HOWTO: Diagnose the Dynamic Oil Pressure Warning System
Sunday, 08 March 2009
Do any of these symptoms sound familiar???
“My oil light has started to come on when my car is hot”
“The oil buzzer goes on after I’ve driven on the highway for
a while… if I rev the engine the buzzer goes off”
“My oil light came on but my oil level is fine”
“My oil buzzer comes on when the engine slows to around 2000 RPM….
It’s fine at 3000 RPM or at idle.”
Any of the above are telling you it’s time to check out your
oil pressure. Note I said “pressure” not “level”… the warning system does not
detect low oil level (unless the level is so low the oil pump sucks in air of
course).The warning lights and buzzers
may be the sign of broken wires or sensors OR you may actually have an oil
pressure problem.If this is the case you
are shaving months off your engine’s life every minute you keep driving.
Low oil pressure problems are typical of high-mileage VWs
with worn bearings and oil that is hot and therefore thin.The combination of thin oil and worn
bearings means that the oil pressure is marginal at lower RPMs where the oil
pump is not spinning as fast as it does on the highway.
In order to understand why this happens we need to understand VW's interesting warning system.
VW uses an oil pressure warning system that has two sensors.
(1)A conventional low-pressure sensor, usually on the driver’s side of the
head.
It is normally closed and opens at
0.25 bar.The car always pays attention
to this sensor and when this sensor trips the low pressure light comes on.This is the sensor that turns on the low oil
pressure light when you turn the key to “on” without starting the car.This sensor is not connected to the
oil pressure warning buzzer.It’s
typically blue in colour and is connected to the wiring harness with a blue/black wire.
Note that on 16V and V6 gassers this sensor is usually located on the oil filter flange.
(2)A hi-pressure sensor located on the oil filter flange.
It is normally open and closes at
a fairly high pressure depending on engine type ( 1.8 bar for gassers, 1.4 bar for normal diesels and some turbo diesels, 0.9 bar for MK3 turbo diesels).The car only watches this
sensor when the engine is over 2000RPM and when this sensor goes off the oil
buzzer will sound and the oil pressure light to flash.It’s typically white, grey, or black in colour and is connected to the wiring harness with a yellow wire.
Why the compexity? The idea is that oil pressure that's OK when the engine is idling is not the same pressure that's OK when you're roaring down the highway. At idle a pretty low pressure is fine, but that pressure would be a big problem at highway speeds. Hence, a warning system that knows the difference:
Schematically, the system looks like this:
Troubleshooting:
Now that we understand the dual-sensor of the oil warning
system troubleshooting is pretty straight forward:
- a flashing light, by itself, is the
function of the low pressure sensor on the head
- a flashing light and
buzzer are a function of the high-pressure sensor on the filter flange.
- the car only looks at the high pressure sensor when the car is over 2000 RPM.
Troubleshooting steps:
1)Warm the engine up to full operating temperature (rad fan has
cycled at least once) and then shut the engine off.
2)Turn the key to “on”; the oil pressure warning light should
come on thanks to the lo-pressure sender on the head.If the light doesn’t come on there’s a problem with the
lo-pressure sender, the wiring to that sender, or the dash cluster. A test
light between the sensor and the positive battery post should light when the
car is off and go out when the car is idling, if the sensor is ok.
3)Start the engine… the oil pressure warning light should go
out.This tells you the engine has oil
pressure appropriate for idle. If the light does not go out you have
low-pressure sensor problems or oil pressure problems:STOP and figure it out before driving away !
4)Slowly rev the engine
up to 2500 RPM… the light should stay out and the buzzer should be quiet.If the buzzer sounds you need to
troubleshoot the hi-pressure system:
a.Disconnect the wire to the hi pressure sensor on the filter
flange and let it dangle.The oil
buzzer should now come on above 2000 RPM
b.Now ground the yellow wire and rev the engine past 2000 RPM… the
buzzer should not sound.
c.If you fail either of these tests you have sensor issues, wiring, or
cluster issues.
d.A test light between the sensor and the positive battery
terminal should be off at warm idle and come on as you rev the engine, if the
sensor on the flange is working properly. If the buzzer still sounds with the wire to the sensor grounded the problem is most likely the wiring to the cluster or the cluster itself.
If you have a diesel:
As you now knowthe
cluster needs to know engine RPM in order to tell which sensors to
monitor.If you have a diesel the
cluster reads RPM from the W terminal on the alternator.If that signal is missing or erratic, your
tach will be doing funny things and so will your oil pressure warning
system.Often oil pressure buzzer
issues show up at the same time as a tach issue.In particular, if your tach reads too high it may trick the cluster into expecting the oil pressure to be high as well, and the buzzer will go off.
I seem to have low oil pressure… what can I do ??
The first thing to do is to confirm you really have an oil
pressure problem.A cheap oil pressure
gauge (Napa, Autozone, Canadian Tire, etc) connected to the oil filter flange
will let you measure the one specification VW gives:
2000 RPM
oil at normal operating temperature (rad fan has cycled
once)
2 bar (29 psi) minimum
<picture of cheepo gauge>
Note that the test spec is given with the engine hot… get
out there for a spirited drive and bring your engine all the way up to full
operating temperature before taking an official reading.
