1.8T Intermittent Oil Pressure Warning Light - Diagnosis Help Needed!

[A4orce84]

Hello Everyone,

Another day another issue with my B6 it seems. I know not a lot of people are on the forums these days (compared to Facebook and Reddit), but I'll still start here with all the OGs who may still be around and then possibly post on other places. #B6Life

Basically, I am geting an intermittent low oil pressure warning light (red light) and trying to understand why. All the details on my latest issue are below:
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Car Background:
2004.5 Audi A4 1.8T Quattro with nearly 240K miles. I live in Austin, TX (warm climate) and the car is daily-driven. I recently replaced the following parts related to the oil pressure warning light issue:
-Oil Pump.
-Oil Pickup Tube.
-Oil Pan.
-Oil Pressure Sensor / Switch (replaced in 2024).

The Issue:
I occasionally will get a low oil pressure warning light (red oil can) when cruising around low speeds (neighborhoods, parking lots, etc.). The light turns off if I speed up (going 30+ MPH) or if I turn the car off and on again.

Videos Showing The Issue:

1. https://youtu.be/LAWoryJysYY. ---> Speedup.
2. https://youtu.be/u8IVs7WfhhU. --> Restart car (Turn it off and on again).

Talking with friends and mechanics, due to the miles on the car (240K miles) and age of the car (21 years), everyone recommended replacing the oil pump and oil pickup tube (also replaced the pan). Unfortunately, after having these items replaced, I still get the occasional oil pressure warning light. Also, I do not believe it is the sensor itself, since it was replaced in 2024, AND if it the sensor, I believe I would be getting the low oil pressure warning light constantly (all the time) and not intermittently.

Diagnosis:
I hooked up an oil pressure gauge and at idle it looks like things are within spec at 20PSI.



I have also read through the huge 1.8T oil pressure survival guide as well as a few other posts on the subject:
Link --> https://www.audizine.com/forum/showt...leshooting-DIY

Possible Cause - Theory:
So, my working theory right now is there is a threshold (normal PSI range for oil pressure) that my car's oil pressure dips under occasionally (in low-speed situations), which triggers the low oil pressure warning light. When I speed up / slow down, I am back in the ‘normal range’ of the oil pressure, so the warning light turns off.

The Question Remains:
If my oil pressure dips down occasionally (below the normal range), what is the actual issue? The oil pump, oil pickup tube, etc. have been replaced. So, what else could be the root-cause issue here? Anything else to check here in terms of common issues?
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If I can provide any additional details from my end to assist in the troubleshooting process, please let me know. If anyone has any ideas / feedback / thoughts /etc. on what the possible root-cause of the issue is, it would be greatly appreciated!

Thanks,
Asif

[old guy]

Possible explanation: Clicky click

[Cybersombosis]

What oil weight are your using?

[A4orce84]

Possible explanation: Clicky click

Fletcher! Good to see you still around these parts of the internet sir! Thanks for the information that is super useful from 10+ years ago! I will do some investigating with my PCV and see if I can find anything obvious. I know I switched over to the 034 PCV kit, but that was 10-12 years ago at this point.

Thank you sir! =)

[A4orce84]

What oil weight are your using?

Currently, I am running 5W-40 oil with my 1.8T.

I know I can run something a bit heavier, in terms of oil weight, and that may end up being a Band-Aid fix for the time being. At the very least it's cheap insurance and shouldn't be an issue with the Texas summer heat that will be starting soon (100+ Degrees Fahrenheit).

[EuroxS4]

What is the source of the oil pressure sensor that was installed and was the connector checked? Also have you tried putting in some lucas heavy duty oil stabilizer? It's like engine honey. It does it's job rather well. I would lean towards a pcv issue or oil check valve in the oil filter block assembly.

[A4orce84]

What is the source of the oil pressure sensor that was installed and was the connector checked? Also have you tried putting in some lucas heavy duty oil stabilizer? It's like engine honey. It does it's job rather well. I would lean towards a pcv issue or oil check valve in the oil filter block assembly.

