Check-engine on now

[vectorg]

hello,

First post here, but I've been using a fuel-efficient driving style for many years.

Here's my question: my check-engine light just came on yesterday and I was wondering if this is a good time for me to buy a ScanGauge? What are the chances it will save me some money just to see why my check-engine light is on?

Last time the light came on it was an air-sensor that needed to be replaced for about $400.

Thanks.

1999 Camry 4-cylinder auto