PO442

[mrrsm]

Here are some images of the P10 PCM C1, C2 & C3 Pin-Out Locations:


Post #4... Via THIS Link:

BCM pinout

Looking to pick up on the reverse lamp circuit at the BCM. I've found sources that indicate it may be a light green wire, but there are several of them back there. One of which is a com wire that didn't take kindly to having a test light on it... anyone have a pinout for the connectors or a...

gmtnation.com

 

[budwich]

You then use the posted table (back at the start) to determine your fuel level. As Tjbaker57 posted earlier about the voltage reading, you can check that by measuring voltage for the same pins on the other cable (disconnected in the video from the one that was probed). Go from your results. While you are at it, ensure your meter connections are good and do some "rattle and shake testing" of the connector wiring to see if things are stable or not... ie. checking for looseness / flaky connections.

 

[Stuntmanmike1977]

Sure glad I checked back. Easy enough will do that as soon as the New England weather lets up. Also, I had to put more gas in cause now it keeps wanting to stall so, I fill the neck to the top and have to rock the truck back and forth then you can hear the gas gurgling into the tank. Will the new aluminum filler neck assembly fix that or, just if it's leaking? Really don't want to cut open a new tank. The original valve is free, just won't go in.thanks for simplifying the test procedure. I will post back when I get some numbers.

 

[Stuntmanmike1977]

Got nothing on the 200 ohm setting.

 

[Stuntmanmike1977]

On this setting I got.256?

 

[budwich]

:-( you need to post exactly which pins and connector that you are trying to test just to clear.

As far as doing a resistance measurement, you need to be on one of the "numbered" scales (ie. 200, 2k, etc).

IF you were testing exactly like the posted video, and you got "nothing"... what does your "nothing" mean. Post a picture of the meter to help with clarity. To further test your understanding, put the meter on the 200 ohm scale and touch the probes together, the reading should go to "0"... is that your "nothing" reading?

 

[TJBaker57]

On this setting I got.256?

That meter setting is for testing diodes.

use the "2K" setting.

 

[Stuntmanmike1977]

:-( you need to post exactly which pins and connector that you are trying to test just to clear.

As far as doing a resistance measurement, you need to be on one of the "numbered" scales (ie. 200, 2k, etc).

IF you were testing exactly like the posted video, and you got "nothing"... what does your "nothing" mean. Post a picture of the meter to help with clarity. To further test your understanding, put the meter on the 200 ohm scale and touch the probes together, the reading should go to "0"... is that your "nothing" reading?

No, I had it on the 200,ohm scale and got literally nothing like the meter wasn't even hooked up.

 

[Stuntmanmike1977]

No, I had it on the 200,ohm scale and got literally nothing like the meter wasn't even hooked up.

I even tried inserting small pieces of wire in the terminals cause my meter proves might be too big and still read nothing.

 

[mrrsm]

How about this... Let me drop in all of these images and see if what is available becomes helpful to you. If not...The Mods can delete them. Note that these Images are consecutive in the order they appear on the Snap-On Vantage Pro Tool as Step-By-Steps and pertain to your particular Vehicle:

The First Batch of 20 Diagnostic Images:



More to Follow...

 

[mrrsm]

Second Batch of 20 Images:

 

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Third Batch of 20 Images:



More To Follow...

 

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Fourth Batch of 20 Images:



More To Follow...

 

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Fifth Batch of 20 Images:



Last Batch of Images to Follow...

 

[mrrsm]

Last Batch of Images:

 

[Stuntmanmike1977]

Thank you for the images. Your images say these procedures are for a 2005 GMC Sierra, does that matter? Also, I've never used a scan tool in my life. I do not have access to the fuel pump/sender connector. You want me to test the voltage for the vent solenoid in the back? What is the voltage supposed to be at the pump so maybe I can put gas in it? Only takes half a gallon at a time, rock the truck back and forth then can hear it gurgle out of the filler and into the tank. The only thing I might be able to test is the new pressure sensor and vent valve. Unless I had better training I could understand the images a little better I guess. This truck is acting so ridiculous. I know it can be frustrating to try and explain some things to someone who has absolutely no diagnostic equipment or experience. I'm trying though.

