Oil pressure warning light comes on intermittently

[redding]

A few weeks ago while driving home, my oil pressure light came on as I was pulling into my driveway, and I immediately turned off the engine. I routinely check my oil level so knew it was good, but checked it anyway and confirmed it was topped off. Some google searching led me to replacing the oil pressure sensor in case it was faulty. Afterwards it drove fine, but about a few days later the oil pressure warning light came on again.

At that point, I did what I should've originally done which was to use the oil pressure switch testing procedure in the manual, and I verified the switch and the pressure is good. However, since the warning light rarely comes on, and does so at random, I couldn't test the pressure while the warning light was on.

I haven't driven it since, for fear it'll lose pressure while I'm driving somewhere that I can't turn off the engine fast enough.

I read somewhere that fragments of "junk" can get into the oil pan, sometimes covering the oil pickup. Someone said it's likely a fragment from a cracked timing belt cover, since they said those are known to crack. I even found one video on the interwebs of a guy with the same issue on his TDI - he dropped the oil pan and found a few fragments an inch or two in size, but he wasn't sure what they were.

I have tools and some know-how (do all my own maintenance less timing belt), so I am willing to drop the oil pan to remove any fragments if that's the best way forward. But I'm thinking if there is a cracked timing cover (or something else), it should be dealt with or could eventually drop more fragments into the pan.

I'm inclined to drop the pan to check for and remove any fragments, but have a few questions (below) and am open to any suggestions:

1. Is this likely caused by fragments in the oil pan blocking the oil pickup?
2. What are the most likely souces of those fragments?
3. Assuming it might be the lower timing belt cover, how hard and time consuming is it to inspect to see if it is cracked?

 

[Nero Morg]

Well firstly you should identify if it's a wiring issue or a mechanical issue. The single wire for the oil pressure switch can get brittle and break in several spots. Hooking up a mechanical gauge and verifying your actual pressure is good is also another good test.

I'm willing to bet it's a wiring issue. Have you changed the oil recently and see any metal shavings? Metal can come from any place in the engine.

 

[Zak99b5]

How would part of a timing belt cover get into the oil sump?

I'd suspect a piece of an old dipstick "funnel" instead.

But yes, use the mechanical gauge as Nero suggests first.

 

[gforce1108]

You can install a T then watch the gauge and look for the light at the same time.

 

[Genesis]

What they all said; figure out if you have a mechanical or electrical problem FIRST. This is not something to toy with as loss of oil pressure under load will catastrophically damage the engine in seconds.

 

[paul_cat]

Very likely just a bad sensor, a $10 part. After 20 years it's bound to be glitchy. Replace it in just 5 mins. They go by color, yours is likely brown. It's located below the oil filter containment, easy access. Inspect the [single] wire to be sure it isn't fraying.

 

[TurboABA]

Very likely just a bad sensor, a $10 part. After 20 years it's bound to be glitchy. Replace it in just 5 mins. They go by color, yours is likely brown. It's located below the oil filter containment, easy access. Inspect the [single] wire to be sure it isn't fraying.

He's already replaced it.
The fact that it was "fine" for a while and then it started again after said replacement, would nudge me to think it's a wiring\connector issue.
Inspect all that closely. Teeing in a gauge is the best way to verify that you're not about to damage anything.

 

[BobnOH]

Brief care history?
My 1st TDI (99.5J) had the oil pan compromised, lots of oil loss, then driven on freeway, in winter. I drove with intermittent oil pressure light for months. Couldn't find the issue myself, had to seek professional advise. I changed the bearings (after replacing perfectly good pump and sensor) car ran great for 8 years, until daughter played pinball with some concrete barriers.
Couple things I learned; Oil pressure is only monitored at certain RPMs, the pump throws oil to the top of the engine, much of the actual pressure is generated by the bearings.
When you pull the pan, remove 1 or 2 bearing caps and check the bearing. The fix, replace all rod and crank bearings, was way easier than I anticipated. One note- The car only had 40k miles.
Bad bearings photo

 

[redding]

I tested the oil pressure in my driveway and when it was still cold I got 60 psi @ idle and 85 psi @ 2000 rpm. Once fully warmed up the readings were 21psi @ idle and 44 psi @ 2000 rpm. The only spec I see for the TDI ALH in the bentley manual is 36 PSI (minimum) @ 2000 RPM. Since pressure drops as oil warms, I'm thinking my 44 PSI is good. I don't think the 21 psi @ idle is anything to worry about, what do you guys think?

Sounds like the consensus here is that its more likely to be an intermittent wire problem, rather than an intermittent oil pickup blockage. So the next step is to replace the old wire and connector and verify the problem does not return in time.

Has anyone here change that wire and connector before, that can provide some guidance? I see the wire goes into a larger band of wires and up towards the firewall. Wondering what the proper procedure is here, and if I can avoid opening up the band of wires, and maybe add a new wire to the outside somehow. Anyone have a reference to instructions on how to change that wire, and whether is runs straight into the instrument cluster?

 

[Nero Morg]

I don't recall exactly how the circuit works, but where the wire comes out of the harness to just the single bit to the connector, that's where it usually fails. I've even seen the wire snap inside the insulation, pulling on the connector it literally pulled apart if cut it off close to the harness and just run a new wire, see if that takes care of it.

