Is there a way to tell what year truck my ECU came from? I have a feeling it is not the original unit. When I pull the diagnostic codes I get the codes from a later model such as 52 for the knock sensor or 21 for oxygen, but my truck is an 85. I have the 85 sevice manual and the codes the manual specifies dont go above 20 or so. I am thinking I got a later model ECU in the truck and want to see if there is a way to verify this.

On a side note, would having the wrong ECU cause it to throw codes? reason is, my oxygen sensor is brand new and I assume its working since i just passed emmissions, but I still get the code 21. Dont later models have a heated sensor?