I have a 2002 A8 that has been great except for one nagging issue - I cannot get rid of the "oil sensor" error light! I have now replaced the sensor two times (the orginal error was a low level warning), and have spent numerous hours trying to check wiring, etc. to determine and correct the cause. I am temporarily able to reset the error by connecting two of the wires, but the error occurs again in approximately one minute. Does anyone have a wiring diagram, or any experience with this issue?

Here is what I have found thus far - it is a three wire sensor mounted on the bottom of the oil resevoir.
red/green wire - 12V input (actually reads about 10.5V)
red - ground wire
grey - return wire for 12V signal?

When I unplug/disconnect the senor completely, I get the "oil sensor" error message; when I plug it in, I still get the same error.
If I briefly connect the red/green to the gray wire, the error is cleared for about 1 minute. I have not been able to find (through trial and error) any method to jumper wires together, or to ground out any combinations to keep the error away.

Does anyone know a way to completely bypass the sensor? If I could do this, I might be closer to finding the root cause. I have contacted the sensor manufacturer, and they would not provide any electical schematics or design info.

The only reference I keep seeing on the internet is "wiring damage by rodents" - I have not seen any indication of this, and unless I can get connection information for the sensor wiring (where it connects into the main electical box), I cannot verify wire continuity to eliminate this scenario.

Audi "stealer" has recommended replacing the sensor (yet again), and then will proceed to replace the wiring harness.

I am not interested in spending $500 to start, and who knows how much from there - at this point it is just a ridiculously annoying riddle I am determined to solve! Any help would be greatly appreciated...

Thanks in advance for any thoughts, advise or technical info.

 

According to wiring diagram, gray w/yellow stripe wire is + straight from fuse...green w/red stripe is signal to indicator unit control module in instrument cluster...brown is ground.

It's a "thermal" level switch, so depends on oil temp hitting probe in oil pan at a high enough level to register.
When you short the green/red and grey/green, you are likely sending a "completed circuit" signal to the indicator control module.

Don't know where your problem lies, but this diagram shows all connections and colors. Hope it helps you to trace or bypass the problem.


oillevelsensor1.jpg?t=1293986015

oillevelsensor2.jpg?t=1293986077

 

Thanks very much for the response. I will decode the schematic you sent, and see if I can solve it from there. I agree, the brown (it looked red) appears to be ground, and the green/red is a 12V signal to the sensor.

Does this expalin why I was never able to trigger a "low oil" message with all of my electrical ground/jumper attempts?

Any suggestions on why I can reset the "oil sensor" warning, but it seems to keep triggering itself quickly (1 minute) thereafter? Is there anything else you suggest that I can check to isolate and repair cause of this error?

 

Hey Silverd2: I like you photo in the snow covered wilderness !!! Is that in east Tenn.?

What source did you get your 'oil level sensor' wire diagram ?? Pretty sharp image...

 

The wiring diagram is actually a photo of my computer screen (Bentley CD Rom), then cleaned it up a bit in Photoshop. Never have figured out how to tranfer files directly...Bentley makes it difficult (if not impossible).

Yep, my sig pic, over on QW, is East TN at a mountain valley pasture in the Smokies where we keep the horse. We live way up on a wooded mtn side, a few minutes away from there. That was taken just a week ago.

 

Just a guess:

The oil sensor warning is apparently indicating that the control module has lost contact with the sensor...no signal, good or bad.

It may not be possible to fake a low oil warning signal, since it's a thermal oil level switch (and if control unit has lost touch with the sensor?).

But shorting the 2 wires together could be sending a "sensor in contact" signal by bypassing the sensor completely. If it resets the warning light, that would indicate that wiring from there to the control unit is OK...it probably just takes a minute for the system to check sensors (or requires a timed test) to determine that it's out of touch again.

Logically, this all points back to the sensor again...internal open circuit or contacts on the sensor(?)

Don't know why 2 sensors in a row would fail, though...odds aren't with it.

BUT, I don't know enough to tell you that it couldn't be the control unit (or for sure wiring to it...doubt that, though)...would need a known "good" sensor to prove that.

 

I have run an independant ground wire to the harness to ensure that is not the issue.

I have tried every combination of jumpering to get the "sensor error" to stay off, but to no avail. If I ground the 12V feed, it does reset the error, but withing 1-2 minutes, I get it again.

I have seen some posts regarding a VW with the same sensor and the same error, and they indicated you could totally bypass the sensor by putting a jumber between the two non-ground wires (red/green and grey/yellow)for a fix, but even this does not work for me after 2 minutes.

Anyone have any ideas on how I can just cut the wiring at the sensor (or even further up into the witing harness), and permanently bypass it?

This is my only complaint with my A8, and I am going slowly insane trying to eliminate it...

 

Did you check the fuse for it/ It is on the blue fuse carrier.

 

Sorry to ask a simple question, but what fuse are you referring to? (the main fuse panel is the passenger footwell, or the one on the right side in the trunk?)

Thanks in advance.

 

I did find the 5amp fuse blown in the passenger footwell (in the blue blue fuse strip). I was able to replicate the fuse blowing by jumping the red/green 12V feed wire to the grey/yellow return wire.

I have now replaced the 5A fuse, and am able to reset the "oil sensor" error manually (I think it is when I ground the 12V feed), but it still only remains "OK" for 1-2 minutes - the "oil sensor" error ALWAYS returns!

What can I try now?!?!

Fundamentally (from the previuosly posted wiring schematic), is the "proper" sensor operation when the 12V feed passes the input voltage back to the grey/yellow line?

1. I assume when the sensor error is designed to occur, it is when the input voltage is "open" (e.g same as when the sensor is totally unplugged).
2. I reasoned that when the 12V signal provides a return signal to the grey/yellow line, it would logically either trigger a "low oil" or "OK" condition.

Is it possible that the sensor has a