This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series. The book contains 272 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any 3 Series owner's collection. The book was released in August 2006, and is available for ordering now. See The Official Book Website for more details.
The crankshaft position sensor is very important to proper engine operation. If it fails or works intermittently, the engine will either barely run or not start at all. Fortunately, the engine's main computer (DME) will indicate whether or not there are problems with the crankshaft position sensor. (See Project 28 for more details on reading fuel injection error codes.)
The sensor itself is easy to reach and replace. On some models, however, the wire harness that connects the sensor to the rest of the car is hidden underneath the intake manifold. Remove the intake manifold to replace the sensor. Or, you may be able to access it by reaching underneath the manifold--if you have skinny arms--and removing the oil filter housing first. Either way, getting to the harness connector is not easy.
To replace the sensor, unscrew the 5-millimeter Allen bolt that attaches the sensor to the engine case. The sensor will always be mounted facing the toothed degree wheel attached to the front of the crankshaft. Depending upon which car you have, you may need to remove the radiator fan (see our radiator replacement article).
Wire harness routing varies widely from car to car. On the E36 six-cylinder models, the harness is routed through a plastic cover and then underneath the intake manifold. Disconnect the wire harness from the engine, and replace the sensor. Be sure to route the new harness along the same path as the old harness.
On some E30 cars (1984-1987) 325e/s models, there are two sensors that read the toothed crankshaft wheel. When replacing these, double-check that you don't accidentally switch the two sensor plugs. They should be color-coded to match their receptacle plugs.
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The crankshaft position sensor (orange arrow) is relatively easy to get to. However, like the camshaft position sensor, the wire harness connection is hidden underneath the intake manifold. Remove the intake manifold to replace the sensor; or, if you have skinny arms, you may be able to reach in there if you remove the oil filter housing first. The wire harness is integrated into an upper plastic guide (green arrow). The wire disappears beneath the VANOS solenoid and the intake manifold (blue arrow).