Can a bad oil level sensor cause low oil pressure warning?

[vlad]

I got the dreaded red oil can warning last week. I had it towed to the shop and they hooked up a pressure gauge and found that oil pressure was good (70 psi). So the mechanic said they replaced the oil pressure sensor but also said I need to replace the oil level sensor. Well, I just replaced the oil level sensor myself maybe 4 months ago and haven't had an oil level code since. I explained that to him but he said the oil level sensor can cause the oil pressure code too. That doesn't sound right to me. Is there any truth to that?

He said they cleared all the codes after replacing the oil pressure sensor and still saw the oil pressure code again which is why they needed to replace the oil level sensor. When I asked for more info about that and explained how I had just replaced it myself with a genuine audi part that I had purchased from their shop, he sort of mumbled quickly that they had already replaced it and he would have to call me back. So I'm waiting for a call back now.

[walky_talky20]

No. There is no truth to that.

And what is this 70psi number? What exact oil temp and rpm does that correspond to?

[vlad]

Yeah I didn't think so. Thanks for the quick confirmation.

He didn't specify rpm or temp for that reading. I was under he impression that a low pressure situation would result in pressures in the range of 20psi or lower for all conditions so I was just happy to hear something higher than that. What would healthy pressure readings be under various conditions? I'll be sure to ask for clarification when he calls back.

[coowhip]

Oil level sensor is just that. ^Trust the Walky. Your shop guys seems like he doesn't know what he's doing. I recommend a tow to a proper repair shop asap before it gets too deep.

[vlad]

Ugh, yeah unfortunately this is the only place I know of within a 200 mile radius. They are supposedly the audi/vw specialists for this town...

[coowhip]

Which is what town?

Also, get specific information for whatever codes he is giving you. Paper printouts, pics, etc... Verify verify verify.

[vlad]

Which is what town?

Also, get specific information for whatever codes he is giving you. Paper printouts, pics, etc... Verify verify verify.

I live in Missoula MT. Know any Audi guys over here?

[coowhip]

Me personally, no. I assume you took the car to mountain imports?

First thoughts on the problem, clogged oil pickup tube or oil pump. Have to drop the oil pan to see. If you are going to drop it, might as well do both while your at it.

[vlad]

Me personally, no. I assume you took the car to mountain imports?

First thoughts on the problem, clogged oil pickup tube or oil pump. Have to drop the oil pan to see. If you are going to drop it, might as well do both while your at it.

Yup, mountain imports is the only game in town. Don't even have a dealership here. They replaced my master cylinder for me not too long ago and I was happy with the job. This is a very different experience though.

I was thinking pickup tube or pump too, but when he told me it was the sensor I was happy. Again, he practically hung up on me when I challenged him on the oil level sensor before I was able to get more info. When he calls back I should know more. I'm not going to have them drop the pan if the pressure is normal though.

[walky_talky20]

I don't have access to a B6 Bentley, but this is the oil pressure warning criteria from the B5 Bentley Manual:

- Engine switched off and oil pressure switch still closed
- Coolant temp less than 60C AND engine speed higher than 300 RPM AND oil pressure switch open
- At coolant temp over 60C, warning is recognized when oil pressure switch is open for more than .5 seconds above 1500 RPM. If this condition occurs more than 3 times during a drive, the warning will stay active even below 1300 RPM.
- At engine speed greater than 5,000 RPM, an active oil pressure warning will not be erased, independent of oil pressure switch input

Notice it is based on coolant temp and not oil temp. I would assume the criteria is the same for the B6, but I cannot be certain without looking at the manual. Perhaps another member will chime in.

And as far as the pressure goes, just because it makes 70psi doesn't mean it's good to go. You need to check the pressure at an oil temp of 180F or higher. Idle pressure should be 20psi or better. 1500 RPM is the magic number: the warning threshold. The switch has to be closed by then. And that requires up to 23psi. To evaluate the oil pressure you really need readings at idle, 1500, 2k, 3k, 4k, and 5k. All taken at 180F+.

[vlad]

^^ Thanks for looking that up for me. I'll be sure to ask for a detailed report regarding what specifically they measured.

[walky_talky20]

Looking up the info on this shop, they seem to be good people.

For the pressure, it can be tricky. It can appear to be good under a normal test. For example, good idle pressure and 70psi at 3k. But if you push it to 5k RPM and the pressure drops to 55psi, you've got a problem. One that could even trip the warning light under certain conditions.

[vlad]

Yeah I've never had any real complaints about them before. I'm wondering if they maybe just don't see this issue very often. I asked him yesterday if they would check the pump if they had to drop the pan and he said no, the pump pretty much never fails, they usually just replace the pickup and call it good. That wasn't quite the answer I was hoping for, so I told him not to do anything without consulting with me first. I figured if they were going to drop the pan I might want them to replace the pump anyway. As of this point I haven't given them the OK to do anything except check the pressure. It's been six hours since he called me to tell me the pressure was fine so it should be an interesting conversation whenever they get around to calling me again.