The connection at the rear of the oil filter housing was used for the oil pressure gauge. To answer your other question, I have not used any type of stabilizer or oil additive at this point.

[Larhal]

I hada similar senareo in the begining of this year. I have a 2002 A4B6 1.8 T also, 156,000 miles.I purchased an oil pressure guage kit and also had fluxuating oil pressure ay Idle. Changed the oil,no go, oil stanbliser, no go. changed the oil pressure switch with a new Audi one and havent had an issue since. Could be just the switch failing.

[A4orce84]

I hada similar senareo in the begining of this year. I have a 2002 A4B6 1.8 T also, 156,000 miles.I purchased an oil pressure guage kit and also had fluxuating oil pressure ay Idle. Changed the oil,no go, oil stanbliser, no go. changed the oil pressure switch with a new Audi one and havent had an issue since. Could be just the switch failing.

Perhaps, but I had my oil pressure sensor (oil pressure switch) replaced in 2024 (as outlined in my OP). If my oil pressure sensor was failing, I would think I would be getting the low oil pressure warning light on ALL the time, and not just in the low-speed situations that I outlined above.

[Gin+]

Sounds very reminiscent of the early water-cooled VWs, including my own which had almost no oil pressure at idle when hot.

[Larhal]

Perhaps, but I had my oil pressure sensor (oil pressure switch) replaced in 2024 (as outlined in my OP). If my oil pressure sensor was failing, I would think I would be getting the low oil pressure warning light on ALL the time, and not just in the low-speed situations that I outlined above.

Not always. Mine would come on when hot and going throgh town in 4th or 5th gear. It would go out when I raised the revs in 3 gear. so it showed the same symtoms as yours. I was just shareing my experience.

[Kevin C]

My guess would be that the warning light has some logic built in that keeps it on if it sees a brief low pressure event. From what I have read, the warning is not activated under a certain RPM (i think 2000). There could be some logic in the ECU that keeps the light on for a set period. So if its marginal, and triggers the system just as you cross 2000 rpm, the system keeps the warning lit so that you see it.

The other explanation is a faulty indicator system. The only way to really know is to drive it with a gauge and see what's happening, or just try another sensor.

[EuroxS4]

My guess would be that the warning light has some logic built in that keeps it on if it sees a brief low pressure event. From what I have read, the warning is not activated under a certain RPM (i think 2000). There could be some logic in the ECU that keeps the light on for a set period. So if its marginal, and triggers the system just as you cross 2000 rpm, the system keeps the warning lit so that you see it.

The other explanation is a faulty indicator system. The only way to really know is to drive it with a gauge and see what's happening, or just try another sensor.

OP failed to state source of oil pressure switch. Without knowing where the oil pressure switch came from it's hard to say whether the part itself is any good. These vehicles don't like china shit for sensors installed. OEM to start.

[A4orce84]

OP failed to state source of oil pressure switch. Without knowing where the oil pressure switch came from it's hard to say whether the part itself is any good. These vehicles don't like china shit for sensors installed. OEM to start.

Oil pressure switch was replaced at my local indy Audi shop. OEM Audi oil pressure part was used on my car.

[EuroxS4]

Oil pressure switch was replaced at my local indy Audi shop. OEM Audi oil pressure part was used on my car.

Who supplied part and what source and part number?

[A4orce84]

Who supplied part and what source and part number?

I'll try and dig up the receipt and see if I can find the part number and OEM information. Appreciate your help!

[A4orce84]

Mini-Update:
I was recommended to try a heaver weight oil, as a Band-Aid fix, for the summer months here in Texas. I ended up going with the magical E46 BMW M3 Synthetic oil that everyone recommends and switched over specifically to Liqui Molly 10W-60 weight oil. I am PLEASED to inform everyone that after a few days, and a 400-mile drive over the weekend, I have not gotten any low oil pressure warnings!

I'll do some more investigating in terms of the root-cause issue (sounds like PCV could be the most likely culprit), but at least for the summer months, I am glad everything with the B6 is now a bit more 'stable' for the short-term.

Thanks in advance to all of you for your time and help. I really appreciate it! =)