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Crankshaft Positioning Sensor Replacement
 
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Pelican Technical Article:

Crankshaft Positioning Sensor Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$30 to $120

Talent:

**

Tools:

13mm wrench, 17mm socket, 5mm Allen

Applicable Models:

Mercedes-Benz W124 (1986-95)

Parts Required:

New crankshaft or engine speed sensor

Hot Tip:

Use a mirror

Performance Gain:

Smoother running car

Complementary Modification:

Replace camshaft positioning sensor

The crankshaft positioning sensor tells the car's computer where the flywheel is located in relation to the combustion cycle. The DME takes the signals from both the cam position sensor and crankshaft position sensor and calculates when to fire the fuel injectors and spark plugs. If the crankshaft position sensor is not operating properly, your car will run very erratically or perhaps not at all. 

The sensor is located on the left side of the motor towards the very rear under the oil filter housing where it connects to the bell housing. While it is possible to remove it from above with a series of mirrors, extensions, skinny arms and patience it is much easier to remove from below after you move the starter motor out of the way. 

Begin by safely raising and supporting the vehicle. Then you can loosen but do not need to fully remove the starter motor from the vehicle. Please see our articles on jacking up and supporting your vehicle as well as removing the starter motor. Wear safety glasses anytime you work under your car.

Begin by locating the ground or negative cable on the battery (yellow arrow) and use a 13mm wrench to disconnect it.
Figure 1

Begin by locating the ground or negative cable on the battery (yellow arrow) and use a 13mm wrench to disconnect it. Place the cable in a manner that it cannot accidently touch the battery post while you are working.

The starter is located on the lower left side of the motor (red arrow).
Figure 2

The starter is located on the lower left side of the motor (red arrow). It attaches to the bell housing. Removing the starter motor from its mount will make a difficult job so much easier. You do not need to disconnect the wiring to the starter just get it out of the way. Give the starter a quick wipe down if it is oily as it is heavy. You do not want to drop it once it is free.

There are two 17mm bolts holding the starter motor to the bell housing (red arrows).
Figure 3

There are two 17mm bolts holding the starter motor to the bell housing (red arrows). It is a very tight fit but using a 17mm socket you will be able to remove both bolts. The motor will be free with the bolts removed so do not let it drop.

With the starter pushed forward out of the way it is very easy to remove the sensor.
Figure 4

With the starter pushed forward out of the way it is very easy to remove the sensor. You can just see the top of the sensor (red arrow). Use a 5mm Allen and remove the single nut holding the sensor to the engine (yellow arrow).

Pull the sensor (red arrow) out from its mount and disconnect the sensor from the wiring connection.
Figure 5

Pull the sensor (red arrow) out from its mount and disconnect the sensor from the wiring connection. Note: on some older sensors you need to disconnect the sensor from the wiring where it plugs in in the engine bay.

This photo illustrates the sensor out from the engine (red arrow).
Figure 6

This photo illustrates the sensor out from the engine (red arrow). There is a small magnet on the end of the sensor. There should be nothing attached to this magnet. Installation is the reverse of removal.

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Page last updated: Fri 12/9/2016 02:38:47 AM