gbmarc

Sorry, but I've made no progress. I installed a new oil control valve and still get the P164b and also the ECM light triggers if I rev above 3500.
Not sure what's left to replace. Obviously the oil pump is probably the next candidate but that's expensive. I'd like to hear another member vouch for how a new pump fixed it, but I don't see any.
Some owners have mentioned how a broken PCV valve has affected the oil pressure slightly, however, my car has no symptoms of, or codes indicating, a bad PCV valve. I also pried the black pancake lid off and the red flex valve thing inside looked fine. (There may be some other components in the other part of the PCV housing that could go bad but I don't think it's very likely on my car.)
I know mine is an oil related issue because I bought my car with a frozen inlet balance shaft that locked up the timing chain. The balance shaft had frozen in it's bearing.
So somehow it hadn't received enough oil. My oil pressure is below specs at idle(14psi) and at 3700rpm(38psi) but OK at 2000rpm(29psi). I also have P0011 'Intake camshaft retard set point not reached', but I think that is related to inadequate oil supply to the camshaft advance adjuster.
I would have thought by now that someone would have seen the fix for this.

gbmarc

Update:
Replaced the oil pump and the inlet Variable camshaft control valve.
The P0011 code has gone. The P164b came back on briefly at 3500rpm when I had the oil level too low immediately after re-assembly, but since I topped it up it hasn't returned. It appears that the oil pump was the culprit. I have the old one on the bench and there's nothing visibly wrong, except perhaps for a very faint kind of binding in the gears occasionally.
Mark

gbmarc

I guess I prematurely declared success.
I have now replaced the oil pump, and still the ECM light comes back on at 3500 rpm. I haven't double checked the codes yet but I'm almost certain that it's still P164b. I'll do that tonight.
The reason that sometimes you think it's fixed is that the engine has to be warm AND revved above 3500rpm for the ECM warning to trigger.
I would even risk trying a second oil pressure switch replacement except for the fact that I manually checked the switch (using air pressure) to see if it would switch on at the required pressure and it did.
This is a very frustrating problem that is reasonably common but obviously a lot more complex than just a bad switch.
I'm surprised that nobody has yet identified a solution.

Mark

Bobby Cummings

​​​​​​Were you able to finally solve it? I'm working on my girls A4 and it's frustrating the hell out of me. I was thinking it could have been sludge since her low oil pressure light would go away above 2000 rpms. So I put in some sea foam and ran it for about 10 minutes and flushed the oil. I noticed the oil was black (the oil was recently changed and had less than 5 miles on it). So since it was black, I did the same thing again and flushed the oil. 3 or 4 times later the oil looked fresh after I drained it. So I figured it was finally clear. But nope, light still comes on. This is the most frustrating car to work on. I've had Mustangs go over 200k without any issue. I have a 95 F150 with 204k miles and it's still going strong. I know that truck doesn't have near the amount of electronics this A4 has, but come on. This is extremely frustrating to figure out.