Interesting. When the PCM is flashed, only vehicle specific data for the options on the vehicle are included. Not sure what the technical name is for that type of file, but it remains there indefinitely even if power is removed. With older PCM's, the vehicle specific data was stored in a PROM, (Programable Read Only Memory). If/when the PCM was replaced, the original PROM was transferred to the new PCM.

 

With the older ones, transferring it (if it isn't bad) would make sense since PROM is write once and it isn't soldered to the board. I guess GM wants people dependent on dealerships, which is why you need their scan tool to reflash the newer PCMs when on the older ones, making the new one work properly is as simple as moving a PROM module.

 

The used replacement ECM I am using is from a 1999 S10 Blazer matching SERV: 16263494 numbers. That is the same required number that all parts stores ask you for when they are looking up their $89 to $339 reman ECM units.

Excellent information about the ECM and really good news pulling out the orig factory ECM won't kill it. I have the new (used) ECM in the Blazer, Monday the Flash guru will be coming to the house to load the latest software and my vehicle options into the module. Keeping my fingers crossed.

 

Please post the results.

 

Got the used ECM flashed with the Blazers VIN, options and security learn, went on a test drive the the P0758 issue is now FIXED. The ECM was the culprit.

Just to summarize,

My daughter got the P0758 code (Shift Solenoid B electrical fault).

The Truck went into limp mode (3rd gear only).

Using my scanner I cleared the code and truck would shift 1st to 2nd, 2nd to 3rd, then the P0758 would pop up and go back into limp mode every time.

Took the Blazer to shop and had them test:
- Shift Solenoids - All tested good (volts and ohms, and scan tool toggle)
- Trans wiring harness - all wires tested good
- ECM harness to trans harness - all wires tested good
- Advised to buy replacement ECM and have flashed
- Found matching SERV # ECM from 1999 S10 salvage truck
- Removed factory ECM from my Blazer, installed used ECM from S10 truck
- Had local tech flash the used ECM with my VIN and truck options
- The Local Tech loaded the security setting into the ECM
- Took the Blazer for a test drive, no more P0758 code, no more limp mode

This was my unique problem and it may not be a fix any other vehicle, but then again it may. You should have everything else checked listed above before you change the ECM. You will HAVE to get any replacement ECM programmed with your VIN and options and learn the vehicles security before the replacement ECM will work. Until it's flashed and set up correctly your vehicle will not run. There is NO DROP AND SWAP ECM's for this type of vehicle.

It's pretty funky how the Flash technician had to set the parking brake, bring the engine to the correct temp, floor the accelerator then punch in the security learn. He knew what he was doing and I was glad we have a person who will come to my home to do all of this. Please don't bitch at these folks because they charge $100 bucks to do this, he has thousands if dollars invested in the flashing units and annual licencing fees he has to pay to be current with all of the auto manufactures software changes.

I just glad to have the old Blazer back on the road, thanks for all of the input to this issue from the forum members, for some reason I feel I'll probably be back with a new issue, you gotta love there old cars and trucks...

 

Thanks for posting back, glad the problem is solved.

THANK YOU! Most people don't realize the amount of money that techs have to spend, (most times out of their own pocket) on tools, test equipment & training. They need a return on their investment, and at $100 a pop, it takes a mighty long time to get the return