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CoolAirVw · Posted: Tue Mar 28, 2006 8:43 am Post subject: Flashing Oil Pressure Light

I have posted before regarding my flashing oil pressure light. Last month I removed my instrament cluster to repair the odometer as I read on this forum. Odometer is working great, but I have become obsessed with FIXING the flashing oil pressure light. I am going to document my experience on this thread.

#1 I will not disable the light
#2 I will not buy a new part from VW.

Problem: Oil pressure light starts flashing while driving. Note: If left idling the light will not flash. Befere starting the engine the light does flash normally and stops flashing immediatly upon starting as the engine develops oil pressure. Buzzer has never buzzed.

What I have done so far.

Replace both senders with used ones. Checked used senders with Ohm meter. THey do ground when engine is off (no oil pressure) and do not ground when engine is running (oil pressure).

I put a 0-80 psi Snap-On oil pressure guage in the pressure taps at the head and at the filter. Hot engine idling I have 21-26 psi. That is GOOD according to the specification in Mitchell OnDemand.

I checked voltage provided to the senders on the wires. Has 12V on both wires. I monitered this voltage while driving and as the light starts flashing there is no change. Meaning the senders are not grounding and the wire is NOT shorting to ground.

I verified that if I ground the wire to the top sender that the oil light flashes. If I ground the wire to the Lower sender then the oil light does not flash which is interesting but I am ignoring this for now because it seems that this problem would cause the light not to flash.

Will post more later. If anyone sees a step I have missed let me know.
_________________
Richard
85 Jetta TD
ASE Certified Master Auto-Technician with L1 Advanced Engine Diagnostic Rating
ATRA Certified in Rebuilding, Diagnosing & Installing Transmissions

My Threads---> Rusty Floor Repair ---- Oil Pressure Warning----Uploading Pictures----My Porsche 914

tylernt · Posted: Tue Mar 28, 2006 8:07 pm Post subject:

I thought it was a known issue that the dynamic pressure oil buzzer (above 2000rpm) often false-alarmed. I can't remember if it's a relay in the fuse panel or the electronics in the instrument cluster that is the problem, though.

surfcam · Posted: Tue Mar 28, 2006 10:27 pm Post subject:

If the fuel gage is a little off as well. I would suspect the voltage regulator in the instrument cluster might be gone. It knocks the voltage down so it doesn't vary with rpm. It's a little square chip with three prongs coming out of it on the upper left hand corner of the instrument cluster. I had problems with my cluster on my 86 Golf TD. All the gages were out of whack. There's usually lots of gas clusters at the wreckers but few diesel ones. So I slapped the gasser cluster in and run a light to the glows on the dash. Its even possible to get the tack going with a chip from Dakota Electronics. Now I even have a digital clock instead of the stupid shift indicator light.

CoolAirVw · Posted: Wed Mar 29, 2006 5:54 pm Post subject:

I got LOTS more info but I wanted to reply to surfcams comment. Using gas cluster you can change everything over. YOu dont need to run a different light for the "glows" There is a little placard you can change to make the gas cluster read as a diesel. Just take the placard out of your old one and put it in the gas one.

For that matter you can change the tach to the new cluster also.
_________________
Richard
85 Jetta TD
ASE Certified Master Auto-Technician with L1 Advanced Engine Diagnostic Rating
ATRA Certified in Rebuilding, Diagnosing & Installing Transmissions

My Threads---> Rusty Floor Repair ---- Oil Pressure Warning----Uploading Pictures----My Porsche 914

CoolAirVw · Posted: Wed Mar 29, 2006 8:50 pm Post subject:

Ok. More info.

I guessed that the problem may be the oil pressure control unit (OPCU)behind the speedo so I replaced it with a used one I had out of a gas parts car. It did not fix the problem. Sad

So was my used one bad (since it is a common problem) or was it still flashing the light because its now a gas OPCU and its not interchangeable??? That I dont know. But according to some of the other posts on this forum it seems some folks have fixed this problem by replacing a Diesel Instrument Cluster with a Gas. I'm gonna assume for now that they are compatable. If anyone knows for sure let me know.

Since the OPCU didn't fix it I took a good look at the printed circuit with built in resistors and diodes on the back of the instrument panel. There could be shorts or opens in the printed circuit or the resisters could be shorted or open or the diodes could be bad also. So I swapped the printed circuit with the one from the gas car (it had same part number on it as my original). It did not fix the problem. Sad

Will post more later.

by the way I dropped my original OPCU, tripped and ended up stepping on it. Its now in 3 peices. Sad

_________________
Richard
85 Jetta TD
ASE Certified Master Auto-Technician with L1 Advanced Engine Diagnostic Rating
ATRA Certified in Rebuilding, Diagnosing & Installing Transmissions

My Threads---> Rusty Floor Repair ---- Oil Pressure Warning----Uploading Pictures----My Porsche 914

CoolAirVw · Posted: Wed Mar 29, 2006 9:15 pm Post subject:

Just found this. Thought I should include it. (edit pics and links inop now)

Its on this page http://ep0niks.ctech.ca/vw/eva2/EE01/ch7.1.5.html

Someone else recently referred someone there. Thats how I found it.