 

[paul_cat]

try putting some dielectric grease into the connector to the sensor and attach it on and off a few times to wipe the pin down. perhaps intermittent will go away.

 

[redding]

I sprayed the connector with CRC Contact Cleaner and cleaned it up a bit. We'll see if that helps. I did notice the connector won't click in the way its supposed to. When I push it in all the way, it wants to push slightly back out. The inner clip on the connector seems to be fanned out just a little to much to grab the trangular hook on the sensor. I tried pushing it slightly with a small screwdriver, and it stays in place but I'm not convinced its grabbing how its supposed to. I do remember when I first pulled it out, it was pushed in all the way and grabbing good, so although this is all the more reason to replace the wire/connector, probably wasn't my original issue.

 

[Nero Morg]

In a pinch you can use a regular female blade terminal on the sensor. Done it twice, no issues on either car 2+ years later on each.

 

[Zak99b5]

In my 84 Jetta GLi the oil pressure warning would buzz occasioanlly. I'd just smack the dash and it would stop.

 

[JB05]

I agree with the faulty wire concensus. The wire is very thin and lives in a hot environment. I had to change that wire for that very reason.

 

[redding]

A couple of questions about changing the wire and connector. Do I need to buy a special heat-tolerant wire? Any links for where to buy it? And do I have to take apart the wire bundle and replace the entire length of wire all the way to the dash cluster, or just a section of the wire?

 

[Nero Morg]

Just replace the section of wire that's bad, you don't have to reinvent the whole circuit.

Repair Wire 000 979 131 EA [Gold 1mm 205C]

High-temp rated, 1mm diameter wire with 2 connectors. Used in small connectors such as the reverse light switch and fan control module connector....

www.idparts.com

I believe this is the repair wire you need.

 

[vandermic07]

I think Nero is right.

I had flakey reverse lights in my Jetta Wagon. I replaced the switch, re-soldiered the wires (it has a 6 speed swap). Still had the issue. Found that the one pin in the plug was sloppy. Fixed with a repair wire. Good to go.

 

[redding]

While waiting for the new connector/wire (shipping delays), I dropped the oil pan and noticed metal shavings in my oil pickup screen, thought not enough to block it completely. Could this have been the cause of the intermittent oil pressure light? Considering my TDI has 230k miles, are some metal shavings expected/acceptable, or is this a cause for alarm?

oil-pickup-screen-2.jpg

• redding
• May 2, 2022

oil pickup screen w/metal shavings

oil-pickup-screen-1.jpg

• redding
• May 2, 2022

oil pickup screen w/metal shavings

underside-baffle.jpg

• redding
• May 2, 2022

oil pan removed, showing baffle

underside-1.jpg

• redding
• May 2, 2022

oil pan removed

oil-pump-and-chain.jpg

• redding
• May 2, 2022

oil pump and chain

oil-pump.jpg

• redding
• May 2, 2022

oil pump

crankshaft-2.jpg.jpg

• redding
• May 2, 2022

crank

crankshaft-1.jpg

• redding
• May 2, 2022

crank

chain.jpg

• redding
• May 2, 2022

oil pump chain

baffle-2.jpg

• redding
• May 2, 2022

oil baffle removed

baffle-1.jpg

• redding
• May 2, 2022

oil baffle removed

 

[redding]

Anything else I should do while the pan is off, other than clean it up and put things back together?

 

[BobnOH]

Maybe pull one crank bearing and one rod bearing to check.
bad bearings

 

[Genesis]

I don't like seeing things like that...... I think I'd look around some.

 

[Mongler98]

Stuff like that can easily be from when a service was done and something was dropped.
Definitely not enough to raise alarm. This is what there is a screen and we have filters.

 

[Nero Morg]

I second what Mongler said, I don't quite identify the metal, but that doesn't mean it wasn't from the engine originally.

Keep in mind that the rod and I think main bolts are stretch bolts, one time use! So if you inspect the bearings be prepared to replace them.

Before pulling the caps, inspect the oil filter for debris. Anything smaller than the mesh of the pickup tube will show in the filter.

 

[redding]

I figured out where the metal shavings came from. Someone helicoiled the drain plug threads.

Doesn't explain the low pressure though. Is there anything that can cause low pressure light besides clogged pickup, bad sensor, connector, or wire? If it was a bad pump, would it be so intermittent, only coming on once or twice a week, then going away after I shut off the car for a few minutes?

Basically I want to know if I can safely ignore the intermittent low pressure light now that I've seen the intake isn't clogged - until I receive and install the new connector and wire.

 

[Nero Morg]

I would put a mechanical gauge on it first before saying yes.

 

[redding]

I could put in a permanent pressure gauge near the oil pressure sensor. Is there instructions on how to do that for a 2001 Jetta mk4 alh?

 

[Nero Morg]

Just get a tee and plumb it in next to the factory sensor.

 

[Mongler98]

If you must go with a gauge I highly suggest AUBER.
they are more than just a gauge. And it's one of the highest quality gauges you can buy that is also very affordable.

 

[vandermic07]

Those metal particles look like machining chips possibly from the factory. Probably stuck on holes in the block