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Steve
Steve, Service Manager
Category: Chevy
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Experience:  25+ Years experience as a professional working automotive technician; ASE L1 master technician
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I have a 2000 Chevy Blazer that I just purchased a new ECM ...

Customer Question

I have a 2000 Chevy Blazer that I just purchased a new ECM for. When it was put on the vehicle it still didn''t start. Thinking the part was bad I went back to the parts store. They told me that there is a procedure that takes about 20 minutes for the vehicle to learn operating system. While talking to a mechanic at a garage he said there should have been a print out given with the ECM. Needless to say the parts store doesn''t have access to it. Any idea where I can find out the sequence of events that needs to be done after the module is re-installed? Thanks!
Submitted: 6 years ago.
Category: Chevy
Expert:  Joe replied 6 years ago.

Hello lfish, Starting in the year 1996, all GM vehicles are equiped with OBD2 compliant ECM's. When replacing the ecm in a 96 or newer GM vehicle, the new ecm has to be "flashed" or programed for the particular vehicle. Unfortunatly this is not a diy friendly thing. The vehicle has to be connected to a flash tool/scanner that only the dealers and a very few independent shops have. Without flashing the new ecm, the vehicle will not start.

What is the reason you replaced the ecm in the first place?

Customer: replied 6 years ago.
The ECM has already been flashed. I'm just looking for the sequence of things that have to be done in order to get the vehicle to start. I've been told you have to turn on the key for x amount of minutes then shut it off, then crank it then shut it off. I just need to know what to do for how long at a time. Thanks.
Lynn
Expert:  Joe replied 6 years ago.
There is no sequence of events. It should start right up if it has been flashed. Why did you replace the ecm in the first place? Is there a theft light or secutity light flashing on the dash? Did the car run before the ecm was replaced?
Customer: replied 6 years ago.
The mechanic at the garage I stopped by to ask about this is the one that mentioned that there is a procedure to follow. He said I should have gotten a print out with the ECM. The guy at the parts store told me the same thing but he doesn't have access to the print out. The vehicle ran fine before it went out. When it was put onto another vehicle it did the same thing it did in the Blazer. Wouldn't start and was really rough sounding when it was tried. My local mechanic is the one that diagnosed it. Thanks.
Expert:  Steve replied 6 years ago.

Hello!

There are two things that must be done when a new PCM is installed.

(1) It must be programmed with the exact software calibration for your vehicle. This requires a scan tool with programming capability and a subscription to GM's corporate technical database to obtain the software to install. You state that the PCM has already come programmed; if the PCM is not programmed with the correct software what you will experience is that the vehicle will just crank and make no attempt to start. You have stated that the PCM has already been programmed before you installed it, so for the moment lets assume that it contains the correct software calibration. If the procedure I have provided below does not allow the vehicle to start, then there is a good possibility that the software included when you purchased the PCM may not be the correct calibration for your particular vehicle. If this is the case, you will need to have the vehicle towed to a GM dealer or an indepenent shop with programming capability to have it configured.

(2) Your Blazer has a factory security system called "passlock". The PCM is one of the modules involved in the passlock system, so when the PCM is replaced it must be programmed to recognize the other passlock components in the vehicle. I believe this is what the other person you talked to was trying to describe. using a GM scan tool, the passlock system can be programmed in about 5 minutes. If you do not have access to a GM factory scan tool, there is a manual programming sequence for the passlock system to allow the vehicle to relearn the security information. If the passlock system is what is preventing the vehicle from starting, it will crank over but there will be a "security" indicator lit or flashing on the instrument panel.

The manual passlock programming sequence takes at least 30 minutes to complete. Here is the procedure:

  • Turn ON the ignition, with the engine OFF.
  • Attempt to start the engine, then release the key to ON (vehicle will not start).
  • Observe the SECURITY indicator on the dash, after approximately 10 minutes the telltale will turn OFF.
  • Turn OFF the ignition, and wait 5 seconds .
  • Repeat this sequence two more times for a total of 3 cycles/30 minutes (the vehicle is now ready to relearn the PASSLOCK(TM) Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK). IMPORTANT: The vehicle learns the PASSLOCK(TM) Sensor Data Code and/or password XXXXX the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.
  • Start the engine (the vehicle has now learned the PASSLOCK(TM) Sensor Data Code and/or password).
  • Steve, Service Manager
    Category: Chevy
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    Experience: 25+ Years experience as a professional working automotive technician; ASE L1 master technician
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