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Thread: System Banks 1 and 2 too rich (P0172 & P0175)

  1. #1
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    System Banks 1 and 2 too rich (P0172 & P0175)

    My car was displaying the SES light so I ran it for codes and it spat out P0172 and P0175. One of the symptoms I've noticed that's consistent with these is that the car almost stalls when I push in the clutch. What's my best course of action?
    -Dimitri; 19

    98 Dakar Yellow M3
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  2. #2
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    Look for vacuum leaks and check MAF.

    t.

  3. #3
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    Quote Originally Posted by tkundhi View Post
    Look for vacuum leaks and check MAF.

    t.
    What do I look for when I check the maf?
    -Dimitri; 19

    98 Dakar Yellow M3
    Recaro - Ground Control - Macht Schnell - AP - Mashaw - UUC - Schroth - Apex - TMS

  4. #4
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    Start your car, unplug the MAF, does it run better or worse? If it runs better with MAF unplugged but goes back to crappy when you plug the MAF wire back on there, that's your suspected culprit. Try using some MAF cleaner first, you may get lucky that that is all it needs.

    However, 172 & 175 are classic torn boot codes, I'm suspecting that. Start the car, let it run, in a one after the other process, spray carb cleaner around lower boot area, then the upper to lower boot connector, then around the F connector, along sides of upper boot, finally at the upper boot to MAF connection. Anywhere along this process, if your idle rises (from the vacuum leak sucking in the rich carb cleaner), then you've found your vacuum leak.

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  6. #6
    Quote Originally Posted by BCS_ZHP View Post
    Start your car, unplug the MAF, does it run better or worse? If it runs better with MAF unplugged but goes back to crappy when you plug the MAF wire back on there, that's your suspected culprit. Try using some MAF cleaner first, you may get lucky that that is all it needs.

    However, 172 & 175 are classic torn boot codes, I'm suspecting that. Start the car, let it run, in a one after the other process, spray carb cleaner around lower boot area, then the upper to lower boot connector, then around the F connector, along sides of upper boot, finally at the upper boot to MAF connection. Anywhere along this process, if your idle rises (from the vacuum leak sucking in the rich carb cleaner), then you've found your vacuum leak.
    Guys, the 0172 and 0175 are system RICH codes. The codes for torn boots or vacuum leaks are 0171 and 0173. If it was a vacuum problem, UN-metered air would be getting into the cylinders and that causes a LEAN condition.

    OP, you are running rich, meaning too much fuel. I have those codes because of my headers. Is your exhaust stock? If it is then you will likely have an issue with your 02 sensors. You need a scanner that can read the voltage real time on your 02 sensors. It could also be a bad fuel pressure regulator which is integral in the fuel filter. Then check your plugs too.

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  7. #7
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    Smolck, yes these are rich codes but a tiny vacuum leak can cause them. Not a massive leak, which should immediately throw a lean code. That is why I didn't state look for torn intake boots. I agree with you that torn intake boots should cause lean codes as there is no way for the system to compensate for all the extra unmetered air.

    Fuel pressure regulator is also a possible causes for P0172 & P 0175. But I would start with the simple stuff and then do further diagnostics as you suggest. Find out what the O2 readings are, measure fuel pressure, etc...

    t.

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