This is pretty old but is from Garmin support:
Is my Garmin nuvi compatible with WAAS/EGNOS?
12/17/2010

If you have a Garmin nuvi 300 or 600 series device you will have the option to enable WAAS/EGNOS. Enabling WAAS/EGNOS on your nuvi 300 or 600 series unit may improve the accuracy to less than three meters on average.

To enable WAAS/EGNOS on your nuvi:
1.Power the nuvi on

2.Touch on the Spanner/Wrench icon from the main menu screen

3.Touch System

4.Touch Off next to WAAS/EGNOS

5.Touch On

6.Touch OK


WAAS/EGNOS will now be enabled on your device.


Note: Only the nuvi 300 and 600 series have the WAAS feature. All other nuvi models contain a high-sensitive GPS receiver that does not require the WAAS feature.

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