2000 Volvo S40 wont start

Here's the problem:

"My mechanic put a code reader on the engine to analyze it and it showed that the camshaft position sensor was the problem".

Diagnostic fault codes never say to replace parts or that one is defective. They only indicate the circuit or system that needs further diagnosis. When a sensor is referenced in a fault code, that sensor is actually responsible for the code about half of the time. The mechanic's first step in diagnosing the cause of the code is to inspect the wiring and connectors.

Also, there are a number of fault codes related to the camshaft position sensor and they mean very different things. I need to know the exact code number or its description.

Everything you've described suggests the timing belt has jumped a few teeth. The camshaft position sensor's signal will be out-of-sync with the crankshaft position sensor's signal, and that might set a fault code. I'm guessing you have a 1.9L engine. If so, that is an "interference" engine, meaning with a jumped timing belt, the open valves will be hit and bent by the pistons. Simply replacing the timing belt won't get the engine running again, at least not very well. The bent valves will need to be replaced first.

The only cars I have memorized are Chrysler products. On those, if the timing belt jumps one tooth, power is greatly reduced, the Check Engine light turns on and the fault code is "cam and crank sync". At two teeth off, the computer will shut the engine down to protect it. At three teeth off, or when the belt breaks, open valves are hit by the pistons as they coast to a stop. Very few people report hearing any unusual noises. The typical symptom is the engine lost power or it simply stopped running.

At the mileage you listed, the timing belt should have been replaced at least once already as a maintenance item. All manufacturers have their own mileage recommendations, but in the case of older Hondas, they used to recommend every 75,000 miles, ... And their belts typically broke at around 65,000 miles, resulting in a lot of unhappy owners. Very few manufacturers specify a replacement interval longer than 100,000 miles. If your engine has an upper cover that's easy to remove, pop that off and look at the teeth on the belt. If any are missing, or the sides of the belt are chewed up, it's time for a replacement. It is customary to replace any tensioning devices and idler pulleys to insure the quality of the repair, and if the timing belt runs the water pump, every conscientious mechanic will insist on replacing the pump too. Failed water pumps cause a lot of timing belt failures so it's silly to not replace it while you're in there.

Incorrect timing alone will make the engine very hard to start, but to know for sure, you can either remove all the covers to check the timing marks, or you can do a compression test, then a cylinder leakage test. If a compression test shows real low compression, suspect bent valves, but if compression readings are somewhat normal, that is not conclusive. With a timing belt jumped one or two teeth, compression could still be fairly normal.

A cylinder leakage test involves pumping compressed air into a cylinder when that piston is at top dead center on the compression stroke, then reading the percent of leakage. While a compression tester uses a hose from the spark plug hole with a check valve in it, the hose for the cylinder leakage tester has no check valve. Compressed air goes through the tester, then into the cylinder. Anything over about ten percent leakage is cause for concern, but the nice part is you can locate the cause of that leakage. Listen for hissing at the tail pipe. That indicates a leaking exhaust valve. A leaking intake valve will cause hissing at the throttle body. Leakage past the piston rings will be heard at the oil fill cap or dip stick tube. A leaking cylinder head gasket, (or cracked cylinder head), will cause bubbles in the radiator.

If cylinder leakage is real low for one cylinder, it is going to be low for all of them, and you can expect to find no bent valves. The timing belt still could be off a few teeth though, and you'd have to dig deeper to look at the timing marks to know for sure. It's pretty common to find a section of teeth missing from the belt, and continuing trying to start the engine can cause the belt to jump more teeth which leads to bent valves.