Chrysler Front Wheel Drive Cars 4-CYL 1981-1995 Repair Information

Oil Pressure Sending Unit

Print

OPERATION



See Figure 1

The low oil pressure/check gauges warning lamp (fed by the oil pressure sending unit) will illuminate when the ignition key is turned to the ON position without starting the vehicle. In cluster assemblies without tachometers, the low oil pressure lamp will illuminate if the sending unit indicates that the engine oil pressure has dropped below a safe oil pressure level. The sending unit alters resistance in its circuit depending on the amount of oil pressure detected. (The resistance is raised as the oil pressure is increased). Therefore, the range of various resistances is read by the oil pressure/check gauge and translated into a needle position of the oil pressure gauge. When the oil sending unit receives pressure which below a factory set level, the oil pressure warning light illuminates.



Click image to see an enlarged view

Fig. Fig. 1: The oil pressure switch/sending unit is mounted in the bottom of the dipstick side of the engine block

In cluster assemblies equipped with tachometers, the check gauges warning lamp illuminates when there is a problem in oil pressure level, high engine temperature or low voltage.

The combination oil unit, which is essentially a combination of an oil pressure switch (for the warning light) and an oil pressure sending unit (for the oil pressure gauge), has two functions:



Oil pressure switch-The normal closed circuit keeps the oil pressure warning/check gauges lamp on until there is oil pressure.
 
Oil pressure gauge-The sending unit provides resistance that varies with oil pressure.
 

TESTING



Except TC by Maserati

See Figures 2 and 3

  1. To test the normally closed oil lamp circuit, disengage the locking connector and measure the resistance between the switch terminal (terminal for the wire to the warning lamp) and the metal housing. The ohmmeter should read 0 ohms.
  2.  
  3. To test the sending unit, measure the resistance between the sending unit terminal and the metal housing. The ohmmeter should read an open circuit (infinite resistance).
  4.  
  5. Start the engine.
  6.  



Click image to see an enlarged view

Fig. Fig. 2: Identification of the oil pressure switch/sending unit terminals-except TC by Maserati models



Click image to see an enlarged view

Fig. Fig. 3: Combination oil pressure gauge/warning indicator lamp sending unit schematic-except TC by Maserati

  1. Once again, test each terminal against the metal housing:
    1. The oil switch terminal-to-housing circuit should read an open circuit if there is oil pressure present.
    2.  
    3. The sending unit-to-housing circuit should read between 30-55 ohms, depending on the engine speed, oil temperature and oil viscosity.
    4.  

  2.  
  3. If the above results were not obtained, replace the sending unit/switch with a new one.
  4.  

TC by Maserati

See Figure 4

Click image to see an enlarged view

Fig. Fig. 4: Oil pressure gauge sending unit and low oil pressure warning indicator lamp switch schematic-TC by Maserati

The TC by Maserati vehicles are equipped with separate sending units/switches for the warning indicator lamp on the instrument panel and for the oil pressure gauge.

  1. To test the low oil pressure switch, disengage the locking connector and measure the resistance between the switch terminal and the metal housing. The ohmmeter should read 0 ohms.
  2.  
  3. To test the oil pressure gauge sending unit, disconnect the wiring to the sending unit. Measure the resistance between the sending unit terminal and the metal housing. The ohmmeter should read an open circuit (infinite resistance).
  4.  
  5. Start the engine.
  6.  
  7. Once again, test each terminal against the metal housing:
    1. The oil switch terminal-to-housing circuit should read an open circuit if there is oil pressure present.
    2.  
    3. The sending unit-to-housing circuit should read between 30-55 ohms, depending on the engine speed, oil temperature and oil viscosity.
    4.  

  8.  
  9. If the above results were not obtained, replace the sending unit or the switch with a new one.
  10.  

REMOVAL & INSTALLATION



The oil pressure switch and sending unit is located directly above the oil filter and next to the starter motor on the lower side of the engine block.

  1. Disconnect the negative (-) battery cable from the battery.
  2.  
  3. Unplug the oil pressure sending unit wiring harness connector from the sending unit.
  4.  
  5. Unscrew the sending unit from the engine block.
  6.  

To install:
  1. Install the new sending unit into the engine block and tighten.
  2.  
  3. Plug the electrical wiring harness into the sending unit.
  4.  
  5. Attach the negative (-) battery cable.
  6.  

 
AutoZone Logo