Camshaft and Crankshaft Position Indicators

A couple months ago the Check Engine light on my 1991 Buick LeSabre came on. I took the car to my trusty mechanic and was told that the camshaft position sensor was bad and for about $150 it could be fixed. About an hour later he called me and said it was not the sensor but was a magnet mounted on the timing chain that had disintegrated and would cost about $550 to replace. He added that it was no big deal and the car would run okay without the camshaft position sensor working and since my car was on its last legs anyway to forget it. He also said there is a crankshaft position sensor that will do the job.

My question is: Why does the car have both indicators? Since the data provided is a pulse indicating shaft position, the position data should be identical. Could GM actually have implemented a back up system in case of failure of one indicator?

The car seems to run okay except it does stall now and then on startup.

The crankshaft position sensor signals the computer for ignition timing. The camshaft position sensor determines the injector pulse width on the power stroke of the #1 cylinder. If the camshaft sensor signal is lost, the computer will go to a default injector pulse width to keep the engine operating. This default injector pulse width is usually on the rich side.


Now I ask you; where else can you get an answer like that? Wow!

Tester, you are amazing!

Tester, you have put my mind at ease, many thanks. And I second the comment by mcparadise “Tester, you are amazing!”