When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
i wouldn't say you would have to 100% get a tune but you certainly wouldn't be taking full advantage of the downpipe. so a tune is extremely recommened yes
If you don't want to do the tune, but you don't want the CEL then there is always the 90* elbow between the o2 sensor and the threaded hole in the exhaust pipe for the sensor.