Power to a swiched fuse with key off

Mooseman

Moderator
I'm really leaning towards deleting all posts before this one as they were in the totally wrong direction. The wrong schematics have been used since the beginning so we were not working on the right thing at all.

Attached is a printout PDF from GM-SI and is IRREFUTABLE as being correct for a 2006 TB. Fuse 26 IS ALWAYS POWERED. FULL STOP. FUSE 26 IS NOT AT FAULT. END OF STORY. It's doing what it's supposed to do.

Forget about fuse 26 for now. You have to do a parasitic draw test. This video is pretty good except for a few things:

  • To disable the interior light, I would use a screwdriver to close the door latches with the doors open.
  • When you first connect the MM to the battery, it may spike in amps for a few minutes as modules power up. Wait for several minutes to let everything go back to sleep
  • For your first initial test, pull fuse 26. If that doesn't drop the amps, then it's not at fault. Put it back in.
  • Remove the 125A megafuse to eliminate, or point to, the rear fuse box.
  • Pull one fuse at a time until the amps drop.

Report back with the amps being drawn and if you found the faulty circuit.
 
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Blueking25

Blueking25

Well-Known Member
I'm really leaning towards deleting all posts before this one as they were in the totally wrong direction. The wrong schematics have been used since the beginning so we were not working on the right thing at all.

Attached is a printout PDF from GM-SI and is IRREFUTABLE as being correct for a 2006 TB. Fuse 26 IS ALWAYS POWERED. FULL STOP. FUSE 26 IS NOT AT FAULT. END OF STORY. It's doing what it's supposed to do.

Forget about fuse 26 for now. You have to do a parasitic draw test. This video is pretty good except for a few things:

  • To disable the interior light, I would use a screwdriver to close the door latches with the doors open.
  • When you first connect the MM to the battery, it may spike in amps for a few minutes as modules power up. Wait for several minutes to let everything go back to sleep
  • For your first initial test, pull fuse 26. If that doesn't drop the amps, then it's not at fault. Put it back in.
  • Remove the 125A megafuse to eliminate, or point to, the rear fuse box.
  • Pull one fuse at a time until the amps drop.

Report back with the amps being drawn and if you found the faulty circuit.
I did this and the meter read 3.20
I'm going to have to buy some adapters or something because my battery I a side post screw in and I tried to tape the leads on so I could pull fuses but nothing worked for me. So I have to figure out how to keep the leads attached. They have to been on there good for me to get a solid reading.
 
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Blueking25

Blueking25

Well-Known Member
I'm really leaning towards deleting all posts before this one as they were in the totally wrong direction. The wrong schematics have been used since the beginning so we were not working on the right thing at all.

Attached is a printout PDF from GM-SI and is IRREFUTABLE as being correct for a 2006 TB. Fuse 26 IS ALWAYS POWERED. FULL STOP. FUSE 26 IS NOT AT FAULT. END OF STORY. It's doing what it's supposed to do.

Forget about fuse 26 for now. You have to do a parasitic draw test. This video is pretty good except for a few things:

  • To disable the interior light, I would use a screwdriver to close the door latches with the doors open.
  • When you first connect the MM to the battery, it may spike in amps for a few minutes as modules power up. Wait for several minutes to let everything go back to sleep
  • For your first initial test, pull fuse 26. If that doesn't drop the amps, then it's not at fault. Put it back in.
  • Remove the 125A megafuse to eliminate, or point to, the rear fuse box.
  • Pull one fuse at a time until the amps drop.

Report back with the amps being drawn and if you found the faulty circuit.
I removed the 125 mega fuse and tested and the meter read zero, but that's what it should read because now there are no cables attached to the fuse box.
 

budwich

Well-Known Member
Interesting.... it is good to see that the fuse is hot all the time as suspected at the start. Too bad it took so long to get to that outcome. Guess the "red herring" was caught. :smile: Good luck on the drain issue.... they are always tough. The circle continues. 😄
 

budwich

Well-Known Member
you might consider looking a little closer at the transmission codes (pending or otherwise) to see if there is some hint of a stuck solenoid or something like that which could be a source of draw.
 

