What do you mean exactly?
Low gear as in first gear. There is probably a 'D' for drive too.
I suggest you read your owners manual, page 235. Here it is in case you don't have one --- file:///C:/Users/tcw/Downloads/2008- Caliber-2nd.pdf
My 2005 Ford focus that had a little button on the shifter that turned the overdrive on and off. With o/d off it only ran the lower gears from first up to third I believe. L is low gear. In other words it's like driving with o/d off. I think it's purpose for getting out of snow.
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