Thank you for your extensive reply. But since I don't want to mess things up and render the vehicle inoperable, I'd like to ask a few clarifying questions. <P>If I understand you correctly, I should set "Clear all codes" and then "Level" under each of the following: ECM, BCM, IPC and CRT. (By the way, are these acronyms for something, or random code letters?) <P>During the next run the computer will set new codes. I should then check them again and compare the codes to the ones I'd written down during the first step.<P>If I understood you right, these codes should change each time, and if they are consistently reset, the issue must be addressed. Should this happen, how is it "addressed"? <P>On the other and, if the new codes set are different and the "Service Engine Soon" alert comes on, I can presume everything to be all right and no further action is required - right?<P>Again, thanks for your assistance.