The computer commands movement of the EGR valve via the EVR(EGR vacuum regulator), and measures the actual valve movement with the EVP(EGR valve position sensor), disabling either or both sets a code. If the complete EGR system is installed and operating correctly, but the EGR valve is blocked at the intake manifold, you won't get a code but the motor will be detonation prone because the computer adds more timing when it commands the EGR to open. This is why it's beneficial to keep this system. The only way you won't get a code and not make the motor ping is by spending $500 on a tuner to shut off the whole EGR routine inside the computer, but that's not terribly cost effective.