Mooseman

Moderator
I removed the 125 mega fuse and tested and the meter read zero, but that's what it should read because now there are no cables attached to the fuse box.
So if it's reading right, that would tell me it's something in the rear fuse box that's drawing. What is the current draw with the fuse in?

Edit: OK, saw that the draw is 3.20. Is that AMPS? If it is, that is really high. What scale are you using on the MM?
 
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Maverick

Member
I removed the 125 mega fuse and tested and the meter read zero, but that's what it should read because now there are no cables attached to the fuse box.
Like Mooseman has mentioned the 125 fuse only supplies power to the Rear fuse block. The front is powered as long as the terminals are connected to the battery.

For holding your lead in place you might try a short bolt and washer and thread it in to clamp your meter probe in place where your cable normally goes.

Maybe Mooseman can confirm but looks like the transmission circuit is a switched circuit so it probably wont be the source of your problem.
 
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Blueking25

Blueking25

Well-Known Member
you might consider looking a little closer at the transmission codes (pending or otherwise) to see if there is some hint of a stuck solenoid or something like that which could be a source of draw.
All the transmission solenoid are new from ACDELCO. The transmission was back to working great until I restored power to the evap solenoid. I didn't have the draw problem until I got power to the evap solenoid. I left the 26 fuse in last night plus the evap solenoid plugged in and I have a dead battery this morning. So that's 2 nights 26 fuse plugged in I wake up to a dead battery. The 2 days I took the fuse 26 out I woke up to a fully charged battery.
 
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Blueking25

Blueking25

Well-Known Member
So if it's reading right, that would tell me it's something in the rear fuse box that's drawing. What is the current draw with the fuse in?

Edit: OK, saw that the draw is 3.20. Is that AMPS? If it is, that is really high. What scale are you using on the MM?
I followed the video you sent me. That's less draw then Eric had and his was from just a little dome light.
 

Mooseman

Moderator
Maybe Mooseman can confirm but looks like the transmission circuit is a switched circuit so it probably wont be the source of your problem.
Yes it is.
 

Attachments

Mooseman

Moderator
Are you following our instructions and requests? It's difficult to keep helping if you don't do as requested. We're trying to go in a methodical manner to eliminate things now that we have the correct schematics.

You have to do a proper parasitic draw test. You can pull fuse 26 first if you want but it has to be done. If it is fuse 26, then I would disconnect the PCM and do another draw test. If the draw does drop, then I would be looking at the PCM as being faulty if it's sending ground to the solenoid when it's not supposed to.
 

budwich

Well-Known Member
IF fuse 26 (and subtending circuit) is a candidate for the drain, just disconnect the "new wire" at the fuse, place your meter on "current reading" and connected in between the fuse output and the new wire. It will now read how much draw is happening. Go from there.
 
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Blueking25

Blueking25

Well-Known Member
Is the wiring diagram you have specific to the VIN of your truck?
Ok so first I'M SUPER GRACIOUS FOR EVERYONE'S TIME AND HELP!!!
Second the only thing I really pride myself on is treating others how I'd like to be treated. With that being said I don't argue or try to be a know it all.
So whether I'm in a bind or not I'm the same thankful either way. AND IM DEFINITELY IN A BIND! LOL....
I've spent ALOT of money at the Chevy dealership in the last month. So I went down there to see if they would throw me a bone.
Luckily the guy is cool and he grabbed 1 of the techs he said was of the better. The guy ran my vin in the Chevy system and this is from the software he said they all use daily to repair, program, flash and update the vehicles that come in.
**

Circuit/System Description

An ignition voltage is supplied directly to the evaporative emission (EVAP) canister purge solenoid valve. The EVAP canister purge solenoid valve is pulse width modulated (PWM). The scan tool displays the amount of ON time as a percentage. The control module monitors the status of the driver. The control module controls the EVAP canister purge solenoid valve ON time by grounding the control circuit via an internal switch called a driver....


