Dynamic Oil Pressure Warning System Operation and Testing.
In the beginning oil pressure warning lights were very simple devices and earned their nickname of idiot lights. The light was powered from dashboard circuitry and grounded through the oil pressure switch. The oil pressure switch usually opened between three and five psi turning off the light. If the oil light ever came on while driving it was usually to alert you that it was too late.
The Dynamic Oil Pressure Warning System adds a considerable enhancement to the oil light warning system. There's now a high pressure switch that is normally opened, it closes at 1.8 bar. If the engine rpm is over approximately 2000 rpm while the switch is still open, the electronic control unit flashes the warning light and sounds the warning beeper. This is a far better system than the earlier system as it can warn you in advance of impending engine problems.
Dynamic Oil Pressure Warning System problems are most often just that, Dynamic Oil Pressure Warning System problems.
The diaphragms and the springs inside the switches get old and lose tension, the switch contacts can corrode from age and use.
It is very simple to test the control circuitry. With the key on and engine off the oil pressure light should be on steady on early cars, or blinking on later cars. Disconnect the yellow wire from the terminal marked "WK" ("Wahrning Kontraption" in German ) on the dual sender on the left side of the cylinder head, (this is the low pressure switch), the oil light should go out. Start the car with this wire disconnected, light should remain out. Ground this wire and light should come on and remain on as long as this wire is grounded.
Disconnect the blue/black wire from the white, high pressure switch on the oil filter flange and rev the engine over 2000 rpm. After approximately a two second delay the light and warning beeper should come on and remain on no matter what rpm the engine is running until the blue/black wire is grounded.
There are 4 oil sensors on these cars if you have both the Dynamic Oil Pressure Warning System and console gauges.
1) The smallest on the oil filter flange is a variable resistance temperature sender for the console gauge, sorry, Bentley doesn't show the wire color, it's a gauge sender, this thread is about lights and buzzers, so no more about this one now.
2) The other, bigger one on the filter flange should have a white body and a blue/black wire connected. This one is the high pressure switch. It is a normally open contact switch, it is spec'd to close at 1.8 + - 0.2 bar. If engine rpm is above approximately 2000 RPM and this switch is open, the light and buzzer should come on, the control unit has sensed less than 26 psi at 2000 RPM after an approximate 2 second delay. Once this switch has has opened while RPM's are over 2000 after the 2 second delay, the light and buzzer will continue regardless of the engine RPM until the switch closes to ground again.
3a) The combination switch/sender on the side of the head has a variable resistance sender for the console oil pressure gauge marked "G", it should have a blue/yellow wire connected. When the wire is unplugged, the pressure gauge in the console should peg, when grounded, should read zero.
3b) The combination switch/sender on the side of the head has a normally closed pressure switch spec'd to open at 0.3 + - 0.15 bar marked "WK" ("Wahrning Kontraption" in German), it should have a yellow wire connected to it. Any time this wire is connected to ground, the warning light should come on. If this wire is disconnected, there should be no light, even with key on, engine off. Any time this yellow wire connects to ground, the oil warning indicator should be indicating.
3c) Cars without an oil pressure gauge have a brown switch in the side of the cylinder head, it's function and specs are identical to "WK", above in 3b. It's part number is
056 919 081 C. This switch is a cheap easy replacement for a failed "WK" section of the dual sender described in 3c, screw it into an unused pressure port on the oil filter flange, the wire will stretch the distance and connect right up. The only drawback to this "mod" is the location for checking pressure. When located in the head, it reads pressure at the lowest possible location, re-loaced to the filter flange, the oil pressure is at it's highest possible. Note that 16V engines locate both switches in the filter flange as do ABA engines in A3s that also have lower pressure spec switches. It appears to me, by the later model lowering of the specs, the system was too sensitive as originally configured, VW lowered expectations and un-needed warranty claims by decreasing the sensitivity.
Quick, simple diagnosis of Dynamic Oil Pressure Warning System by symptom.
Assuming your engine has oil and hasn't yet started knocking, most likely causes of oil lights/buzzers are in the warning system itself.
1) 2 seconds after 2000 RPM or more, light and buzzer come on, replace the high pressure switch.
2) Oil warning light on at idle, especially when hot, replace the low pressure switch.
3) No oil light blinking with key on, engine off, replace low pressure switch and/or repair light in instrument cluster.
4) If these quick tips fail to address oil warning light/buzzer issues, do not pass go, head immediately to your nearby mechanical oil pressure gauge store and buy a gauge. Buy or make a 10 x 1.0 mm threaded adapter. Test your oil pressure, cold and hot. Know what you are looking at. Check the specs in Bentley.
An oil pump pumps or flows volume, resistance to flow causes pressure. Think of a garden hose with an open end and a pressure gauge at the faucet. The longer the hose, the higher the pressure, if a very short hose is used, pressure will be very low, flow will be maximum. Squeeze the end of the hose, less water comes out but it sprays farther, flow decreased, pressure increased.
Same same inside an engine only the resistance to flow is the clearances between the bearings and the journals. Tight clearances in a fairly fresh engine makes for high oil pressure, worn clearances allow higher flow within the pump's capacity but lower pressure.
Once an engine is running, there is essentially no direct contact between the bearing surfaces and the journals, the journals ride on a pressurized film of oil. Adequate oil pressure is essential for engine longevity.
Oil pumps do fail, but it is very rare. It's real obvious when they go, driver has become instant pedestrian, engine is severely knocking or locked.
Oil pumps also wear over time, but rarely enough to cause pressure loss. If a pump shows wear, the bearings are usually worn worse.
In our engines, a low oil pressure remedy often recommended is a 2.0 oil pump. It works as a patch only. The 2.0 pump has longer gears, it can move more volume and may be able to keep up with worn bearing clearances. It is only a patch delaying the inevitable catastrophic engine destruction.
Thanks to VW's marvelous Dynamic Oil Pressure Warning System and simple loss of spring tension inside the switches, along with real flaky gauges, our cars are often mis-diagnosed as having low oil pressure. Whenever in doubt about oil pressure, check it with a known good mechanical gauge screwed directly into the engine.
In response to a vwvortex thread, "While on the subject of oil pressure lights..."
used to see a lot of brand new, just out of the box, aftermarket
switches that were no good, too many factory switches too. These parts
were so bad, (these light/buzzer issues have been common for a long
time), I took to batch, bench testing our inventory, sending the junk
back right away. I had an adjustable pressure regulator set up for easy
fit up, used a DVOM for continuity testing. The control units are quite
sensitive, they really want to see a fully closed or fully open contact
from the switches.
Some additions from another vwvortex thread to posibly
clarfiry different sender issues , "Hot, hot day,
low oil pressure - Follow up" ,
For those of you that read my original thread, you know that I was going to try a new dual oil pressure sender, the one that mounts on the head. I tried it yesterday. Just as my mechanic who tried it originally told me, it doesn't work correctly. The low oil pressure LED flashes constantly at idle when it is installed. The p/n for this new unit is 035919561A and is rated at 0-5 bar and 1.8 bar.
I think the dual unit I actually need is rated at 0-5 bar and 0.3 bar. German Auto Parts have them for about $50.
My car only has 2 oil pressure senders. the other one is the high pressure sender mounted on the oil filter flange is p/n 056919081E, has white insulation, and is rated at 1.6 - 2.0 bar. I think this is the correct one for that location.
The best I recall is that system was used on U.S. produced GTIs (sometimes considered Rabbit GTIs).
© Ron, tolusina on the 'tex