Secondary air injection pump runs when engine is off

The secondary air injection pump fan on my daughter's 1998 VW Beetle is turning on and off intermittently by itself with the car off (ignition off, keys removed). It will remain on indefinitely at times until it drains the car battery. Currently I need to remove the battery cables when the car is parked to prevent the fan from running and keep the battery charged. There is no check engine light or other warning light coming on.

According to the Haynes repair manual, the air pump fan is controlled by the ECM and is only supposed to run for about a minute after the engine starts up.

This is a 2.0L engine with 5 speed transmission. Service work that has been previously done to the emission system is replacement of a defective mass flow sensor.

Questions I have with this current problem are:

1. What would cause the fan to turn on with the engine off and the ignition off?

2. Is the ECM defective? How would one check this?

3. Would a defective ignition switch keep power on to this pump fan when the ignition is off and the key removed?

Or is there a relay or solenoid that isn't opening or remaining open when de-energized and causing power to remain on to the air pump fan?

I may end up taking this into a dealer to fix but would first appreciate any help and advice to debug and fix this before doing that.

Thanks in advance.

R. Jones
Issaquah WA

sounds like a stuck relay for the secondary air pump. I dont remember off the top of my head where it is, But i think its on the relay pannel under dash. just take out the 3 t20 torx screws and with the car off (when the pump is running) feel arround the relays for the one that is hot or warm.