His opinion was that the transmission solenoid wasn't recieving power.
And he believes I'd get lucky and find out why fuse 26 is hot all the time if I could find out why the transmission pink wire wasn't recieving power, especially since they are in the same wire bundle.

With all this being said I'd like to know what you guys think.

THANK YOU A MILLION AGAIN!!!!

Ed
 
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Blueking25

Blueking25

Well-Known Member
Are you following our instructions and requests? It's difficult to keep helping if you don't do as requested. We're trying to go in a methodical manner to eliminate things now that we have the correct schematics.

You have to do a proper parasitic draw test. You can pull fuse 26 first if you want but it has to be done. If it is fuse 26, then I would disconnect the PCM and do another draw test. If the draw does drop, then I would be looking at the PCM as being faulty if it's sending ground to the solenoid when it's not supposed to.
Really confused on why you would ask that as everything asked of me I've done!
I do everything ALL of you ask! Most of the time several times!!!!!!
I also have to work!.

But I spend several hours on this truck daily, most of the time til 2 to 4 in the morning. And learning and studying as I go along. I just don't jump into things unless I have an ideal what I'm doing.
I'm not being rude again! But I'm not retired and I'm single with a huge client list that trust and depend on me.
 
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Mooseman

Moderator
OK, it might look like we're getting PO'd but we're not. I think we're just as frustrated as you are. You may be doing it but I think we're lacking details as to results you're getting. So far, these are what's missing:
  • a complete parasitic draw test. Which circuit dropped?
  • if fuse 26 dropped amps?
  • if it was fuse 26, draw test result of unplugging the PCM
  • if disconnecting the new wire stops the draw (@budwich )
I'll be the first to admit that we don't know everything but neither does the dealer.

Circuit/System Description

An ignition voltage is supplied directly to the evaporative emission (EVAP) canister purge solenoid valve. The EVAP canister purge solenoid valve is pulse width modulated (PWM). The scan tool displays the amount of ON time as a percentage. The control module monitors the status of the driver. The control module controls the EVAP canister purge solenoid valve ON time by grounding the control circuit via an internal switch called a driver.
Sorry but I think he's wrong here. It could be an error in their software. I looked at the schematics for 2005 and, just like the 2006 Rainier, it was switched by ignition. The 2006 TB is not switched. It could have been old info in the description. Could have been the same thing in AllData.

His opinion was that the transmission solenoid wasn't recieving power.
He's probably right about that one. Or wiring. Seen that lots of times here.

And he believes I'd get lucky and find out why fuse 26 is hot all the time if I could find out why the transmission pink wire wasn't recieving power, especially since they are in the same wire bundle.
It's hot all the time because it's supposed to. If the tranny pink wire isn't getting power, then that's something else. It does have its own fuse. So that would need a circuit check.

But we need to fix your current draw first. Tranny is a separate issue in my opinion.
 
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Blueking25

Blueking25

Well-Known Member
OK, it might look like we're getting PO'd but we're not. I think we're just as frustrated as you are. You may be doing it but I think we're lacking details as to results you're getting. So far, these are what's missing:
  • a complete parasitic draw test. Which circuit dropped?
  • if fuse 26 dropped amps?
  • if it was fuse 26, draw test result of unplugging the PCM
  • if disconnecting the new wire stops the draw (@budwich )
I'll be the first to admit that we don't know everything but neither does the dealer.



Sorry but I think he's wrong here. It could be an error in their software. I looked at the schematics for 2005 and, just like the 2006 Rainier, it was switched by ignition. The 2006 TB is not switched. It could have been old info in the description. Could have been the same thing in AllData.



He's probably right about that one. Or wiring. Seen that lots of times here.



It's hot all the time because it's supposed to. If the tranny pink wire isn't getting power, then that's something else. It does have its own fuse. So that would need a circuit check.

