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HP Tuners - learned the hard way about how sensitive the truck is when programming

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24K views 23 replies 11 participants last post by  RDF1  
#1 Ā· (Edited by Moderator)
So...I learned a lesson that will annoy me but I thought I would share with others, in case anyone else ever decides to program their truck.

It's a 2003 GMT800 P59 PCM. Stock. I was looking to adjust very minor things such as knock sensor sensitivity, gear change because of a slightly non-stock tire size so my gauge is more accurate, and to adjust idle up 100RPM. Nothing dramatic.

It turns out that if you have an aftermarket radio in your vehicle of this year, you need to remove both the Radio fuses before reading and writing anything to the PCM. Why? Because with an aftermarket radio you also have an aftermarket chime. While you are writing, it makes the car chime, that chiming causes just enough of a voltage drop to the write up, and it bricks the PCM. You also can't leave the door open for the same reason.

What annoys me is that this apparently is well known to HP Tuners, as soon as I called in to ask why my write stopped, he asked about the stereo, first question. And that's when he told me it's a common problem. I asked why they didn't have that in their docs, they said simply buyer's problem. So, now I am ordering a new PCM and a harness to program going forward on my workbench. And I have to buy another license from HPTuners since it's a new PCM ID

Thought I would post this here just in case anyone else ever programs these and was not aware.

(I'm extra annoyed as I have been programming cars since the 90's, I've done dozens and never bricked a PCM before now)

I'm going to try to see if I can unbrick the PCM once I have the harness, but I need my truck running, so another PCM is needed right away to get back on the road.
 
Discussion starter · #8 ·
Yes, I have a copy of the original stock PCM saved. And, yes, that's why I am getting a bench harness, to see if I can save the PCM. I'm hopefull, but figure if I have the replacement as well, at least the truck will move :)

Like a I said, lesson learned. I've been programming same year corvette about a dozen new writes over the last year and never had to do that before (also has aftermarket stereo). But now I know. And it gave me an excuse for a bench harness purchase :)

Battery was fully charged and is only a month old, that part I've encountered before so I knew to have it on the charger and did the new battery for extra insurance, didn't matter.

These years just seem a little delicate, I'll be more careful on any car in the future.

And this was just for others to find, maybe this helps someone in the future. I do feel HP Tuners should add a little bit of a disclaimer somewhere there that says to be extra careful and pull fuses for anything in a vehicle, it's not hard to add to the docs near the beginning.

Anyway, thanks for the chat :)
 
Discussion starter · #17 ·
Well, I swapped in a replacement ECM and went through learning 30 min to get it running again. So that's good.

I also found some pieces to get the bench harness started and attempt to save the original. Would be nice so I don't have to buy 2 credits, and I can keep this ECM as an extra in case I brick it again :)
 
Discussion starter · #19 ·
Just as a FYI, I was able to take the old P59, put it on the bench harness, short the ground, and was able to reload a stock program into it. I checked it for a bit, and it seemed to be good again.

I then loaded back in my modified code, it liked that as well. So, threw it back in the truck and it runs fine.

So, it's a good trick to know to reflash a bricked ECM.
 
Discussion starter · #20 ·
Also, just in case anyone is interested in the harness and building one cheaply and quickly, I found this one on Amazon:


The only thing wrong with it is the power supply is too low on the amps. It's only 2amps, and I think that's too weak, it's close but I wanted some room. So I also bought this:


It's a 5amp draw

I also wanted a on/off button, so I lastly bought this:


I then threw away the weak power supply, swapped in the new one, soldered it and the on/off switch together, taped it up a bit, tied in a separate ground wire from the pin4 port to use to ground the PCM for reset and it worked great. For under $50, I now have a good enough setup for a hobbyist and the occasional use.

I'd highly recommend this. It's not high grade, but very easy to get together and solid enough to work consistently.
 
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