The infamous check engine light started to come on on my 1994 B4000 Mazda 4x4 4.0L V6 Manual truck about four years ago. My truck seemed to be running fine, so I simply ignored it. It wasn't until I moved to a town where it was required that I get an emissions test done that I discovered I couldn't pass the test when my check engine light was on. I brought my truck to an auto shop to have my computer plugged in to figure out what was wrong. My camshaft sensor was to blame, and the mechanic found a shop with a replacement part for $400. As a poor college student, such an expense was out of my league at the time, so I figured I'd take my chances and hope no one caught me driving around without an I/M sticker on my windshield.

A couple friends of mine had their cam sensors replaced before, but they said it only cost them $50 or so for a new sensor and they said that their gas mileage even went up by like 4 miles/gallon after fixing it. One of the guys said his engine actually wouldn't even start with the broken sensor. I started to wonder whether the dealer I had inspect my truck's computer was trying to screw me, since my part was supposed to cost $400.

A little bit of net searching led me to discover that the sensor my friends may have had to replace were actually crankshaft sensors, which for my model of truck does indeed cost around $50. But then I found camshaft sensors, which really did cost around $400 for a replacement.

My net searches seemed to infer that crankshaft and cam sensors were interchangeable terms. Indeed, they're not. They're different things. But I'm confused as to what a camshaft sensor even does? How is it different from the crankshaft sensor? My truck seems to be running just fine without it working.

I'm also wondering if I might get improved gas millage if I replaced my camshaft sensor. With the soaring cost of gas these days, I'm wondering if that $400 will eventually pay for itself in gas savings. At the moment, my truck averages 21 miles/gallon on the highway (I've measured this by dividing my odometer mileage by the amount of gas in gallons it takes to refuel my tank). I'm not sure if that's good or bad mileage for my particular make and model.

Another question: where is the camshaft sensor located on my engine? My Chilton Repair Manual doesn't provide a very good description of where it's at.

 

your answer to you confusion is that the camshaft sensor picks up the position of the camshaft and the crankshaft sensor does the same for the crank shaft, if your not sure which is which the camshaft is in the head and open and close the intake and exhaust valvesand the crankshaft is what move the pistons up and down.

yes your engine can still run with either on not working properly your computer will just retard (back up the timing) the engine in order to keep running but don't kid yourself it won't last forever and you eventually won't be able to start your truck,

also if you do replace your camshaft sensor you will indeed pickup milage because your enging will running with the proper timing and run more efficently.

this 400 for a new sensor sounds offly expensive, i sejust that you look into the aftermarket and not the dealers since they are crooks on sensors sometimes almost double, i find that napa is resonable priced on thier sensors and no i do not work for napa i just get treated well there

as for your last qustion on a overhead valve engine they are usually located one end of the engine block look for a wiring harness there .

 

I talked to a guy who does diagnostics tests at a shop today. I told him about my visit at the mechanics shop a couple years ago and about the cam sensor that was to blame. I asked him if fixing it might give me better gas mileage, and if it was even worth replacing at all. He basically said it wasn't really worth replacing. The only thing the cam sensor is any good for is it helps at start up, so you can get the best kick out of your crank. But after that, the sensor really doesn't aid in the timing, the crank sensor takes care of that.