2006 Suzuki Forenza Trouble Code P0516

The check engine light on my Suzuki Forenza is on and it will not turn off. I was told it was due to a P0516 OBD II trouble code. The smog tech said it had to do with the crankshaft sensor. I'm told this is nearly impossible to replace and will cost a lot. My Forenza only has 70,000 miles but was not maintained at all. i ant to fix the problem, get the car to pass the smog check and return it to running condition. Another family member will be using it since it's paid off already. The person who I let drive the car during the time I owned it has a tendency not to be truthful so I can't really trust that they in fact had a mechanic do a real diagnosis. I would like your opinion before moving forward with repairs. I can't find the smog check he did that failed, if he even in fact did a smog check at all.. The only paperwork I can find by a real mechanic states that trouble code P0516 was found in the computer system. They supposedly checked both the crankshaft sensor and camshaft sensor and found that both were functioning properly. The car is driving. I need to know what to do. Please help. Thank you.