Volkswagen Cars 2000-05

Low Oil Pressure Warning Sensor

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Volkswagen uses a two-sensor system to alert the driver of the vehicle of oil pressure status. These sensors both indicate a low oil pressure condition.

The Dynamic Oil Pressure Warning System consists of two oil pressure sensors, a warning light and buzzer, and an electronic control unit, mounted inside the instrument cluster.

The low pressure sensor is normally closed (causing the oil pressure light to flash) until the engine is started, and idling. At idle, the oil pressure is great enough to keep the switch open, preventing the light in the instrument cluster from flashing.

The high pressure sensor (normally open) operates in conjunction with electronic control unit. The electronic control unit receives reference signal from the tachometer when it reaches 2000-2500 rpm. If the high pressure switch is not closed before the engine reaches approximately 2500 rpm, the electronic control unit will illuminate the oil pressure light.

Removal & Installation



Removal of the switch is simply a matter of unscrewing it from the cylinder head/oil filter housing. When installing the switch, apply a light coating of thread sealer to prevent leakage. Tighten the switch to 18 ft. lbs. (25 Nm).

Testing




WARNING
If the oil pressure light in the instrument cluster is flashing while the engine is running, it should be assumed that an oil pressure problem exists. Before performing any electrical testing, the oil pressure should be checked with a mechanical gauge. If the mechanical oil pressure gauge indicates little or no oil pressure, the oil pump and pressure relief valve should be inspected and repaired/replaced as necessary. If the oil pressure is correct, proceed with electrical testing.


NOTE
The switch pressure is usually inscribed on the switch itself.

If the oil pressure has been verified by a mechanical gauge, and the switches are functioning properly, the electronic control unit inside the instrument cluster is faulty, and should be replaced.

On all 8 valve engines up to 1992, and the 1.9L AAZ engine, the low pressure switch is located on the side of the cylinder head, and the high pressure switch is located on the oil filter housing. On VR6, 16 valve and 1993 and later 8 valve engines, (except for AAZ) both switches are located on the oil filter housing.

High Pressure Switch
  1. With the engine idling, disconnect the harness connector from the high pressure switch.
  2.  
  3. Raise the engine speed to 2500 rpm; the light should flash.
  4.  
  5. While holding the idle speed at 2500 rpm, ground the high pressure switch harness connector.
  6.  
  7. With the high pressure switch harness connector grounded, and the idle speed above 2500 rpm, the light should cease to flash. This indicates that the circuitry in the instrument panel is operating properly, and the switch is faulty.
  8.  

Low Pressure Switch

When the engine is not operating, the switch is grounded, which causes the oil pressure light in the instrument cluster to flash. When the engine is started, oil pressure rises, opening the circuit. The function of the circuit can be checked by using a test lead and grounding the pressure switch wire.

  1. Start the engine, and disconnect the harness connector from the low pressure switch.
  2.  
  3. With the engine idling, check that the light in the instrument cluster flashes; if so, the circuit is functioning properly.
  4.  
  5. Using a test lead, ground the low pressure switch harness connector with the engine idling. The oil pressure warning lamp in the instrument cluster should extinguish.
  6.  
  7. If the instrument cluster warning lamp extinguishes, the switch is faulty.
  8.  
  9. If the instrument cluster warning lamp continues to flash while the harness connector is grounded, an open circuit exists between the harness connector and the instrument cluster. Refer to Section 6 for more information.
  10.  

 
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