But we need to fix your current draw first. Tranny is a separate issue in my opinion.
I'm trying to get someone to hold the probes on the terminals to do the draw test. Its seems like I have to really have them on there good for the draw number to stay steady. I've tried tape and clamps but neither worked.
I live with just my dog and even though he's a great companion he's not great at helping.
I think it was mentioned to use a bolt and nut to hold them in place, I'm working on getting that stuff now. This battery has side screw in post.
 

Mooseman

Moderator
It's a common SAE bolt size (can't remember the size). For the terminal, maybe just a wire held with locking pliers would work or a battery clamp.
 

budwich

Well-Known Member
Blueking25.... I think you have given us "almost enough" information to finally nail this. 😄

First, you are convinced that the circuit associated with fuse 26 is causing a significant drain such that the battery is dead "quickly". Good, accepted, then this should be your focus.

Next, remember that you provided us with the resistance measurement leaving the fuse towards ground... it was around 140-180 ohms (not solid). Even with simple electrical math, this means a draw of about 6-9 ma.... which isn't really enough to kill a battery although it might add to an already "marginal load" (another story / issue). So what does this mean? Well, you need to do one more resistance measurement... basically, the same one but this time also having the pcm disconnected from the circuit... the result should be "open / infinity". IF it is not, you have found your likely problem on this "circuit"... being somewhere from the fuse output to the pcm cable connector.

IF this latest resistance is "infinity", then this potentially means that there is some sort of issue at the pcm itself... either internally or maybe at the connector (contamination). To support this "theory"... one explanation about the "140-180" ohm measurement ( which might be low)... this measurement is done using a meter "supply" of a few volts to measure the resulting current flow to "meter calculate" the resistance. However, this low "meter voltage" may not be enough to actually cause a "breakdown" of the electrical components inside the adjoining pcm circuit (ie. things like "weak" FET's, diodes, capacitors,etc). Hence, even thought the metered resistance, that you see may be somewhat OK, the operational resistance at "12 volts" maybe quite difference due to component "breakdown".

Anyway hope you understand what I have said. I think you are close and with the little extra test, you may have a better "guess" at where the problem lies. Please note, the reason for doing this test like this, resistance as opposed to current, is that potentially a current test may damage your meter IF the current goes large (more than 10 amps in most cases).

Lastly, and somewhat related, if indeed, your PCM has some sort of internal issue, this may reflect on others areas "indirectly" which could be why you had some of the other codes pop up.

That's my story for your story. Hope the rain ends soon and you can get further on this.
 
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Blueking25

Blueking25

Well-Known Member
Blueking25.... I think you have given us "almost enough" information to finally nail this. 😄

First, you are convinced that the circuit associated with fuse 26 is causing a significant drain such that the battery is dead "quickly". Good, accepted, then this should be your focus.

Next, remember that you provided us with the resistance measurement leaving the fuse towards ground... it was around 140-180 ohms (not solid). Even with simple electrical math, this means a draw of about 6-9 ma.... which isn't really enough to kill a battery although it might add to an already "marginal load" (another story / issue). So what does this mean? Well, you need to do one more resistance measurement... basically, the same one but this time also having the pcm disconnected from the circuit... the result should be "open / infinity". IF it is not, you have found your likely problem on this "circuit"... being somewhere from the fuse output to the pcm cable connector.

IF this latest resistance is "infinity", then this potentially means that there is some sort of issue at the pcm itself... either internally or maybe at the connector (contamination). To support this "theory"... one explanation about the "140-180" ohm measurement ( which might be low)... this measurement is done using a meter "supply" of a few volts to measure the resulting current flow to "meter calculate" the resistance. However, this low "meter voltage" may not be enough to actually cause a "breakdown" of the electrical components inside the adjoining pcm circuit (ie. things like "weak" FET's, diodes, capacitors,etc). Hence, even thought the metered resistance, that you see may be somewhat OK, the operational resistance at "12 volts" maybe quite difference due to component "breakdown".

Anyway hope you understand what I have said. I think you are close and with the little extra test, you may have a better "guess" at where the problem lies. Please note, the reason for doing this test like this, resistance as opposed to current, is that potentially a current test may damage your meter IF the current goes large (more than 10 amps in most cases).