 

[Stuntmanmike1977]

I even tried inserting small pieces of wire in the terminals cause my meter proves might be too big and still read nothing.

Yep, tried the wire small enough to go all the way in and still no reading.

 

[Stuntmanmike1977]

Will try again tomorrow.

 

[Aroc]

Sure glad I checked back. Easy enough will do that as soon as the New England weather lets up. Also, I had to put more gas in cause now it keeps wanting to stall so, I fill the neck to the top and have to rock the truck back and forth then you can hear the gas gurgling into the tank. Will the new aluminum filler neck assembly fix that or, just if it's leaking? Really don't want to cut open a new tank. The original valve is free, just won't go in.thanks for simplifying the test procedure. I will post back when I get some numbers.

Just to cover all bases, is the filler hose line free of restrictions? I recently fixed a deteriorating rubber hose line causing a small leak when I filled up with gas so I recommend checking for restricted flow from just the filler neck to the tank entry check valve to be sure it is free flowing.

 

[Aroc]

Would anyone happen to know if the PCM uses the fuel tank capacity that is stored in the PCM when it comes to calculating the fuel level?

Off topic but I found something interesting when filling up my late 2002 ENVOY (June build). The PCM fuel level% is accurate at low level but maxes out at 90% at overfull tank levels. The Dash gage is accurate at both low and full levels. I would think a full tank with correct fuel sender output (confirmed 250ohms before install) would read out 100% from PCM regardless if 18.7gal or 22gal tank.

 

[budwich]

No, I had it on the 200,ohm scale and got literally nothing like the meter wasn't even hooked up.

I also posted that you needed to check your meter by touching the probes together to see that the meter is working properly.

Further, your reading on the 200 scale might have been correct as the resistance might have been higher than the that range. You need to try each range to see what reading gets shown.

 

[mrrsm]

Okay... I've done as you asked and what follows will be Nine Consecutive Posts covering 20 Images per Page (Max) with 2 on the Last page for a total of 162 Images describing all of the diagnostic elements of the Evap and Fuel System Components.... short of getting into the EFI Diagnostics

The reason there are so many Screen Prints is because contrary to the popular prejudice... the GMT360 Fuel and Evap Systems Diagnostics are a great deal more involved (and interesting) than most of us would imagine and the Cautions and Tech Notes explanations they include here are a great help with improving the overall understanding of "The Works".

Since this is your Thread, if you want to dispense (remove) with the Full Size Truck Images I posted previously... No Problem. They would probably be better placed in the Full Size Truck Section I suppose if there is an interest there on the subject. So...Here Goes...

20 Image Batch (First of Nine):

 

[mrrsm]

20 Image Batch (Second of Nine):



More To Follow...

 

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20 Image Batch (Third of Nine):



More To Follow...

 

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20 Image Batch (Fourth of Nine):



More To Follow...

 

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20 Image Batch (Fifth of Nine):



More To Follow...

 

[mrrsm]

20 Image Batch (Sixth of Nine):



More To Follow...

 

[mrrsm]

20 Image Batch (Seventh of Nine):



More To Follow...

 

[mrrsm]

20 Image Batch (Eighth of Nine):



Last Two Images to Follow to complete the Full Set...

 

[mrrsm]

These Last Two Images Complete this Full Set... (Ninth of Nine Image Batches)

 

[mrrsm]

On the subject of the "Where and How...?" To Probe Harness Connectors...

When NOT using a pair of Probe Leads directly coming from the DMM to take Measurements RIGHT AT the Disconnected Component's Contact Pins...



