Various boarders report that when their ETS failed, they were doing stuff like driving on the highway. Their cars quit with no appreciable warning. Do you want to be doing that with a semi following close behind?

The ETS light is a sign that you need a new ETS. Try and get yourself a good price, but get it fixed before it dies. I don't want to be behind you when it fails catastrophically.

Also, log onto the NHTSA website and report it. If there are enough reports, maybe NHTSA will force Volvo to recall the part (although it sounds like they don't have a better alternative). At least they would be forced to pay for the replacements.

Volvo should be ashamed of themselves for this very dangerous failure.