Quote:
Originally posted by nbml430
Hello Folks,
I have a '99 ML430 that is displaying the 'Check Engine' light. I took it to a local motorsport shop and had the codes read, po170 and po173. I was told it means a bad air mass sensor. I bought my vehicle from CarMax and the MaxCare extended warrantee gave my local dealer such a run around that they suggested taking it to CarMax for repair. CarMax is telling me that those codes indicate a bad fuel pressure regulator. After searching the forums, the major of what I read would indicate a bad air mass sensor. What are the chances that CarMax is correct in that it's a faulty fuel pressure regulator? Anyone ever heard of this? Thanks for your help. -Norm
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The code P0170 and P0173 are adaptation codes. That means the controller has tried to repair a mixture problem and couldn't within the software parameters it was built with. The typical AMM problem causes the part load adaptation to go to 1.32 trying to repair a lack of load signal from the AMM. That mean it is adding 32% more fuel than original calibration because the car is way too lean. The diagnostician will know if the parameter is failing rich or lean by reading the adaptation values.
A fuel pressure regulator can cause the car to run rich or lean due to fuel pressure being out of spec. If spec is 40psi, then 60 will be 50% too much fuel (probably... may not be linear). Fuel pressure regulators usually fail by raising the pressure so one would expect numbers in the range of .68 (32% less fuel adaptation) as the controller tries to fix a rich mixture.
So the situation is simple for a knowledgable tech. Readapt to 1.00 and drive the car, if it relearns one way or the other one can simply read the fuel pressure (as simple as reading tire pressure on that model) and verify first if it is out of spec and second if it is out the same direction as the adaptation.
Deciding and proving the AMM isn't quite as easy as its output is dynamic and there isn't an exact this for that type measurement.
From your standpoint it should be easy. Let them put a fuel prressure regulator on it. They will be wrong and when in a week or two the light is back on you can get them to repair it right.
BTW after the AMM is replaced an exact confirmation is to be had by anyone knowledgable enough to look. The proof is that after ten miles or so of driving the thing is no loner having to adapt. It becomes cut and dried at this point.