The Best Practices for the uses of any DVOM, any DMM or any Oscilloscope is to either Actively Back-Probe the Outside (Back Side) of the Electrical Connectors between the Light Green Weather-Packing and the various Color ID'd Plastic Wire Insulation using Pin Probes like these depicted for inexpensive purchase over on Amazon, by passing them closely alongside the Weather-Pack Sheaths you can get the Thin Metal Probes into Direct Contact with the individual Wire-To-Pin interfaces deep inside of these Connectors...

https://www.amazon.com/back-probe-pins/s?k=back+probe+pins

...or... As an alternative technique, use instead, Direct Wire Probes that literally Penetrate the Wire Insulation in order to access the shielded Copper Wire and make a VERY Direct Circuit Connection on LIVE or STATIC Systems that MUST have the Component Connectors properly installed on the Vehicle. These are usually of a "Puncture and Screw Down TIGHT" Style of Wire Harness Probe.

https://www.amazon.com/dp/B0CS3K59NZ/?tag=gmtnation-20

In the Case of either making Low Amperage Measurements with a Loop Fuse Replacement or via Fuse Buddy Replacement Inserts or via Re-Settable Fuse Switches that stand in for the inconvenient Fuses that will quite often Burn Out during Testing...THESE are Very Convenient Temp Replacements:

Amazon.com

Amazon.com

Lastly, for the indirect sensing of High Voltage Circuits, such as on COP (Coil Over Plugs) or when Diagnosing the Wave Forms of Spark Plugs and picking their signals up via a Lead Clamp, there are Paddle Probes that can function without the need to make direct contact with the Circuit to sense their High Energy Electrical Fields of the Primary and Secondary Coils... and thus... Never have to open or touch these High Energy Circuit Components:

"Best Results can often be SEEN ...Whenever Viewed ...on an Oscilloscope SCREEN..."

https://www.amazon.com/dp/B08153JDVS/?tag=gmtnation-20

 

[TJBaker57]

On the subject of the "Where and How...?" To Probe Harness Connectors...

When NOT using a pair of Probe Leads directly coming from the DMM to take Measurements RIGHT AT the Disconnected Component's Contact Pins...

View attachment 113729View attachment 113730

The Best Practices for the uses of any DVOM, any DMM or any Oscilloscope is to either Actively Back-Probe the Outside (Back Side) of the Electrical Connectors between the Light Green Weather-Packing and the various Color ID'd Plastic Wire Insulation using Pin Probes like these depicted for inexpensive purchase over on Amazon, by passing them closely alongside the Weather-Pack Sheaths you can get the Thin Metal Probes into Direct Contact with the individual Wire-To-Pin interfaces deep inside of these Connectors...

View attachment 113735View attachment 113733
View attachment 113732View attachment 113734

https://www.amazon.com/back-probe-pins/s?k=back+probe+pins

View attachment 113716View attachment 113717View attachment 113718

...or... As an alternative technique, use instead, Direct Wire Probes that literally Penetrate the Wire Insulation in order to access the shielded Copper Wire and make a VERY Direct Circuit Connection on LIVE or STATIC Systems that MUST have the Component Connectors properly installed on the Vehicle. These are usually of a "Puncture and Screw Down TIGHT" Style of Wire Harness Probe.

https://www.amazon.com/dp/B0CS3K59NZ/?tag=gmtnation-20

View attachment 113719View attachment 113731
View attachment 113720View attachment 113721

In the Case of either making Low Amperage Measurements with a Loop Fuse Replacement or via Fuse Buddy Replacement Inserts or via Re-Settable Fuse Switches that stand in for the inconvenient Fuses that will quite often Burn Out during Testing...THESE are Very Convenient Temp Replacements:

Amazon.com

View attachment 113724View attachment 113725

Amazon.com

View attachment 113722View attachment 113723

Lastly, for the indirect sensing of High Voltage Circuits, such as on COP (Coil Over Plugs) or when Diagnosing the Wave Forms of Spark Plugs and picking their signals up via a Lead Clamp, there are Paddle Probes that can function without the need to make direct contact with the Circuit to sense their High Energy Electrical Fields of the Primary and Secondary Coils... and thus... Never have to open or touch these High Energy Circuit Components:

"Best Results can often be SEEN ...Whenever Viewed ...on an Oscilloscope SCREEN..."

https://www.amazon.com/dp/B08153JDVS/?tag=gmtnation-20

View attachment 113726View attachment 113727View attachment 113728

Update: I used Google Lens to locate a similar image, the "Fuse Buddy" with 3 adapters.