[walky_talky20]

Our shop has never replaced a pump either. We've done tons of pickup screens, though.

[vlad]

Good to know, I'll probably take their word on the pump then

[vlad]

So I swung by the shop on my way home and had a chat with the tech who was working on my car.

-He only tested the pressure cold and said he didn't wait for it to get hot or check at various RPM. So 70psi was measured before the oil got up to temp.
-Replacing the oil pressure sensor didn't help. The code remains under all conditions. The oil level sensor didn't factor in at all. (They replaced it then swapped it back when they saw that it didn't help)
-A note on the oil level sensor: He said it could trigger the red oil can because it is also a thermal sensor. So it can trigger both the yellow oil level warning and the red oil can. This is contrary to the notion that the oil pressure warning is based on coolant temps though. I think.

Final diagnosis: Bad instrument cluster! This is kind of where he lost me. He said basically that he could see that the signal from the oil pressure sensor to the cluster never changed under any conditions, on or off or at higher RPM or after clearing the codes. Something like that. And he had another Audi identical to mine apparently that he was able to compare the signal with to determine what it should be doing. I can't explain this well because he was trying to dumb it down for me and wasn't using any of the proper terminology, so I'm not sure exactly what signal he is referring to. It almost sounds like condition 1 listed from the B5 Bentley manual though.

Does any of this make sense to anybody? Could it possibly be a bad instrument cluster? The diagnostics didn't sound very convincing. Isn't there a straightforward way to tell if the instrument cluster is bad?

Some additional background: The oil pressure warning went off last week for the first time as I was pulling away from my house. As soon as I went over about 1500 RPM it triggered. And it does that parked as well. I turn the car on and there is no warning, but as soon as I rev it a bit to about 1500 RPM the warning triggers. The tech explained that for that reason (that it happened under cold conditions and not while hot or under load) it doesn't sound like a typical low pressure condition. Thus lending more evidence to the fact that the instrument cluster is bad.

[walky_talky20]

- I really don't think the oil level/temp sensor can trigger a low pressure warning. It is true that a bad level/temp sensor can trigger a few different types of warnings, but I don't believe a pressure warning is one of them. i could be wrong. But you and the tech have ruled out the level sensor anyway.

- The tech is absolutely right that this does not seem like the usual low oil pressure/sludge issue that is typical of a 1.8T. Your pressure is probably quite fine, and you just have an electrical issue here.

- If the tech was saying that he got no signal change at all from the pressure switch, even with the engine off compared to running/revved, then there is your problem for sure.

A: The next step is to perform the test as described in the bentley manual. Basically you are unplugging the pressure switch and checking its output directly. The Bentley procedure uses a fancy factory tool: an LED tester with a gauge and such, but that's really not necessary. You can just use an LED test light between the positive battery terminal and the switch output pin. Or you can use a multi-meter to check resistance between engine ground (valve cover) and the switch output pin. Check it with engine off (should be open circuit or LED off) and check it at cold idle (should be approx 0 ohms to ground or LED on).

B: Once you determine that your pressure switch is giving the correct output signals, then you test your wire. It's just 1 wire. It runs from the switch to the cluster. Test it end-to-end to make sure the wire is good. You can even use your LED test light to 12V+ to make sure you see the pressure switch signal operating correctly right at the back of the cluster.

*Alternatively, you can repeatedly open and ground the wire in the engine bay whilst you watch the value in VCDS to see if it changes accordingly. That's probably preferable to step B. It's a quicker test, but you are testing the wire and cluster at the same time, instead of separately. If this test fails, you then have to pop the cluster out and do test B above, to check the wire only in order to get a positive diagnosis on a bad cluster.

If A and B check out, but your cluster still doesn't see the correct signal, THEN you have a bad cluster.

I really doubt it's a bad cluster. It's possible, but I'd bet it's the wire, the connector, a bad ground to the sender, or something like that. The symptoms you describe point to the cluster never seeing the ground signal from the pressure switch. Ever. So, for example, a break in the wire would perfectly explain your symptoms.

[vlad]

The way you are describing it, I think these are the steps the tech already took in diagnosing the cluster. He was speaking quickly and in vague terms so I wasn't following everything, but I'm pretty sure those are the tests he was describing. I know he did remove the cluster to do some testing after describing a situation where he saw no change in signal using vag com when opening and grounding the wire.

I think I'll pick up a used cluster and swap it out and see if that helps.

Thanks for the input, it has been really helpful.

[imnuts]

If the signal is not coming to the cluster itself, then the sensor, or the wiring from the sensor to the cluster is bad, not the cluster. The only way to verify that the cluster would be defective would be to give it a bad signal and see if it gives you the warning, then clear the signal and see if the warning clears.

