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The fourth generation Volkswagen Jetta, also called the MK4 or the Bora, is Volkswagen's family sedan.

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Oil pressure light on

2003 vw jetta 2.0 gas 5 speed manual trans

Oil pressure light is on replaced the switch and still flashes on the dash. Hooked up a manual gauge 40 at idle and 60 at 2000prms. Any other ideas? Grounds wires looked good.

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Mike Moos what exact year, model and engine size is it?

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Hi,

Here’s the Engine Lubrication System section from the 1999-2005 Jetta service and repair manual, that may help.
It details how to test the oil pressure warning system.

Just wondering if the pressure switch wire is earthed somewhere.

Looking at the manual when testing the pressure switch warning system, the lead is disconnected from the switch and an earth is placed on the lead. It says that the warning light should flash and a buzzer should beep 3 times. Not sure if this means that the light should also only flash 3 times or only the buzzer beeps 3 times and the light continues to flash. If you leave the wire disconnected from the pressure switch with no earth lead connected to it then the warning light should not come on. If it does it sort of proves there is a problem on the wire .

Update (04/02/2022)

Hi,

Here's the wiring diagram fro the oil warning light circuit that may help if it comes down to tracing out the circuit.

As noted earlier the rpm seems to be tied in with the oil warning light.

The wiring diagram shows the VSS sensor in the same circuit diagram, so its input to the instrument cluster control module must be used in conjunction with the oil sensor. Hopefully the module is not faulty as far as the oil warning light goes.

Is the speedo accurate and also the tacho (if there is one)?

Block Image

(click on image to enlarge)

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Hi Jayeff,

Well did the test on 17-3 of the manual and all is good it does everything listed. So the next step 17-4 is to do with an oil pressure gauge. I kinda all ready did that with just screwing in a mechanical gauge and I'm within spec. It's just proves the switch is bad and I already bought 2 different ones both with the same 1.4 bar. I'm really stuck on this one car has had no issue every regular oil change etc...

par

@Mike Moos

17-4 also states to use a test lamp connected between the switch (lead removed from switch) and the +ve battery terminal and make sure that the test lamp does turn on when the oil pressure =1.4bar

Can only suggest that you disconnect the lead from the pressure switch and connect a test lamp between the switch terminal and the +ve battery terminal

Start the engine and check if the test lamp comes on.

Also it seems as though the oil warning light is related to the engine rpm as it says that if the lead is left disconnected, then when the motor is at idle the warning light should not come on but if rpm is increased to 1500-2000 rpm it will, so presumably if the lead or switch was faulty i.e. no earth received by ecu from switch you would only get a warning light at increased revs and not at idle.

Stupid thought maybe but check if the engine block has a good earth connection. If there is only one wire connected to the oil pressure sensor then the sensor must be getting an earth through the body of the sensor where it threads into the engine block to pass on to the ecu when it operates at 1.4bar. If the test light doesn't come on at all then either the switch is faulty (I know you have tried 2 different ones)or it is not picking up a good earth connection where it threads into the engine

When testing with the lamp be safety aware when the engine is running

par

Yes, the light and buzzer is off at idle and comes on at about 1500rpms. I'll test again this weekend. I'll look for grounds also.

Thanks

par

Jayeff,

Hooked up the test light between the positive side of the battery and the switch light comes on when it should off at idle. Also connected the test light to the negative side of the battery and the lead wire and the dash light goes off so I'm assuming it's a ground issue somewhere. Then thinking if I connect a lead to the negative side of the battery and the outside housing of the switch maybe it'll go off but it didn't light was still on in the dash. I just might try adding another ground tomorrow from the engine block to the body.

par

yes speedo is accurate and it does have a tach.

par

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Try tracing the oil pressure sending unit wires back to the light in dash, there could be damage along the way. Meanwhile, I would have a manual gauge hooked up permanently.

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