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S54 Crankshaft Sensor Testing
 
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Pelican Technical Article:

S54 Crankshaft Sensor Testing

Nick Czerula

Time:

2 hours2 hrs

Tab:

$130

Talent:

***

Tools:

Set of sockets, 5mm Allen bit, flathead screwdriver, DVOM

Applicable Models:

BMW E46 M3 Coupe/Conv (2001-06)
BMW Z4 Coupe/Conv (2006-08)

Parts Required:

Crankshaft position sensor, sealing O-ring, crankshaft sensor fastener

Hot Tip:

Work with a cool engine

Performance Gain:

Car will start and run well

Complementary Modification:

Repair oil leak from faulty crankshaft sensor sealing O-ring

The digital motor electronics (DME) engine management systems in BMW Z4 vehicles uses the engine control module (ECM) to control fuel injection, ignition and other important drivetrain functions. The ECM sequentially triggers the fuel injectors to spray fuel into the intake ports and then, a split-second later, triggers the ignition coils to fire the spark plugs. This sequence of events is timed by using the crankshaft position. Using the signal from the crankshaft sensor, the ECM "knows" which cylinder is ready for fuel intake and then, later, for ignition.

The crankshaft position sensor is located near (below) the starter motor, mounted in the engine block (crankcase). The sensor reads a toothed reluctor wheel mounted to the end of the crankshaft. It then sends a signal to the DME used to identify cylinder location. If this signal is missing, for example from a faulty crankshaft sensor, then the engine will not start. You can consider the signal from the crankshaft sensor the RPM signal for the DME.

BMW Z4M models use an inductive style sensor. The crankshaft sensor is constructed of a permanent magnet with a coil around it. The magnetic field strength changes when a toothed wheel passes through the magnetic field of the magnet. This changing of the magnetic field induces a voltage in the coil. This voltage is what is used by the DME to determine engine positon and speed. In this article, I'll go over the steps involved with testing the crankshaft position sensor on BMW Z4M models. Other models are different as they use a Hall-Effect style sensor. I will show you a few different ways to go about this.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.

Vehicle models change and evolve as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

The crankshaft position sensor (red arrow) is located near (below) the starter motor (yellow arrow), mounted in the engine block (crankcase).
Figure 1

The crankshaft position sensor (red arrow) is located near (below) the starter motor (yellow arrow), mounted in the engine block (crankcase).

Remove the intake air housing and ducts.
Figure 2

Remove the intake air housing and ducts. See our tech article on intake air housing removing.

The electrical connector is located under the center of the intake manifold, you can just see it from above.
Figure 3

The electrical connector is located under the center of the intake manifold, you can just see it from above. Working behind the starter motor (yellow arrow) at the left side of the engine, disconnect the crankshaft sensor electrical connector (red arrow) by pressing the wire retainer and pulling the male connector end out. The inset shows the connector unplugged.

Once disconnected, you will have to peel the boot back at the sensor side of the harness, then insert a back probe and plug the sensor back in to test the DME side of the circuit.
Figure 4

Once disconnected, you will have to peel the boot back at the sensor side of the harness, then insert a back probe and plug the sensor back in to test the DME side of the circuit. Red arrow points to terminal 1, the sensor ground, 0 volts DC on the DME side when sensor is disconnected, 2.5 volts DC when plugged in backprobing. Yellow arrow points to terminal 3, sensor signal (also has the sensor circuit integrity voltage), 5 volts DC on the DME side when sensor is disconnected, 2.5 volts DC when plugged in backprobing. Blue arrow points to terminal 3, shielded ground wire, zero volts.

With the sensor plugged in and backprobing the connector (red arrow), terminal 1 or 2 will be about 2.
Figure 5

With the sensor plugged in and backprobing the connector (red arrow), terminal 1 or 2 will be about 2.5 volts DC.

Next, connect two jumper wires with insulated spade terminals to the crankshaft position sensor terminals (red arrows).
Figure 6

Next, connect two jumper wires with insulated spade terminals to the crankshaft position sensor terminals (red arrows). Then connect you DVOM to the jumper wires and turn it to AC Volts. Should read zero volts engine still.

Crank the engine over, the sensor should produce about 0.
Figure 7

Crank the engine over, the sensor should produce about 0.5 volts A/C when cranking.

With the sensor removed, plug the electrical connector back into the sensor.
Figure 8

With the sensor removed, plug the electrical connector back into the sensor. Then connect a Mercedes-Benz scan tool, turn the key to run but leave the engine off. Navigate to engine data that displays engine RPM. Use a large wrench and move it toward and away from the tip of the crankshaft sensor, avoiding contact but coming close. Move the wrench quickly, you will feel the magnetic field. As you move it, the scan tool RPM parameter should go from 0 RPM when wrench is static to an RPM reading of 20 up to 1500 RPM (red arrow) depending on how well you break the magnetic field. You can also test using a Mercedes-Benz scan tool with the sensor installed or removed. Installed, cranking ROM should be about 300 RPM or actual cranking RPM (depending on battery voltage).

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Page last updated: Wed 12/7/2016 03:06:24 AM