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2003 GMC Sierra blowing pcm fuse


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Lindsayw790
Novice

Apr 25, 2018, 12:14 PM

Post #1 of 14 (245 views)
2003 GMC Sierra blowing pcm fuse Sign In

My truck keeps blowing the pcm 20amp fuse.this truck I just bought and there is a power wire that is only long enough to reach fuse box under hood and I can't figure out exactly where it goes . It has a eye hole conecter on it. Any ideas or suggestions?


Discretesignals
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Apr 25, 2018, 1:41 PM

Post #2 of 14 (231 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

Which series, engine size, 2 or 4wd?

Does it blow the fuse only when you turn the ignition on? Got a picture of the wire?





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Lindsayw790
Novice

Apr 25, 2018, 7:19 PM

Post #3 of 14 (213 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

It blows the fuse after it starts. I've figured out the wire placement but the fuse still is blowing.when I'm turning the truck over it seems like it's dragging like low battery would but the battery is fine. It's the V6 2wd model . The recent owner replaced the starter thinking it was it but it was the fuse after all lol. But this fuse has bin a way bigger pain


(This post was edited by Lindsayw790 on Apr 25, 2018, 7:23 PM)


Tom Greenleaf
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Apr 26, 2018, 12:47 AM

Post #4 of 14 (203 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

Quote >"when I'm turning the truck over it seems like it's dragging like low battery would but the battery is fine.<"
What makes you so sure the battery is all fine? Battery alone might test fine but if not cranking at a normal speed it's not getting enough power "delivered" or engine is just too hard to turn. Just that it doesn't matter if the engine was sitting on a crate on the floor you have to find out why it doesn't crank properly first IMO or all bets off on anything else,


T



Discretesignals
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Apr 26, 2018, 3:35 AM

Post #5 of 14 (197 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

So the fuse doesn't blow with the ignition on engine off?





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Lindsayw790
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Apr 26, 2018, 7:10 PM

Post #6 of 14 (183 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

 the fuse only blows when the engine is running sometimes for a little bit I might get 20 minutes out of it sometimes. I found a ground strap attached to chassis but hanging it is located directly under the fill pipe on frame. Would this cause my problem and where should it be attached to. I figured fill spout but it seems like a main ground seens it's a strap and all? Is there a big ground for the fuel pump or tank itsself ? And what's a way of testing the fuel pump to see if it's the cause of the fuse.


(This post was edited by Lindsayw790 on Apr 26, 2018, 7:13 PM)


Tom Greenleaf
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Apr 26, 2018, 10:08 PM

Post #7 of 14 (178 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

Lindsayw790: Is this truck rusty in general like most are? Back to root causes of this crap either way you just got it apparently with this problem now found the ground strap to fuel neck which isn't grounded without that intact time to check all grounds (many all over the thing) that they are intact. If there's no return (grounding) of power just as strong as power to anything it will seek any which way it can to try to. The fuel neck is plain dangerous - take care of that no guessing fix that.


You have that unknown wire just left open find out where it goes and was for that's not OE style now yours to figure out what and why it's there.
Starter, battery you originally said they are fine or starter replaced does the same thing time to test voltage drops and all the spots where just plain battery power and grounds do things first. Battery cables have stunk for ages older than this need to check both ends of each starters don't drag like a bad one or low power for no reason now probably not a good main engine ground nor great primary body to engine block ground(s) there are a few at least some may be just bare braided wire with those eyelet ends obvious things or hidden for interior things.
You just got it - right? It had this problem and prior owner stopped at a new (rebuilt) starter apparently is possibly no good or back to not able to get power and ground from and back to battery - this first it doesn't really matter what this is yet if all that is screwed up.
This and most any vehicle machine THE #1 power consumption is cranking the engine and it can't do that well. Till that works up to speed nothing else is going to matter much - yet.


Try another battery known good I just don't know on this one nor the starter let some testing and live data on battery observed or just try another as said fully charged up first really helps the show,


T



Lindsayw790
Novice

Apr 27, 2018, 5:47 PM

Post #8 of 14 (155 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

Thanks for info muchly appreciated


Discretesignals
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Apr 28, 2018, 12:31 PM

Post #9 of 14 (128 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

This might be difficult to figure out without using inductive amp clamp and an oscilloscope to measure the actual current that is flowing through different circuits that that fuse protects. You should inspect the wiring for the O2 sensor heaters. Another thing that can cause a fuse to blow like that is a fuel pump that is drawing excessive current as it is running.

I don't have a wiring schematic for that circuit at the moment. I'm on vacation, but if you can get hold of one that helps a lot to see what different devices are protected by that fuse.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Apr 28, 2018, 12:34 PM)


Hammer Time
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Apr 28, 2018, 2:46 PM

Post #10 of 14 (118 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

You were asked this question many responses ago and I still don't see an answer.


Quote
Which series, engine size, 2 or 4wd?




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Apr 28, 2018, 3:57 PM

Post #11 of 14 (115 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

Did say above >"It's the V6 2wd model .<"
?
Tom


Hammer Time
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Apr 28, 2018, 4:32 PM

Post #12 of 14 (113 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

Missed that. I didn't scroll right.

Are you blowing the PCMB fuse or the PCM1 fuse?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Hammer Time
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Apr 28, 2018, 4:39 PM

Post #13 of 14 (111 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

OK, never mind. I see the PCMB fuse is the only one that is 20A.

That directly powers the the fuel pump through the relay and also through the oil pressure switch.

The first thing I would do is unplug the oil pressure switch and drive it around without it. I have seen those things short out the fuel pump feed during oil pressure build up.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Lindsayw790
Novice

May 1, 2018, 4:10 PM

Post #14 of 14 (74 views)
Re: 2003 GMC Sierra blowing pcm fuse Sign In

Ok I will try that thanks for the ideas






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