If your oil pressure is almost OK (ie gets dodgy around 2000
RPM) there are a few things you can try to buy yourself a little time:
switch to a thicker oil… something like a good 20W50
for summer driving (if you live in a reasonable warm climate) or a wide range synthetic... something like a 5W40 or 5W50
ensure you are running a quality OEM (Bosch, Mann, etc)
filter … the cheap ones (particularly the one in the orange can) are known to
not flow as well as stock
check to see if your engine is overheating and
therefore overthinning the oil
If these bandaids don’t do the trick it’s time to break out
the wrenches:
pull the oil pan and check to see if the oil inlet
screen is clogged with crud
remove the oil pump and check for wear… the Bentley
manual shows the procedure which uses feeler gauges to measure a couple of key wear points.In truth
they very rarely wear out… they are a robust design and are the best-lubricated
part of the engine, but it’s only two bolts to confirm.I personally don’t recommend arbitrarily
replacing the oil pump at the first sign of oil pressure trouble… as I say they
very rarely fail.
Tear down the engine and replace the main and rod
bearings.Although not recommended,
this can be done with the engine in the car after pulling the oil pan.
If you have a diesel the intermediate shaft bearings
are a common wear area due to people overtightening the timing belt, and they
can cost a lot of oil pressure when they start to flake.For all intents and purposes the engine has
to come out to replace the intermediate shaft and bearings if you have a transverse-mounted engine (Rabbit, Golf, Jetta). Folks with Quantums and Foxes can evidently get to it without pulling the engine, as per the comment below.
Hi Vince, very good explanation, but I have another oil pressure indicator issue. Car is a Passat B4 TDI. Normal signalling of oil pressure system is working OK (i.e. indicator lights up with ignition turned, blinks and buzzes when wire from hi pressure switch is pulled), but during a normal driving the oil pressure indicator light (a red LED to be precise) very faintly glows, continously. Do you have any idea where to look? This happens both with a cold and a warm engine. Oil pressure verified OK with a pressure gauge. Please, any ideas?
Hi Mark: it takes very little current to make a LED glow... so it is likely a poor connection somewhere. Since it occurs at all RPMs it's probably on the low-pressure side... does the dim LED glow go out when you pull the wire off the low pressure sensor?? If so the sensor is defective. If not... you can trace the sensor wire along the harness... it may have rubbed bare somewhere and is grounding itself a bit.
Another possibility is the cluster itself... swapping out a known-good cluster is the quickest way to isolate that problem. A bit of moisture on the circuit board can cause phantom current paths very easily.
In the end, if you can convince yourself that you'l see a solid LED for both low and high pressure switches, you may decide to just ignore.
Let us know what you find!!
Vince
... written by K. Stewart,
June 20, 2010
Hi:
Would you be able to clear up some conflicting info on your web site. My 1985-1992 VW Service Manual Section 3:41 says the lower oil pressure switch is on the filter flange and the higher one is on the end of the head. However, on 3:43 there is a picture which shows the high pressure switch at the filter flange. Which is correct??
Thanks
Hi there... yes the Bentley is conflicting sometimes.
The paragraph on page 41 of chapter 3 that reads "the low pressure switches are located on the oil filter flange (0.3 bar) and the end of the cylinder head (1.4 or 1.8 bar) is in error, in my opinion.
On that same page figure 7.1 shows the higher pressure switch on the flange, and as you mention fig 7.6 on page 43 of that same chapter also shows the higher pressure switch flange.
This has always been the case on any VW with dual sensors I've seem and also makes sense... I'd expect the most pressure to be at the flange just after the pump, with the least amount of pressure at the tail end of the head. It's also the case that previous engines with only one sensor had the 0.3 bar sensor at the head.
All in all... I believe how the system is represented on my HOW-TO is accurate: higher pressure switch on the flange and lower pressure switch on the head.
Vince
... written by zia,
June 13, 2010
Hi recently i changed my oil and than i noticed when i drive over 2000 rpm the buzzer goes on what can i do to fix it im living in small island in thailand and the local mechanics don't know what the problem is after putting a new motor oil and checking the only oil sensors on oil filter , he gave up on me , do you have any suggestions thanks
Hi Zia... if you follow the instructions in this HOW-TO step-by-step you should be able to figure it out... you will want to focus on the oil pressure at the high-pressure sensor on the oil filter flange, the sensor there, or the wiring to it.
As per my instructions above, I'd start by getting a mechanical gauge hooked up to see what your oil pressure really is.
Vince
... written by Talon,
April 07, 2010
I have 1.8 Golf and the Oil light comes on and the buzzer sounds at low RPM (engine warmed up)and they go out if I rev up the engine? No lights or buzzer while cold. It would seem to be a low pressure situation but with the high pressure warning?
