EPC light
 

Hello, I have a 2011 Audi A4 2.0T 4 door sedan TFSI that has EPC light comes on every time I accelerate the car over 4000 RPM whether it is in sport mode or manual shifting and after that it will not go past 4000 RPM and will automatically shift every time it is in sport or manual and the instrument cluster displays "do not exceed max engine speed of 4,000 RPM". I did not have this problem before. It gives the code"5580-P164B Oil Pressure Switch Malfunction_" under the category "Engine Management". I have already changed the oil pressure switch two times to make sure that I didnt buy one thats not working, the replacement one is OEM. I have tried deleting the code after installation and taking it for a drive but problem is still the same. Thanks.

P164b and ECM light
 

I have the exact same symptoms on a 2011 A4 2.0T
There are quite a few owners who report this problem but there doesn't seem to be an acknowledged fix.
There are two oil pressure switches labelled F22 and F378 on the factory manual wiring diagram:
F22 oil pressure switch (Blue below the oil filter and harder to reach)
F378 reduced oil pressure switch (Brown - the upper easy accessible one)
The brown one has specs 0.5-0.85 bar and the blue one 2.15-2.95 bar.

I have replaced both mine with no effect. Some owners report broken wires, so in order to trace I opened up the electrical box and connectors underneath the washer fluid filler.
The manual wiring diagram lists no less than 6 different wiring diagrams for these switches with different wiring colors. As both my switches had white/grey wires I chose that diagram. My brown switch was supposed to go to Pin 40 on the 94pin connector and the blue switch to pin 18.
The brown switch checked out with continuity to pin 40. Great! The blue switch failed. After wasting a lot of time looking for breaks I discovered there actually is NO wire at all going to pin 18. The wiring diagram is incorrect. Because the wire from the blue switch disappears into the wrapped loom I can't find where it goes at all. Besides, it doesn't look like it could be damaged anyway.
So that leaves me still totally perplexed as to what this P164B code means. It would be helpful if the code said WHICH oil switch. Maybe there is a third oil switch I don't know about.
All very frustrating.

More thoughts on the meaning of P164b
 

Thinking about this a little more: How can the ECM know an oil switch is bad? The switch is either off or on when it reaches specified pressure.
The only way it could know (for the brown switch) is if the higher pressure switch comes on when the lower limit one hasn't triggered. If the higher (blue one) doesn't switch on, then it means EITHER the switch is bad OR oil pressure is too low.
As this error only occurs when you rev up to 4000rpm I'm thinking there is logic which says "If rpm >3500 and blue oil switch not on, then trigger code 164b"
and actually the meaning isn't "Oil switch malfunction" but (if you have a new oil switch like me) but "Hey dude! Your oil pressure should be much higher at 3500rpm.
I'm gonna get an oil pressure gauge and check this theory out.

Oil pressure low
 

Just to add a little more to this story:
I checked my oil pressure and it looks like this:
RPM ............ Specs .................... Actual
Idle - 1.2 - 2bar (17.4 - 29)psi 14psi
2000rpm - 1.6 -2.2bar (23 - 31.9)psi 29psi
3700rpm - 3.0 - 4.0bar (43 - 58)psi 38psi

Below spec at idle and above 3500rpm.
Our cars have the self-regulating oil pump that operates in two modes. Around 3500rpm it changes to the second mode.

The N428 valve is used to make the change. I checked mine and it gets voltage at idle and it also buzzes inside if I apply 12v to it. Other than that I don't know a way of checking it.

Both my oil switches I have double checked for switching at the right pressure (with a meter and an air compressor) and they are good. (Although I now think that P164b error is for the blue higher pressure switch and error code P164d is for the reduced pressure brown one)
I also checked continuity back to pin 46 of the 94pin connector under the washer filler (for the brown one) and back to pin 5 of the 32pin connector to J519 under the dash. ( for the blue one.)
With no problem with the oil pressure switch I think the error P164b is actually incorrect when it points to the oil switch. I think it's more likely saying, "I reached 3500rpm and the oil pressure should have been 40psi by now and it isn't, so I think the pressure switch must be bad." Of course, it could also simply mean your oil pressure is low at higher rpm.

I went ahead and dropped my sump to check the pickup tube. It was all clear and the oil was pretty clear too except for some tiny rubbery gasket pieces.

This car did have the intake balance shaft freeze up in its bearings so there does appear to be an oil problem somewhere. It just seems impossible to determine where!

P164b update
 

The blue oil pressure switch (04E 919 081 A) is usually marked to switch on at 2.55bar or around 37psi. Currently my engine is not reaching 37psi at 3700rpm.
So if your oil pressure switch is good and you still get P164b the ECM is telling you "Hey! your oil pressure is too low at 3700rpm!"
Take note that the ECM will only run this check if the engine has reached normal operating temperature, because the oil hasn't thinned out properly to get the lowest reading until then. Sometimes this will take 10 to 15minutes in my car.

Thanks for the detailed diagnostics. This has helped me troubleshoot my own engine. I'm in the same boat. Just wondering if you ever resolved it. Did you have to replace the oil pressure regulator?

Update
 

I have since sold this car, but I managed to reach the point where the error code no longer appeared when revving above 3500rpm.
I did replace the oil pump/regulator with an after market pump, but I don't think it made much difference to the oil pressure. I did discover that there is a slight variation in the oil pressure switches, i.e. exactly when the switch triggers. I can't remember right now which manufacturer was better but I switched my replacement out for another one and then (don't tell the Audi gods), I added a quart of 15W50 oil. Because the oil pressure is so close to the pass/fail value, that was enough to fix it even when the oil got hot.
Of course, there is some deeper problem here probably involving the piston rings, but the only options left were a complete engine rebuild and I wasn't going to do that.
If you need more specifics I can check my notes.

It turns out it was a broken connector in my case. The plastic tab was angled in such a way that inserting it into the switch caused it to angle downward more, blocking the electrical connection. I didn't realize (lack of experience with these connectors) that it wasn't clicking and locking. Anyways when realigning that tab I broke it clear off. So now it doesn't seal against the little orange silicone gasket. It does make. Electrical contact though, so I can Rev past 4krpm again. But that said, the connector should be replaced, it would not be good if it came loose again...

So that was fun to trouble shoot. Good oil pressure, wires fine, switch is good, all that was really left was the connector, I'm not really used to connectors being a problem... Lesson learned.

Hopefully this helps anyone else that sees this issue

This might help!
Epc light was on with my Audi for long time. Fighting speed and all other lights keep coming on. My battery went out and I changed to a new one and everything went away. I don't know if new battery did the job but so far epc light, engine light are off two weeks and still off.

if you guys have any more explanation please share with me.