Lastly, and somewhat related, if indeed, your PCM has some sort of internal issue, this may reflect on others areas "indirectly" which could be why you had some of the other codes pop up.

That's my story for your story. Hope the rain ends soon and you can get further on this.
Sorry I'm not good at explaining things or even communicating for that matter so PLEASE don't take this the wrong way, and I'm not being rude but the ONLY THINGS I'm convinced of is I have a problem that I'm probably making it harder on myself because I don't know exactly what to do or how to precisely do it.
And the other thing I'm convinced of is I need help!
With that being said I somewhat understand what you are saying.
Are you saying I need to buy a new pcm? If not could you please explain a little more exactly what you are saying I should do?
I'm definitely going to do the draw test for mooseman.
Also the tests I've done have been with the pcm hooked up and taken out of the truck with the same results. Does that matter at all?

Also this probably has been addressed before so I'm sorry if it has. But I just want to get it out my head. The evap vent valve next to the gas tank is tied into fuse 26 and the purge solenoid. When I back probe it I have 12 volts at both wires. I know I'm not supposed to. And wonder if I had a short somewhere in the wires that run the length of the truck would that be causing any of my problems? Or am I getting the wrong readings because of what's going on up front?
If it's not an issue or nothing to worry about please just say so and I'll forget about it.
 

Mooseman

Moderator
It is normal, when the ground side circuit is open (ground not sent to the solenoid by the PCM), that you would see 12v+ on both sides of the solenoid connector. The solenoid is basically a wound wire inside so gives continuity, kinda like a light bulb.

I'm also leaning towards the PCM. Since you are having issues to do a draw test (not because you're incapable but issues with battery connector), what you could do as a test would be to leave fuse 26 in and disconnect the PCM overnight to see if your battery gets drained. This should completely open the ground side of the solenoid circuit.
 

budwich

Well-Known Member
Sorry I'm not good at explaining things or even communicating for that matter so PLEASE don't take this the wrong way, and I'm not being rude but the ONLY THINGS I'm convinced of is I have a problem that I'm probably making it harder on myself because I don't know exactly what to do or how to precisely do it.
And the other thing I'm convinced of is I need help!
With that being said I somewhat understand what you are saying.
Are you saying I need to buy a new pcm? If not could you please explain a little more exactly what you are saying I should do?
I'm definitely going to do the draw test for mooseman.
Also the tests I've done have been with the pcm hooked up and taken out of the truck with the same results. Does that matter at all?

Also this probably has been addressed before so I'm sorry if it has. But I just want to get it out my head. The evap vent valve next to the gas tank is tied into fuse 26 and the purge solenoid. When I back probe it I have 12 volts at both wires. I know I'm not supposed to. And wonder if I had a short somewhere in the wires that run the length of the truck would that be causing any of my problems? Or am I getting the wrong readings because of what's going on up front?
If it's not an issue or nothing to worry about please just say so and I'll forget about it.
Look... I can see that we / you are getting no where along with further frustration.
I know that you are being pulled in multiple directions which makes things even tougher. It took a multitudes of posts to come to the "realization" that powering going into the fuse is RIGHT with HOT AT ALL TIMES. That caused a lot of "circle chasing". The ultimate problem that you were having with "fuse 26" was NOT one of powering but of CIRCUIT DRAIN in the whole car but you have emphatically stated is directly associated with the CIRCUIT subtending fuse 26. That's great. The focus should be there until you can rule things out.

Further, I suggested, a while back for you to do a resistance test on the circuit. It took a long while to get there. You tried doing continuity tests and other things instead of following the suggested test which was from the "new wire" to a "KNOWN GROUND" (an example was given to perhaps use the negative battery connection).

When you FINALLY followed up with the results of this resistance test, we got an answer of "140-180" ohms that was not stable. That is suspicious as an "open / high" resistance was expected. This test got lost in the "long winding thread" because of the "back and further" about powering and such. The forum / me never looked long at that result within the context of a DRAIN. At the time, without a schematic of the circuit especially one for the YEAR AND VEHICLE type, things were lost.

