PCMs may need to be reprogrammed for several reasons. One is to fix factory bugs. Every time Bill Gates rushes yet another version of Windows to market to perpetuate the Microsoft revenue stream, it always turns out to have bugs and security holes that were somehow missed but must be fixed by downloading and installing the latest Windows “service pack.” It’s a never-ending cycle of upgrades and patches. Fortunately, it is not that bad yet with automotive PCMs, but it has become a crutch for automakers who rush products to market that aren’t quite ready. This philosophy of “build it now and fix it later” creates a lot of unnecessary recalls, but at least it gives technicians a way to fix factory mistakes without having to replace any parts.
A reflash may also be required if the factory settings for the OBD II self-diagnostics turn out to be overly sensitive – especially after a few years of operation. The same goes for driveability. What works fine in a brand new car many not work so great after 50,000 or 100,000 miles of real-world driving. Changing the fuel enrichment curve, spark timing or some emissions control function slightly may be necessary to eliminate a hesitation, spark knock or other condition that develops over time.