Air Pump Won't Shut Off

[Kestas]

Unfortunately, Arthur Dalton and I were in the middle of diagnosing my problem with the air pump running continuously when my thread got lost in the server crash.

To recap, the air pump on my 95 E320 runs continuously. Per Arthur Dalton's advice, I learned that my car does not have a switchover relay in the relay compartment. The codes I got were:

5, 19, 21 (on-board diagnostic module)
13, 49 (Pin 8)

Arthur last wrote:
Unplug the pump and run the car a couple of days to
see which codes
clear by themself. specially the 02 code
Also, check that the purge valve is beating [Search]
How is harness?????????

Engine wiring harness was replaced two years ago.

I found the purge valve was plugged with granules (activated charcoal?). I cleaned it out and got it working with 12v and some tapping, then gave it some exercise with 12v and WD-40. Now it has a healthy heartbeat. But the air pump still runs.

After running the car with the pump unplugged I got only Code 13 (Pin 8). With the pump connected I get the same code, which is the only code I get after reading/clearing codes a few times. So now I'm looking at Code 13 as the clue to the problem.

Additional info: O2 sensor was replaced two weeks ago