Y61 2002 GU Sub tank fails self test

OK, I'm running out of ideas. I think I have read every forum post about this issue but it still has me stumped.

Like many others, the sub-tank light is permanently on and the pump is not working. So these are the steps I've taken so far:

1. Disconnected battery for 30mins to reset ST ECU. I have also done this after each of the following steps.
2. Disconnected both terminals of the second battery.
3. Installed heavy duty earth straps from body to chassis and from engine to chassis, filing contact surfaces.
4. Jury rigged the pump to confirm that it works.
5. Drained the sub tank to half full. The main tank is on quarter full.

I do not have cruise control.

After each of these steps I reconnect the battery and restart the engine. After a minute or so the sub tank light comes back on and stays on.

Any new ideas?

I have not yet looked inside the sub tank.

I dont really want to bypass the ST ECU but in the absence of any new ideas I think it has come to that.

Hope you can help.

N.

While the sub tank warning light is on the dash, have you tried the self diagnosis procedure to determine the error code?

With my 2004 GU to enter the self diagnosis procedure (while the warning light hasn't been cleared) car is off, then start the car and turn the sub fuel tank switch ON and OFF 5 times within 3 seconds.
The light on the switch will blink the error code.
One long blink and then a series of short blinks. http://cloud.tapatalk.com/s/63c936e3...nual_Pages.pdf