Oh and here's the index http://ep0niks.ctech.ca/vw/eva2/index.html
_________________
Richard
85 Jetta TD
ASE Certified Master Auto-Technician with L1 Advanced Engine Diagnostic Rating
ATRA Certified in Rebuilding, Diagnosing & Installing Transmissions

My Threads---> Rusty Floor Repair ---- Oil Pressure Warning----Uploading Pictures----My Porsche 914

surfcam · Posted: Thu Mar 30, 2006 1:12 am Post subject:

I would say swapping the gas cluster is a easy fix. I spent hours on the diesel cluster and couldn't get it to work. The oil light comes on if my rpm's drop real low so that and everything else seem to work. I read on a earlier thread that a diesel W terminal on the alternator puts 12 pulse per rpm and a gas put out two so the tack will not work with out a chip. Where is the little placard located.

CoolAirVw · Posted: Thu Mar 30, 2006 4:33 pm Post subject:

Surfcam. You allready replaced your cluster? Did you replace it for a flashing oil pressure problem? Or for a inop odometer?

You stated, "The oil light comes on if my rpm's drop real low so that and everything else seem to work."

Is the oil light coming on after you put the gas cluster in or were you saying that was the reason you replaced it?
_________________
Richard
85 Jetta TD
ASE Certified Master Auto-Technician with L1 Advanced Engine Diagnostic Rating
ATRA Certified in Rebuilding, Diagnosing & Installing Transmissions

My Threads---> Rusty Floor Repair ---- Oil Pressure Warning----Uploading Pictures----My Porsche 914

surfcam · Posted: Thu Mar 30, 2006 9:34 pm Post subject:

I consider the oil to be working normally. Eventually I think I'll get a mechanical gage. The reason I replaced it was because gas and heat gages would not read correctly and I work on the cluster for a very long time with no success. Electrical is not one of my strong suites so the swap was easier for me. Actually it was sort of an experiment to get me though until a diesel cluster show up at pick-an-pull. That's why I was asking you about the little placard because it looks like I might have to do the same thing to my other diesel.

4BTA 3.9 Cummins Stepvan
86TD Golf
91TD Jetta

CoolAirVw · Posted: Thu Mar 30, 2006 11:20 pm Post subject:

So today I'm trying to figure out how the OPCU works. Seems like simple logic doesn't work here. Simple logic would be ground the sender light comes on. So why two sensors? Why OPCU? Is it just there to flash the LED? Why doesn't the LED flash when I ground the lower sensor?

Brad from the forum here e-mailed me the Robert Bently Schematic for the instrument cluster because all I had was the one from Mitchell ON-Demand. Actually I think the one from Mitchell ON-Demand was better. Here is a partial view of the schematic he sent.

_________________
Richard
85 Jetta TD
ASE Certified Master Auto-Technician with L1 Advanced Engine Diagnostic Rating
ATRA Certified in Rebuilding, Diagnosing & Installing Transmissions

My Threads---> Rusty Floor Repair ---- Oil Pressure Warning----Uploading Pictures----My Porsche 914

CoolAirVw · Posted: Thu Mar 30, 2006 11:43 pm Post subject:

OOPs! I'm gonna answer my own question. I found the following in Robert Bently. See link in above post.

7.1 Dynamic Oil Pressure Warning System
The components of the dynamic oil pressure warning system are the pressure switches, the electronic control unit, the low oil pressure indicator, and the warning buzzer. A 0.3 bar pressure switch provides warning when the oil pressure falls to near zero at any time, including at idle. A 1.8 bar pressure switch (1.4 bar on diesels) provides earlier warning, at elevated rpm, whenever oil pressure falls below a minimum safe level.

On 8-valve engines the oil pressure switches are located on the oil filter flange and on the end of the cylinder head. (Fig. 7-1.) On 16-valve engines, both switches are located on the filter flange. On all models, the electronic control unit is behind the instrument cluster.

CAUTION-

If the warning indicator stays on after the engine is started, or flashes on while driving, always assume that there is insufficient oil pressure. Check oil level and test oil pressure before proceeding with tests of the warning system. See 8. Engine Technical Data.

Checking Low Oil Pressure Warning System
With the ignition off, the low pressure switch (0.3 bar) is closed (complete circuit to ground). When the ignition is turned on, the indicator flashes (no oil pressure). When the engine is started and oil pressure rises, it opens the switch (opening the ground circuit), and the indicator goes out. With insufficient oil pressure or a stuck switch, the indicator will continue to flash. The switch opens and closes at specific pressures. See Testing Oil Pressure Switches.