[walky_talky20]

^Yep. This is what we described. Supposedly the tech has given fake signals to input pin at the cluster, and still no change on the logic side in VCDS.

So, whilst this failure is rare and I have in fact never heard of one failing this way, due to the info provided and diagnostic steps described I'm going with a solid: "Seems legit."

The replacement cluster will need to have the immobilizer matched up to your ECU. This is do-able without a dealership, but the official response is "only the dealer can do it". I'm interested to hear which avenue they take on that. Unless you plan to do it yourself.

[vlad]

^Yep. This is what we described. Supposedly the tech has given fake signals to input pin at the cluster, and still no change on the logic side in VCDS.

So, whilst this failure is rare and I have in fact never heard of one failing this way, due to the info provided and diagnostic steps described I'm going with a solid: "Seems legit."

The replacement cluster will need to have the immobilizer matched up to your ECU. This is do-able without a dealership, but the official response is "only the dealer can do it". I'm interested to hear which avenue they take on that. Unless you plan to do it yourself.

Oh, well I was thinking of doing it myself since it looks pretty straightforward, but matching the immobilizer to the ECU doesn't sound like something I know how to do. Do you know if there is a way to DIY?

Any danger in buying a used cluster? Found a part-out on craigslist, could pick the cluster up for $100. Seem reasonable?

[walky_talky20]

Yep. Used cluster is the way to go. You need some tools to make it work, though. To be able to reset the mileage to be accurate for your car, as well as get the SKC for immobilizer matching.

Like myah:
https://sites.google.com/site/imnuts/

And hmyah:
http://www.ebay.com/itm/Vag-Tacho-3-...649736&vxp=mtr

And...
https://www.youtube.com/watch?v=J5_51qeEyec

[MikeWire]

Vlad, you're in Missoula...do I know you? There's also Import Palace over on W. Broadway.

[vlad]

Vlad, you're in Missoula...do I know you? There's also Import Palace over on W. Broadway.

Well, I'm not sure. Do you know a tall guy with red hair named Vlad? Can't be too many of those around town. Are you in Missoula too?

Do you have any experience with import palace? Do they know our cars pretty well? I've been taking my car to mountain imports for stuff I don't want to do myself because I thought it was the only option.

[vlad]

Yep. Used cluster is the way to go. You need some tools to make it work, though. To be able to reset the mileage to be accurate for your car, as well as get the SKC for immobilizer matching.

Like myah:
https://sites.google.com/site/imnuts/

And hmyah:
http://www.ebay.com/itm/Vag-Tacho-3-...649736&vxp=mtr

And...
https://www.youtube.com/watch?v=J5_51qeEyec

Thanks for the info. I'll see what the shop says and then decide if I want to do it myself.

I would be so lost without this forum...

[MikeWire]

Well, I'm not sure. Do you know a tall guy with red hair named Vlad? Can't be too many of those around town. Are you in Missoula too?

Do you have any experience with import palace? Do they know our cars pretty well? I've been taking my car to mountain imports for stuff I don't want to do myself because I thought it was the only option.

Well, I'm not sure, but your description doesn't sound familiar and more likely I would know you from your username. Our local group is bigskyeuro.com (link in my signature), so I wasn't sure if I knew you from there or not. If you want a second opinion you can check with Wes over at Import Palace, they do a lot of VW and Audi work there as well.

Just reading your description, I would ask for the VCDS (Vag-Com) printout for the specific code(s) you are getting, then look them up on the Ross-Tech wiki and use the interweb machine for more detail.

[vlad]

Well, I'm not sure, but your description doesn't sound familiar and more likely I would know you from your username. Our local group is bigskyeuro.com (link in my signature), so I wasn't sure if I knew you from there or not. If you want a second opinion you can check with Wes over at Import Palace, they do a lot of VW and Audi work there as well.

Just reading your description, I would ask for the VCDS (Vag-Com) printout for the specific code(s) you are getting, then look them up on the Ross-Tech wiki and use the interweb machine for more detail.

Oh, yeah I've never gotten involved with the Audi community here. Nice to know about Import Palace now, I'll definitely keep them in mind for next time. Or if I replace the cluster and still am having issues. The service guy I was dealing with at Mountain Imports didn't seem too eager to answer my questions. Every time I asked for more information or about specific codes he sort of waved his hand and made a reference to the tech almost as if he was the wizard of oz or something - all knowing, not to be questioned…

[diagnosticator]

Yes, a faulty level sensor will result in low oil pressure if the oil level alarm light does not illuminate and the oil level is not routinely checked at fuel fill ups, until the oil level falls enough for the pump to start sucking air. Otherwise, no. Not directly.

[vlad]

Got the cluster replaced and no more warning indicator. And my car now has 80,000 fewer miles than it did before!