The "implausible signal" code is very different - don't confuse the two. If you get the code saying something about the signal being implausible, that doesn't mean the sensor is bad - it just means the signal being sent from the sensor the ECU is not what the ECU expected. This is nearly always due to the timing belt and/or distributor being installed incorrectly. If the valve timing in relation to the distributor/intermediate shaft position is off by even a tiny bit, the ECU will throw this "implausible signal" code for the camshaft position sensor. In theory, I suppose this could also be caused by a wiring problem from the sensor to the ECU... but I haven't heard of that happening yet.
The camshaft position sensor is just a hall sender - it either works or it's completely broken. There is no in-between.
If, on the other hand, you are getting the "open or short to B+" message, that is a good indication that either the sensor is bad, or the plug is disconnected from the sensor, or the wiring from the sensor to the ECU is damaged (broken and/or shorted).
Override, bust out your Bentley manual to find the pins on the ECU that correspond to the input from the camshaft position sensor, then use a multimeter to test for continuity between those contacts in the large ECU connector/loom, and the contacts at the connector for the camshaft position sensor. If the continuity checks out, then you'll most likely need a new sensor (replacing just the sensor is possible, but you have to take your distributor apart to do it).
izzo, make sure your timing is dead nutz. Look at the Bentley procedure for illustrations, but pay careful attention not to confuse their instructions for the Canadian (1.8L) engine with yours (ABA 2.0). With the belt still on the vehicle, turn the crankshaft until the mark on the camshaft pulley lines up exactly with the arrow/mark on the plastic cover between the cylinder head and the camshaft pulley. Now remove the plastic timing plug from the transmission bellhousing and you should see the "0" mark on the flywheel line up with the pointer in the bellhousing. Now (and this is the really important part), remove your distributor cap and make sure that the metal contact on the rotor is pointing exactly to the mark on the distributor body (should be very near where the #1 plug wire would be if the distributor cap were on). The "mark" can be tough to find - especially if you have that plastic cover on below the rotor. If any of that stuff isn't perfectly in place, then correct it.
ABA timing gets done incorrectly so often. It can be tricky even for those of us that have been doing it for a long time.