The other day after driving my 2002 S500 (117,000 miles) for 5 miles when I turned off the key the secondary air pump continued to run. It continued to run for approx. 15-20 min after the engine was turned off and ran until I disconnected the pump motor leads. I re-connected the leads and the pump motor remained off. The next time I drove the vehicle to check engine light came on.

It is interesting to me that the pump motor continued to run with the key turned off and removed from the ignition.

Any ideas of what the malfunction may be?