I can't seem to successfully find a link to this item. I already have a harbor freight version of the tester on the far left but it did not come with any adapters. I searched without success for what appears to be be circled in this screenshot...

 

[mrrsm]

This is the one that appears right now over on Amazon... and with a 23% reduction in price... it's listed below for $36.00:

https://www.amazon.com/dp/B083TCDQBH/?tag=gmtnation-20

Here is that ES308B variant for around the same price:

Amazon.com

 

[TJBaker57]

This is the one that appears right now over on Amazon... and with a 23% reduction in price... it's listed below for $36.00:

https://www.amazon.com/dp/B083TCDQBH/?tag=gmtnation-20

Here is that ES308B variant for around the same price:

Amazon.com

This has been my workaround..

 

[Stuntmanmike1977]

I probed the fuel sender unit connector again and can only get a reading on 2K scale I believe and got a fluctuating resistance reading of .580-.590

 

[budwich]

OK... as you can see from the tables (and from spec... 250 ohm equals full), that your connection is showing more resistance than a "normal full".... BUT its not totally a "broken circuit" because it is not "infinite".

Do you actually know (guess) how much fuel that you have in the tank?
IF you have extra hands or bodies, you could try measuring well people "rock the boat" to see if things change any.

My guess (without a tank drop) is you have a poor / rusted connection along the route and / or "rooted" cable.

Added was rethought

 

[Stuntmanmike1977]

I would say right now I probably have about 4-5 gallons in the tank. After rocking the truck a bunch of times to empty the filler neck into the tank, I measured right after I rocked it and it went up to 1.284 on the 2k scale before settling down to .580. I just got done tearing out the entire neck assembly taking it all apart and made sure there ino restrictions even pulled a clean wad of shop rag through it with a piece of wire. And the tank valve is free. Again vent valve and pressure switch are brand new. As to why it still won't take fuel and looking over all the images, I'm still stumped. However the other day I was PBblasting the tank strap bolts and while I was under there I banged on the bottom of the tank where the fuel pump is and to me it sounded like the float arm was bouncing around in there. There a way I can test it from the relay socket and how can I test to see if the vent valve is working? What is a rooted cable?

 

[Stuntmanmike1977]

I would say right now I probably have about 4-5 gallons in the tank. After rocking the truck a bunch of times to empty the filler neck into the tank, I measured right after I rocked it and it went up to 1.284 on the 2k scale before settling down to .580. I just got done tearing out the entire neck assembly taking it all apart and made sure there ino restrictions even pulled a clean wad of shop rag through it with a piece of wire. And the tank valve is free. Again vent valve and pressure switch are brand new. As to why it still won't take fuel and looking over all the images, I'm still stumped. However the other day I was PBblasting the tank strap bolts and while I was under there I banged on the bottom of the tank where the fuel pump is and to me it sounded like the float arm was bouncing around in there. There a way I can test it from the relay socket and how can I test to see if the vent valve is working? What is a rooted cable?

So what I know is the gauge says it's full and maybe the computer thinks it's full.

 

[mrrsm]

@TJBaker57 ... Re: Post #154... I think I figured out WHY that Kit was not showing up on the searches... The OEM Parts Packaging Manifest and Instructions Sheet was using a DIFFERENT Kit Part Number. I took some *Fresh Fotos* to clarify for everyone what's actually inside the Kit (and the Kaboodle).

 

[budwich]

You can test your theory about the comp causing something based on the gas tank full... ie. closing a valve or otherwise which is causing a filling problem. I don't think there is such a "program state".
Anyway, get your self a lamp bulb (ie. 12v automobile lamp). Measure the resistance to ensure it is "reasonable". Hook some wires to it (maybe buy a cheap socket and bulb at harbor freight or equivalent). Take the wires and hook it to the socket that is the PCM side of the socket that you were testing with the meter previously. The pcm will now see the lamp resistance and should shows "empty" or otherwise depending on the resistance of the bulb. Try fill your tank with your gas can there after. Go from the result.

Other than changing your fuel gage reading, I don't think anything else will be any different. You have an "onion skin" problem here.