To quick-check the pressure switch, simulate a closed switch by removing the blue/black wire and grounding it. With the ignition on, the indicator should flash. If not, the problem is in the circuit or the indicator. If the indicator flashes only when tested in this way, replace the switch.

If the indicator flashes with the engine running, and the oil pressure tests OK, remove the blue/black wire from the switch with the engine running. The indicator should go out. If not, the circuit is shorted to ground between the wire and indicator. If the indicator does go out, the switch is stuck closed and should be replaced.

Checking Dynamic Oil Pressure Warning System (high rpm)
The 1.8 bar pressure switch (1.4 bar in diesels) is normally open (no circuit to ground). When the engine is running above 2000 rpm (ignition distributor input to control unit), oil pressure closes the switch (completing the circuit to ground). If oil pressure is insufficient to close the pressure switch, or the switch is stuck open, the indicator will flash and the buzzer will sound. The pressure switch opens and closes at specific pressures. See Testing Oil Pressure Switches.

To quick-check the pressure switch, disconnect the yellow wire from the switch and raise the engine speed to between 2000 to 2500 rpm. The indicator should flash and the buzzer should sound. If the wire is connected to ground, the warning should stop. Remove the wire from ground and reconnect to the switch. If the indicator does not go out, replace the switch.

Testing Oil Pressure Switches
The oil pressure at which the pressure switches react can be tested by temporarily installing an oil pressure gauge in parallel with the switch with a T-fitting and monitoring switch performance with a multimeter or test light, as shown in Fig. 7-2. See 8. Engine Technical Data. If the switches are performing properly, the oil pump is producing adequate oil pressure (see 7.2 Oil pump), and the system still warns of low oil pressure, then the dynamic oil pressure warning system control unit behind the instrument cluster should be replaced. See ELECTRICAL SYSTEM.
_________________
Richard
85 Jetta TD
ASE Certified Master Auto-Technician with L1 Advanced Engine Diagnostic Rating
ATRA Certified in Rebuilding, Diagnosing & Installing Transmissions

My Threads---> Rusty Floor Repair ---- Oil Pressure Warning----Uploading Pictures----My Porsche 914

CoolAirVw · Posted: Thu Mar 30, 2006 11:52 pm Post subject:

The thing that stands out to me is that one switch is normally closed and the other is normally open. So just simply putting them in the wrong positions could cause light to flash. Your light could be flashing if your "used part" is normally open and you are installing it where a normally closed one goes. Or maybe your parts guy was in a hurry. Or maybe you dont know the Low Pressure Switch .3 bar from the Dynamic Switch 1.4 bar so your parts guy gave you what you asked for.

Also they are calibrated to different pressures. That might cause problems also.

What also stands out is that my light started flashing at 28 mph. Maybe it wasn't 28 mph. Maybe it was starting at 2000 rpm. I'll double check tomorrow.
_________________
Richard
85 Jetta TD
ASE Certified Master Auto-Technician with L1 Advanced Engine Diagnostic Rating
ATRA Certified in Rebuilding, Diagnosing & Installing Transmissions

My Threads---> Rusty Floor Repair ---- Oil Pressure Warning----Uploading Pictures----My Porsche 914

sideburns · Posted: Fri Mar 31, 2006 12:24 am Post subject:

i had a very similar problem with my oil pressure light and buzzer, very very very very very annoying. after frigging around grounding wires, replacing senders, jumping wires, swapping dashes. i finally pulled the cluster apart, and physically unhooked a wire on a little coil that powers the tach and oil buzzer and smashed the annoying red LED with my vice grips.... i followed the printed circuit and found that, couldnt find the actual buzzer by itself to break some wires.
Thats one good thing about a 20 year old car, i can destroy little pieces of it without feeling bad.

JRM · Posted: Fri Mar 31, 2006 1:50 am Post subject:

on my 85' the light would blink when floored at 60mph in 4th while climbing a 6,000 foot mountain range. I read in the bently that the 85 had a smaller oil pump rotor that was fixed in 86' so I bought a new pump from jack and the light has never came on since
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CoolAirVw · Posted: Fri Mar 31, 2006 8:41 am Post subject:

Sideburns. Your scenario is the same as mine. I've been frustrated by that light for over a year now. Its been flashing ever since I've had the car. That has given me new purpose in life! I will fix that light! I'll keep the hammer and vice grips handy just in case though.

By the way, my buzzer has never buzzed. Probably someone disabled it before I got the car. Dont know how they did it though because of the stuff I've changed.
_________________
Richard
85 Jetta TD
ASE Certified Master Auto-Technician with L1 Advanced Engine Diagnostic Rating
ATRA Certified in Rebuilding, Diagnosing & Installing Transmissions

My Threads---> Rusty Floor Repair ---- Oil Pressure Warning----Uploading Pictures----My Porsche 914