I just got my 2010 Ford Escape (a four cylinder) back from the repair shop. It hadn't been starting, and I was told the cause was a broken crankshaft sensor. The repair seems to be successful, and the cost was reasonable. I was curious, though, what is this part and why is it necessary?

— Alice H.

It's great someone figured out the problem and was able to make a successful repair. Crankshaft position sensors are used on all modern vehicles to determine engine speed, crankshaft position and engine speed fluctuations. Speed information is used for many engine management operational decisions. Positioning information is important so that fuel and ignition can occur at just the right time for each cylinder. And fluctuations are studied to determine if misfiring is occurring.

The crankshaft position sensor is the most important of all engine management sensors, and the engine will absolutely not run without it. Determining that a faulty sensor is preventing a vehicle from starting is actually pretty easy, as the engine will not have ignition spark, fuel injector pulses or an rpm reading on the tachometer or a scan tool. Camshaft position sensors also are used, so the management system knows what stroke the crankshaft is in at anytime. Many systems are smart enough to try guessing should this sensor fail and allow the engine to run without it.

In your case, a magnetic crankshaft positioning sensor is used. It's the simplest of several types. It contains a coil of very fine wire and a magnet and is mounted at the front of the engine, adjacent to a toothed pulse wheel. As each iron tooth of the wheel passes near the tip of the sensor, a small electrical pulse is generated. The wheel contains 35 teeth (36 spaces with one missing). This setup results in a signal pulse being sent for every 10 degrees of crankshaft rotation and an indicator (missing pulse) occurring 60 degrees before top dead center for cylinders 1 and 4.

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Problems with a crankshaft position sensor can be complete failure, likely caused by the fine wire breaking, or a more frustrating to diagnose intermittent fault that causes the engine to cut out or sputter. It's tough to say what the cause was for your failure. Heat and vibration likely played a role. Odds are your replacement part should last the remaining life of the Escape.

The gas tank door on my 2011 Hyundai Sonata is making me crazy. Sometimes, it won't open unless I poke and fiddle with it quite a bit. I'm afraid I'll become stranded if I'm not able to buy gas at the right time. Help!

— Gene Parsons

This has an easy fix! Hyundai issued a service campaign bulletin in December 2010 providing instructions for adjustment of the door's actuator and latch spring tension. It's a quick and effective fix if the instructions are carefully followed. This can be done by the dealer or an independent shop with access to the needed service information.