... written by Ian,
April 01, 2010
You have helped me with the timing a year or so. Now I have a 90 diseal Jetta with no tack. I have a crashed car with a instrument pannel with one. Is it a easy thing to change the insterment pannel and hook up the tack and all the different gauges. Is the wiring harnes in the car with out the tack got the wirering in it? I have the generator from the crashed car and all the parts. If you could help It would be greatly appreacieted . Ian
... written by Erik,
February 07, 2010
Ive had similar experiences and know several ways to get rid of that pesky buzzer, in a safe reliable fashion. first thing ive noticed is through all of my vw's, over the years the oil screen in the oil pan (one the bottom of the oil pump, clearly visible after it drips in your eye) that gets blocked up. take down the pump by three easy screws, buy replacement seal or wing it, and remove lower pump tube. its got two screws. use a can of brake cleaner and clean inside and out,scrubbing with an old toothbrush. the crap gets lodged inside the tube and you cant see very well from outside so dont be satisfied with a cursory inspection. at 180k (miles) i replaced my oil pump just because while these engines do last, a srop in oil pressure over time is expected and any losses are much more critical to an older engine. other problems include restrictions in oil travel, for which i only recommend BG products oil flush (in the red can). works a champ. i flushed my motor before cleaning the screen last, and replaced the pan gasket. problem solved. on another note if you have a loose connention to your oil pressure senders this will also trigger the warning buzzer but is rarely the cause. take care to unscrew them and spray clean the hole in the end, to allow proper readings. thank you!
... written by Ant Harvey,
January 20, 2010
Hi - great article. I think I know, from what I've read, what my problem is but I want to double check. My 1.8 8v Mk2 GTI runs great, no smoke, no knocks, even idle, no overheating etc. When it warms up (oil at 90 deg and water at first marker - as high as it goes) the oil light flashes at idle, anything over 1000rpm and its off. It either flashes regularly or today flashed very quickly and intermittently, just stopping for a split second and rapidly flashing again. From cold it come on as you turn the ignition then straight off. Can you give me your opinion? many thanks, Ant
... written by Rick,
December 30, 2009
I was able to change out the intermediate shaft bearings in my MKII Jetta by removing the front and rear motor mounts and tilting the belt-side of engine downwards. I then removed the intermediate shaft through the passenger side wheel well.
... written by Hennie Stander,
December 05, 2009
Hey man,good article! Quick question.. I removed my mk2 1.8l 8v head recently because a water port corroded and caused the head gasket to fail. Had the head welded and skimmed and installed it again. Car runs nicely,engine sounds good,but since i installed the head,i'm suddenly getting the oil buzzer problem when i've driven the car hard for about 30miles,rev it,and it goes away.. I'm using the same 20w50 oil i've always used.. is there anything in the head that can cause the car to have low oil pressure since the repair? Thanks
Hi Hennie... thanks for your comments.
That's a strange one for sure. Since it's the buzzer and it's going away when you rev it has something to do with the hi pressure sensor circuit/sensor on the oil filter flange.
I can't actually think of anything you could do to the head that would cause low oil pressure directly at the flange. As per my writeup I'd recommend getting a pressure gauge in there to see what's really going on... could simply be a sensor that decided to crap out at the same time as your repairs.
thanks again for your comments,
Vince
... written by Ambet P,
July 07, 2009
WHOOOHAAAAAAAA!!! thanks for this... really a big help!!!
... written by Josh,
May 01, 2009
In diesel quantums, the engine need not be removed to replace the intermediate shaft bearings. With the radiator out, the condenser rotated up and out of the way, the grill off, and the front engine support removed, you can jack the front of the engine up enough so that the center line of the intermediate shaft can be accessed via a slot in the front end. Via this slot, you can extend a threaded rod, and utilize the procedure for installing and removing both intermediate shaft bearings utilizing home made or custom crafted(recommended if you don't have a lathe)tooling as described in the "show us your custom tools" sticky thread over at the vwdieselparts.com/forum site.
Hey Josh... thanks for the useful suggestion... I've updated the HOW-TO to reflect your additional information.
Vince
... written by Cale,
April 12, 2009
Great article, friend. Thanks for helping us keep our cars in good shape. Long live the Mk2.
Subscribe to this comment's feed
Car is a Passat B4 TDI.
Normal signalling of oil pressure system is working OK (i.e. indicator lights up with ignition turned, blinks and buzzes when wire from hi pressure switch is pulled), but during a normal driving the oil pressure indicator light (a red LED to be precise) very faintly glows, continously. Do you have any idea where to look? This happens both with a cold and a warm engine. Oil pressure verified OK with a pressure gauge. Please, any ideas?
Hi Mark: it takes very little current to make a LED glow... so it is likely a poor connection somewhere. Since it occurs at all RPMs it's probably on the low-pressure side... does the dim LED glow go out when you pull the wire off the low pressure sensor?? If so the sensor is defective. If not... you can trace the sensor wire along the harness... it may have rubbed bare somewhere and is grounding itself a bit.
Another possibility is the cluster itself... swapping out a known-good cluster is the quickest way to isolate that problem. A bit of moisture on the circuit board can cause phantom current paths very easily.
In the end, if you can convince yourself that you'l see a solid LED for both low and high pressure switches, you may decide to just ignore.
Let us know what you find!!
Vince