So as a I mentioned, just previous post, the result of your resistance measurement is that the current draw BASED ON MATH is about 6-9 MILLIAMPS.... this is NOT very much BUT IT IS A MATH CALCULATION and not an actually current measurement which fine.

At this point, I have asked you to do one more resistance measurement exactly as before ... at the NEW WIRE (removed from the fuse block) to a KNOWN GROUND (ie. negative battery terminal) with the PCM disconnected. This test is simple and DOES NOT NEED multiple "hands" as you seem to indicate is an issue with other tests. That's all you need to do and post the results.

I am not sure how much more can be explained at this point. You have suggested things like "back probing" and such. Those are OK but NOT what is being asked. Further, you "state" what's in the circuit coming off of fuse 26 BUT you miss a significant FACT that there is a COMPLEX PCM involved in the circuit that has "UNKNOWN CIRCUIT MAKEUP" (ie. its a "black box") so its response is somewhat "unknown" outside of what has been posted... ie. it SHOULD be either an "OPEN or GROUNDED" BUT what you don't know / understand is how this condition is achieved. The first resistance test likely tells you that it is NOT ACHIEVED in the "OPEN" case... because the resistance is NOT INFINITE.

LASTLY, I have never asked you to replace anything including the PCM. Without doing testing as suggested, that would likely be a waste. Further, I suspect now that this thread has had more "Oh, I did this and I also have this, etc", it is likely that at the very start, you were chasing a problem whereby you replaced the fuse box for NOTHING (as subsequently the replacement did NOT improve anything).... look at the title.

I am sorry if you take this post wrong, but hopefully you get the issue addressed in a timely fashion... at least that is my hope.

One last edit: the "draw test" that mooseman suggested, is an "equivalent" to the resistance tests... in essence not using a meter and waiting for time and a dead battery to tell you something. However, note that drawing a conclusion that your PCM is bad directly from the result (even the resistance test) is potentially a bad conclusion.
 
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Mooseman

Moderator
Which is why I suggested he disconnect the PCM as an overnight test. You could also pull fuse 26, use a couple of small wires in the fuse connectors and measure the amps across the terminals. DO NOT SHOVE THE MM LEADS INTO THE FUSE CONNECTORS. You will destroy them. Or better yet, use a blown fuse.
 

budwich

Well-Known Member
I don't disagree with the "draw test"... what I disagree with is that after doing the "disconnect the PCM" draw test, that you can instantly say your PCM is bad. That is not necessarily the right conclusion directly from that test result.
 

Mooseman

Moderator
Oh for sure. Just going through the process of elimination. Could also be a bad connection. It would really narrow it down.
 

budwich

Well-Known Member
yes... as I have said... do the test(s) and based on the results, go from there. BUT make sure you are pretty sure before replacing parts which can get expensive especially as the part in focus is the PCM. Anyway, there are a few others things to check before pointing the finger at the pcm.... but one can go there when the time comes.... :smile:
 

Mooseman

Moderator
If there's a pick-a-part nearby, PCM's can be had pretty cheap. Just a security relearn and good to go. I agree, parts shotguns should be banned :biggrin:
 
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Blueking25

Blueking25

Well-Known Member
If there's a pick-a-part nearby, PCM's can be had pretty cheap. Just a security relearn and good to go. I agree, parts shotguns should be banned :biggrin:
Sorry guys! I'm having some health issues. I suffer from really bad migraines. And it's just me and my dog so when I have them I have to pretty much deal with them myself. And most of the time I can barely get up from the bathroom floor until the migraine let's up a little. They make me throw up and dry heave really bad. I usually can't do much for a couple days, it's actually hard typing this. But I'm going to try and get back at it tomorrow.

Thank you sincerely for all the time and help.

Ed
 

Mooseman

Moderator
Take care buddy and I feel your pain. I had them for 20+ years and I was the same. Only narcotics would work for me. So thankful that I have outgrown them.
 

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