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BMW Fault Codes

I have a 2001 BMW 525i with a “service engine soon” light on. The car drives fine but I wanted to sort out the cause of this light. Local mechanic pulled up the codes, PO313 “misfire detected with low fuel”, PO171 “system too lean (bank 1)”, and PO174 “system too lean (bank 20”.

Does anyone know what the problem could be?

Try “Googling” Automotive Fault Codes and I bet a website should be listed. I tried this awhile ago and one website was free and another made ya pay a small fee for the code answers. Good Luck!

I got the quoted fault codes from a BMW manual. Problem is it really doesn’t tell you what the underlying problem is. To find that out you need to take it to a dealership, something I’m trying to avoid.

If you have a BMW manual it should have instructions for troubleshooting things like misfire or lean running. It’s usually a process of elimination. You may need some specialized tools and equipment to test certain components.

The dealer follows the diagnostic chart in the BMW service manual.

Could be a vacuum leak, look under the plastic cover over the valve cover, there was a problem with a large vacuum line in this area on the E-46 (3-series) in the year you mention. I don’t think you have to take the valve cover to get to it, but I just can’t remember.

I would look for:

Vacuum leak.
Cracked air tube.
Dirty Idle air control valve.
Bad throttle position sensor.
Fuel pressure regulator (I think it is on your fuel filter on this car, so now might be a good time for a new fuel filter)
Check the connection between the engine and the fuel pressure regulator.

Thanks to all!