Can I replace with used ECM?

It will still need to be programmed to your vehicle as it will have the wrong VIN in it and the security system will stop it from running. As well as that the ECM will have things like idle speed and timing that need to be synced to your engine. Also on that car you cannot simply unplug the old module, you need to use a scan tool to "remove" the module from the system prior to disconnecting it. Then you replace the module and use the tool again, this time to "Add" the ECM back into the system. Then once it is added in and the security codes and parameters reset you use the scan tool to verify the programming is correct for your vehicle. That means you also need to be connected to GM TIS with the scan tool to do that.

What is the issue with your current ECM? Keep in mind that a yard part will be the same age as yours and could also have problems.

no spark.

no spark 2003 suburban.

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Cheers, Ken