If a reader/scanner is capable of clearing codes under any condition, it will clear codes engine running or not. Given the opportunity, I will almost always check/clear during the same run session, then try to repeat the conditions before a restart. Some diagnostics only run during a cold start (such as a glow cycle), and/or after a specific number of starts or warming cycles. A high class code in history, even if erroneous, can override clearing the code, and relight the SES. P0700 won't do this, so if it returns, the TCM is still seeing the condition that set it and requests the code and SES. If P0700 is that persistent, there must be an underlying code. You need a bidirectional scanner to clear codes from history, so they should be there. Anyone with a smog inspection in the near future should be careful of this. Clearing history will also reset ALL the smog diagnostics, and restart them from the beginning. It can take days or weeks to get them all to clear. Learned that the hard way.