque Pro.

Speaking only for myself I'm considering upgrading to one of the inexpensive bi-directional scanners being marketed these days, this experience has really shown me the value of one. I've been looking particularly at reviews of the xTool A30M unit but I'm going to spend some time looking at others in the same range of affordability in the 'prosumer' market (don't hear that term much anymore).

No doubt there are others who would really benefit from having a compilation of Car Scanner PID's and if I decide to stick with it anyway it would be great for me too. I was thinking of asking you about it and wanted to offer any help you might need--I'd be happy to work on a spreadsheet similar to the one that @azswiss did, just let me know.

BTW I couldn't get either of the purge valve entries for Car Scanner to work (both the sensor and the command), even after your update in post #47. I had planned on looking at that some more today but now I don't need it so it would just be an academic exercise.

Thanks,
Dan

 

[TJBaker57]

BTW I couldn't get either of the purge valve entries for Car Scanner to work

Curious the sensor didn't work. Wonder if early or late 2004 was different than the 2004 PCM I have. And the PID (002E) is what a Tech 2 calls for a 2004 purge valve solenoid duty cycle.

Just for reference I thought I would show what a restricted EVAP circuit looks like. My Yukon has had this for a couple years now. One of these days I'll take a look at it.



It can be readily seen that when the PCM attempts 100% purge the vacuum builds in the tank until it passes the threshold that the PCM thinks is OK. The PCM cuts off the purge valve in response to this too-high vacuum. The cycle repeats over and over and over.

I wonder if these newer scantools sold today have the ability to graph things in this way.

 

[dhanger]

Curious the sensor didn't work. Wonder if early or late 2004 was different than the 2004 PCM I have. And the PID (002E) is what a Tech 2 calls for a 2004 purge valve solenoid duty cycle.

I don't know if it would make a difference but I no longer have the OEM PCM installed. About a year ago I contacted Lime Swap about tuning and got recommendations for a junkyard module. Apart from the same model year the only other requirement was the axle ratio, which I cross referenced with the RPO list. I was able to locate the correct one and sent that in for tuning, then put the OEM module on the shelf for emergencies. All that to say that the car is not using the OEM module but the replacement should be identical to my knowledge--but maybe that's a factor, IDK.

It can be readily seen that when the PCM attempts 100% purge the vacuum builds in the tank until it passes the threshold that the PCM thinks is OK. The PCM cuts off the purge valve in response to this too-high vacuum. The cycle repeats over and over and over.

I wonder if these newer scantools sold today have the ability to graph things in this way.

The xTool A30M is supposed to be able to graph 8 individual PID's at one time which is one of its claims over its equivalent competitors which mostly only do 4 at one time. 8 would make for a pretty messy graph so to my thinking it should be more than enough for anything I would ever want to do. I ordered the scanner so I'll be spending some time with that soon.

 

[mrrsm]

If you need to look at these issues from a dedicated, "Old School" Snap-On Vantage Pro Graphing Multi-Meter point of view... Here are just a few screens of the -=entire=- EVAP Systems Diagnostics. .. including what a Known Good EVAP Purge Valve Wave Form Oscilloscope Signature should look like when compared with whatever your other Diagnostic Scan Tools produce upon the screen for the actual performance on your 2004 Chevrolet Trailblazer:

 

[TJBaker57]

don't know if it would make a difference but I no longer have the OEM PCM installed. About a year ago I contacted Lime Swap about tuning and got recommendations for a junkyard module. Apart from the same model year the only other requirement was the axle ratio, which I cross referenced with the RPO list. I was able to locate the correct one and sent that in for tuning, then put the OEM module on the shelf for emergencies. All that to say that the car is not using the OEM module but the replacement should be identical to my knowledge--but maybe that's a factor, IDK.

Ahhh !! That actually does open a lot of possibilities. I believe (??) Jeremy could have used any operating system and calibration from 2002 to 2005 for your 2004 engine. That could alter the PID for the EVAP Purge valve duty cycle.

I would think that one of the two PIDs I suggested, 1170 or 002E, should have worked. According to Tech 2 firmware 2002 and 2003 provided PID 1170, 2004 and 2005 provided 002E. Puzzling.

The xTool A30M is supposed to be able to graph 8 individual PID's at one time which is one of its claims over its equivalent competitors which mostly only do 4 at one time. 8 would make for a pretty messy graph so to my thinking it should be more than enough for anything I would ever want to do. I ordered the scanner so I'll be spending some time with that soon.

I used to be able to have any number of PIDs in a Car Scanner graph but it looks like they have now imposed a limit of about 25 now. It's just as well because the refresh rate drops with each additional PID scanned. The snippet I posted shows about 10 minutes out of about 2 hours of driving data where I had about 7 PIDs recorded. If I display on just one graph it does indeed get confusing/messy.

 

[Mooseman]

The way tuning works is that the tuner uses whatever OEM tune is on the PCM and modifies it, which is then flashed back onto the PCM. Unless the tuner turns off a particular function or error codes, pollution controls function the same as stock. Since you are getting a P0455, that means the Evap system was not modified.

 

[TJBaker57]

that means the Evap system was not modified

However, there appears to be no PID for the Purge Valve duty cycle. This will cause a Tech 2 to fail when trying to view live data for the engine.

 

[dhanger]

Ahhh !! That actually does open a lot of possibilities. I believe (??) Jeremy could have used any operating system and calibration from 2002 to 2005 for your 2004 engine. That could alter the PID for the EVAP Purge valve duty cycle.

I would think that one of the two PIDs I suggested, 1170 or 002E, should have worked. According to Tech 2 firmware 2002 and 2003 provided PID 1170, 2004 and 2005 provided 002E. Puzzling.

I wanted to respond to this before I consider the topic has run its course. I decided to contact Jeremy to get a little understanding of his process regarding the OS as that's another new concept to me (in the context of a PCM that is). Here was his response, which didn't really clear much up for me:

Hi Daniel, think of the OS -the operating system- as an analogue to a computer OS such as windows or linux. Its not the application that -say- calculates spark advance, but it runs the program that calculates spark advance. In general, every engine, every year got a new or updated OS. My tuning software checks the VIN against the OS before reading and writing to make sure the file is valid.

So I don't really know how all that relates to the PID's under consideration but it occurred to me it might be instructive to temporarily swap the OEM module back in just to see how it responded. But...before I got to that I noticed something I hadn't before--when looking over the invoice for my tune I noticed that the VIN on the invoice was for the junkyard module which I had sent him, which of course made sense. I started to wonder if that would cause any issues, like selling the car (which I have no intention of at this point anyway) but something more important came to mind--during emission testing I always noticed that the tech would always take the printout and compare the VIN on the test printout with the actual VIN on the dash, so I think I'm going to have to do something about that. My thinking is to send Jeremy the OEM module to repeat the same tuning and put it back in, leaving the junkyard module the spare. I hate to spend the money but it's probably good insurance. Anyway I won't be pursuing any more scanner issues until I get that taken care of and then I'll start playing around with it afterwards.

For now I'm happy that my P0455 is in the rear view mirror now--that was last Monday and wouldn't you know it on Friday I got a new, unrelated code come up! But if I have problems with that I'll start a new topic.

 

[TJBaker57]

the tech would always take the printout and compare the VIN on the test printout with the actual VIN on the dash, so I think I'm going to have to do something about that

You can check the VIN currently in the PCM using Car Scanner. Connect to the vehicle then on the Car Scanner main screen select "Terminal".

Enter ATS1 and press enter.

Enter 0902 and press enter.

You should get something like this image...