Volvo 240/740/760/780/940/960 1990-1998

Crankshaft Position Sensor

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OPERATION



See Figure 1



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Fig. Fig. 1: The CKP sensor and pulse wheel

The Crankshaft Position (CKP) sensor, sometimes called an RPM and/or impulse sensor, is used to determine engine speed and Top Dead Center (TDC). This ensures precise ignition timing. The sensor is located at the rear of the engine block, above the flywheel. Engine speed is transmitted to the fuel control unit. The engine will not start without this signal.

LH Jetronic and EZK Ignition System Vehicles

On the pulsewheel, there are 60 markings for the CKP sensor, 58 which are drilled holes to provide information to the ignition control unit. There are no holes at 2 of the markings. These are 90 degrees Before Top Dead Center (BTDC), for cylinders No. 1 and No. 4. Ignition timing is based on these markings and other information such as engine load and temperature. This means that ignition timing can be controlled and that there is no need for the ignition setting to be adjusted.

Regina Engine Control and REX-1 Ignition Systems

On the pulsewheel, there are 44 markings for the CKP sensor, 40 which are drilled holes to provide information to the ignition control unit. There are no holes at 2 of the markings. These are 90 degrees Before Top Dead Center (BTDC), for cylinders No. 1 and No. 4. Ignition timing is based on these markings and other information such as engine load and temperature. This means that ignition timing can be controlled and that there is no need for ignition setting to be adjusted.

Motronic Engine Control Systems

The flywheel has a series of holes located on the top surface. As the holes pass the CKP sensor, the holes induce a voltage in the coil of the sensor. The passage of several holes generates an A/C signal, the frequency of which is a function of the number of holes passing per second and the voltage of which can vary between 0.1 and 55 vdc, depending on engine speed and temperature.

At 90° TDC for cylinder 1 there is a longer hole. When the longer gap passes the sensor, the voltage stops, and the ECM can calculate camshaft position.

TESTING



See Figures 2 and 3



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Fig. Fig. 2: CKP sensor terminal identification

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the sensor connector.
  4.  
  5. Using an ohmmeter, measure the resistance across the two sensor terminals.
  6.  
  7. Resistance should be between 200-500 ohms. If the resistance is out of range, replace the sensor.
  8.  



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Fig. Fig. 3: Testing the CMP sensor resistance

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Remove any components necessary to access the sensor.
  4.  
  5. Unplug the sensors connector.
  6.  
  7. Remove the two retaining screws and remove the sensor from the engine.
  8.  

To install:
  1. Install the sensor into place and tighten the retaining bolts.
  2.  
  3. Plug in the connector.
  4.  
  5. Install any components removed to access the sensor.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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