The check engine light on my 500 SL triggered. I checked the codes with car soft and got a "O2 sensor heater circuit" In all the programs I have access to I have not found any information on that circuit operation or how to check it. I cancelled that code and it has not returned. It has since thrown codes for steering high pressure cut off, ABS system feed, ASR system feed and the last code was last night code 6 pin 7 which according to the code chart is not applicable to U.S. vehicles. to date none of these codes have returned but pin 19 has had a consistent code 4 air injection system faulty and code 5 egr system faulty. These codes will not cancel for some reason but do not seem to be triggering the light, every time that the light has triggered there has been at least one other code. The clutch on the air pump is working and the pump is pumping air. The egr system seems to be functioning properly except that the passage in the intake manifold is plugged, just discovered that this morning and have not had a chance to r&r the manifold to clean it out. Any ideas why these codes will not cancel and why I keep getting these odd ball codes sporadically. Anyone have any ideas?