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Discussion Starter · #1 ·
We have a 2004 XC70 with non-working AWD. I replaced the AOC pump/filter/fluid and the AWD still didn't work. Not wanting to rebuild my DEM if was just the pressure sensor, I went to my local euro car shop and they pulled a DEM code for "Differential oil pressure improper value". They cleared the code and my AWD works now. Is that really how it works? Once the code gets thrown, it just doesn't work anymore until you clear it? Surely it would clear at the next key cycle, right?
 

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I can't speak for this exact scenario, but I bet the answer is not so easy.

Typically if it's a high level warning, even fixing the problem will require a certain number of positive drive cycles to finally remove the stored codes, such as 8 full drive cycles (full cold, full hot, shut down, repeat), or specific things like reaching a speed over XX mph then shutting the engine off for 10 minutes.
Clearing the code w/ a device just over rides any of those requirements.

On the other side of the spectrum, yes, some things will never reset unless you do it w/ the software (i.e. transmission fluid flush & relearn), there's no trick to telling the computer something is different except the software, but this is more in depth than just clearing the codes, this is usually considered a calibration/reset procedure.

Regardless, glad you got the AWD working!
 

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Discussion Starter · #3 ·
Thanks for the reply! That makes sense, I drive the car for about a month with daily tire slippage trying to get up my driveway. I just couldn't believe that it wasn't working until resetting the codes after that long.
 
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