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Crankshaft Position Sensor Testing
 
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Pelican Technical Article:

Crankshaft Position Sensor Testing

Nick Czerula

Time:

2 hours2 hrs

Tab:

$130

Talent:

*****

Tools:

Set of sockets, E8, flathead screwdriver, DVOM, back probes, jumper wires

Applicable Models:

Mercedes-Benz E320 (2003-05)

Parts Required:

Crankshaft position sensor

Hot Tip:

Work with a cool engine

Performance Gain:

Car will start and run well

Complementary Modification:

Replace air filter

A crankshaft position sensor is an electronic device used to monitor the position or rotational speed of the crankshaft. The crankshaft position sensor is used to synchronize engine timing for fuel and ignition control.

The crankshaft position sensor serves the same function as distributors on earlier engines.

The crank sensor is used in conjunction with a camshaft position sensor to monitor the relationship between the pistons and valves in the engine. This method is also used to synchronize a four-stroke engine upon starting, allowing the management system to know when to inject the fuel and into which cylinder. It is also commonly used as the primary source for the measurement of engine speed in revolutions per minute (RPM).

It is located on the left rear of the engine, mounted in the transmission bell housing. The sensor reads a toothed reluctor wheel mounted to the end of the flex-plate or flywheel. 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, the engine will not start. You can consider the signal from the crankshaft sensor the RPM signal for the DME.

Mercedes-Benz 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. I will show you a few different ways to go about this.

Remember, your car may have been serviced before and parts 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. Never work on your vehicle if you feel the task is beyond your ability.

The crankshaft position sensor is located on the left rear of the engine (red arrow), mounted in the transmission bell housing (inset).
Figure 1

The crankshaft position sensor is located on the left rear of the engine (red arrow), mounted in the transmission bell housing (inset). 

Working at the engine cover (red arrow), pull off the two front air duct hoses (green arrows).
Figure 2

Working at the engine cover (red arrow), pull off the two front air duct hoses (green arrows).

To detach the ducts, pull them straight off the engine cover / air filter housing.
Figure 3

To detach the ducts, pull them straight off the engine cover / air filter housing. Then pull the front of the duct out of the radiator support and remove it from the engine. Repeat this step for each duct.

Lift up and remove the front engine cover.
Figure 4

Lift up and remove the front engine cover.

Then, pull the engine cover / air filter housing straight up to remove it.
Figure 5

Then, pull the engine cover / air filter housing straight up to remove it. The cover is held on by four metal clips that grab onto rubber mounts, with the front two shown (red arrows). The rear of the cover has two as well. Once detached, remove the engine cover / air filter housing from the engine.

Working from above the left side of the engine, reach down behind the cylinder head.
Figure 6

Working from above the left side of the engine, reach down behind the cylinder head. Disconnect the crankshaft sensor electrical connector (red arrow) by pressing the plastic release tab and pulling it straight off.

Testing with sensor installed: Next, connect two jumper wires with insulated spade terminals to the crankshaft position sensor terminals (red arrows).
Figure 7

Testing with sensor installed: Next, connect two jumper wires with insulated spade terminals to the crankshaft position sensor terminals (red arrows). Then connect your DVOM to the jumper wires and turn it to AC Volts. Crank the engine over. The sensor should produce about 0.5 volts A/C when cranking.

Testing with sensor removed: Remove the E8 crankshaft positon sensor fastener.
Figure 8

Testing with sensor removed: Remove the E8 crankshaft position sensor fastener. Once the fastener is removed, pull the crankshaft position sensor out of the engine block. It will slide straight out. 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 the 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 (yellow arrow) is static to an RPM reading of 20 up to 1500 RPM (red arrow), depending upon how well you break the magnetic field.

Testing with sensor removed: This photo shows the sensor removed and unplugged from the vehicle.
Figure 9

Testing with sensor removed: This photo shows the sensor removed and unplugged from the vehicle. Connect two jumper wires with insulated spade terminals to the crankshaft position sensor terminals. Then connect your DVOM to the jumper wires and turn it to AC Volts. 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 DVOM should go from 0 volts a/c when wrench (yellow arrow) is static to about 0.5 volts a/c when the wrench is moving across the tip of the sensor, depending upon how well you break the magnetic field.



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