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I need help. Truck would not crank or start.Both batteries tested at 11.3 v. Got new batteries. Still no crank. Was able to jump starter, but still no crank. Took to dealer. They said no power to ecm. Wanted $900 to put in fuse block in engine compartment and then they could run further tests. I bought a fuse block and will put in myself. Question. Utube says I cannot reset truck by tying pos and neg cables together. Is that ok.?
 

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2017 2500HD LTZ Z71 Custom Sport Ed, MW7
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Need some more info here Candace. Truck year would be a good start, any upgrades you have done, etc. Please provide every detail about your truck that you can so we know what your working on.
 

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Need some more info here Candace. Truck year would be a good start, any upgrades you have done, etc. Please provide every detail about your truck that you can so we know what your working on.
Hi. Thanks for responding. It’s an 04 gmc 6.6 duramax LLY. Everything is stock. I have done nothing to it. Except change dead batteries. Is it true that if you don’t exchange batteries post by post you will need a reprogramming?
 

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I don't think you would have to reset anything just by changing batteries, except radio presets, but if your starter doesn't spin when you jump it makes the starter suspect IMO. Providing the batt. cables are good, check your frame ground under the driver battery tray, its on the underside of the front of the truck, might as well check the other one under the driver footwell on the frame as well. I would remove them and make sure of a metal to metal contact. also check the wire loom rub issue at the front driverside innerfenderwell where the loom can get abraded by the inside of the plastic fenderliner. Good luck!
 

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The safest way is to just detach both NEGATIVE cables maybe 20 minutes, or even overnight. Don't let the cable ends touch anything - wrap them up. This will 'reset' some things, not others. But it's easy, and it costs nothing IF YOU DO IT CORRECTLY.
 

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Thanks guys! I have checked the loom issue. I’ll check battery tray grounds. So,after replacing fuse box, do I have to do a reset? Does disconnecting the negative grounds do the same thing as tying each battery’s pos and neg cables together?
 

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Thanks guys! I have checked the loom issue. I’ll check battery tray grounds. So,after replacing fuse box, do I have to do a reset? Does disconnecting the negative grounds do the same thing as tying each battery’s pos and neg cables together?
I think you are referring to touching the vehicles sides cables together without the batteries connected or involved to "drain" the ECU or any remnant power left on the vehicle side. This may work, however, really all you need to do is disconnect them as Ron Nielson has mentioned and this will do the same and is safer in my opinion. All this does is remove any power remaining in the vehicle. This may reset some things as Ron has mentioned, but I am not sure it will yield the results you are looking for. In addition to the recommendations already given, I would check over the fuse block and make sure everything is hooked up correctly and of course test every single fuse in there.

Let us know how it goes.
 

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Discussion Starter · #10 ·
I did.Still wouldn’t start.So I bought 2 new batteries. Old batteries were at the end of their life anyway. The thing I thought was interesting was both old batteries tested at the same volts. ?? I don’t know. I’m just grabbing for straws at this point.
 

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Candace
It is apparent to me that you are not knowledgeable about our diesel trucks nor electrical systems. We all start that way and learn as we go. When you have 2 batteries in your truck, they are tied together and make 1 'bigger' battery and the voltage of each individual batteries will be equal to each other.If left long enough without charging, the voltage in each of them will equalize - the stronger battery being 'pulled down' to the weaker battery. When disconnecting cables in your truck, you need to remember that disconnecting something from one does not disable the electrical system overall - there still may be lots of energy in the other battery. When people talk of touching cables, you have to remember that if one battery is still connected, pos and neg, the electrical system is alive and active and touching the 2 cables from the other battery will cause a dead short and a BIG ONE. It will likely be like an arc welder, possibly explosive.

Took to dealer. They said no power to ecm. Wanted $900 to put in fuse block in engine compartment and then they could run further tests.
You should have found out why there was no power to the ECM. That could have been because there was a fuse or two blown. All power to the ECM goes thru fuses. Saying you need a new fusebox is just too simple of an answer. Maybe the dealer explained that to you, maybe not, but you said nothing of it. Maybe there was a broken wire between the fuses and the ECM. It should have been made clear to you. Most people just want to know what it takes to get their vehicle running and maybe that's what you wanted, but on the forum, we attempt to educate, pass on knowledge gained thru the years to others, so that they have more knowledge.

The dealer likely could have wired around the problem area of the fusebox and run the tests they wanted to run. Maybe they did that, maybe not. I doubt it. That would have been the best way to do the testing. Dealers love to have everything new, sometimes without good reason, so that they can test something else. Sometimes they will have you spend thousands of $$ only to find out that they failed to identify the real problem to start with and failed to do proper testing.It happens all the time.
 

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Discussion Starter · #12 ·
You are correct! This is my first diesel truck and my first truck that has two batteries. But thanks for the explanation, makes perfect sense! Our dealer here is notorious for being less than honest. They told me there was no power from the fuse box to the ECM, so they wanted me to purchase a new fuse box before they continued. I hired one of the best electrical guys to come and check it out.his diagnostic machine read class 2 Data link fault, U1000. He told me to take it to the dealer for reprogramming. He said they were the only ones that could reprogram my ECM. Is that true? Hence, the UTube hard set video.;) Thanks again for your help!
 

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He told me to take it to the dealer for reprogramming. He said they were the only ones that could reprogram my ECM. Is that true?
Not true, in an absolute sense. And you may be paying for something that won't solve your problem.There are independent garages that also do programming. Because all newer cars have lots of computers, more and more garages can do the investigation and programming. Also, those garages almost always have cheaper labor charges. And if you have enough knowledge and a capable laptop, a programming interface with the computer, and pay for the online program access, you could do it yourself. But that costs lots of $$$$. See if your town has a GM specialty garage and see what they can do for you. Or even a diesel garage that works on GM pickups. See if there is a diesel pickup club where you live. They often have people who can help you.

I don't know what your best electrical guy did to check the truck out. If he just did a code read, that's not enough. He may have done a lot more. Can't tell from what you write. And it's really easy to make mistakes when diagnosing.

U100 can be a plethora of problems. See attached. You may not understand all of this. And I seriously doubt that you will be able to solve this problem yourself. A capable scanner, such as a Tech 2, and a scope are almost a requirement to determine what is happening, and that requires professional-level help.
 

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