Checking hydraulic switches / oil pressure

The 0.3 bar hydraulic switch has brown insulation. On all 4-cylinder engines, it is located on the flywheel side of the cylinder head. On 6-cylinder engines, it is located next to the 1.4 bar hydraulic switch on the oil filter flange. Auxiliary hydraulic switch 1.8 bar in 4-cylinder petrol engines (white insulation) and, accordingly, a 0.9 bar hydraulic switch in diesel engines (gray insulation) mounted on the oil filter flange.

Check oil level.

Check the electrical wires of both hydraulic switches according to the wiring diagram.

Checking the hydraulic switch at 0.3/0.25 bar

Unscrew the hydraulic switch by 0.3 bar (brown insulation), after disconnecting the electrical wire from it.

Attention: From approx. 3/96 to petrol engines with a displacement of 1.8/2.0 l (except 16-valve) Instead of a 0.3 bar switch, a 0.25 bar hydraulic switch with blue insulation is installed.

Screw in a suitable pressure gauge instead of the hydraulic switch.

If a VW measuring device is used, screw the hydraulic switch into the measuring device.

Attention: The test described can only be carried out if the hydraulic switch can be screwed into the pressure gauge. Otherwise, only the 1.8/1.4 and 0.9 bar hydraulic switches can be tested.

Connect the measuring device with an auxiliary wire to ground.

Connect the plug-in contact of the 0.3/0.25 bar hydraulic switch with the auxiliary cable -A- to the positive pole of the battery via a voltage tester. At the same time, voltage should be displayed and the control pump or light diode should be on.

Start the engine and slowly increase the engine speed.

As soon as the pressure gauge shows a pressure of 0.15-0.45 bar (for 0.3 bar switch) or 0.15-0.35 bar (for 0.25 bar switch), the voltage should turn off, and the control lamp of the voltage indicator should go out. If not, replace hydraulic switch 0.3/0.25 bar.

Checking the hydraulic switch at 1.8/1.4/0.9 bar

Disconnect the electrical cable from the hydraulic switch.

Connect the plug contact of the switch with auxiliary wire -B- (6-cylinder engine: VW 1594) through the voltage indicator with the positive pole of the battery. When the engine is not running, there must be no voltage, otherwise the hydraulic switch must be replaced.

Start the engine and slowly increase the engine speed.

When the control pressure is reached, voltage should appear and the control lamp should light up.

Oil pressure check

Start the engine and increase the engine speed to 2000 rpm. At an oil temperature of +80°C, the oil pressure must be at least 2.0 bar.

Insufficient oil pressure indicates worn crankshaft bearings.

Insert hydraulic switch with O-ring and tighten to 25 Nm.