Is there a BMW Error code P0470? '99 BMW 528i with 104,000 mi has intermittent "Service Engine Soon" light. On advice of dealer, had secondary air pump & valve replaced. Dealer also said spark plugs needed to be replaced, which I did myself ($36 parts & my labor vs. $312 dealer). Light came back and has been intermittent on a few days, off a few days. Came back on, and AutoZone printout is for error code P0470. This isn't listed in my Bentley manual for 52TU/54 engine. As an SAE code, it seems to point (at least for Fords) to an exhaust pressure (EP) sensor, possibly due to a short circuit on the signal return...I have no idea where this is, or how to DIY...is it time to go back to the dealer? O2 sensors were replaced about 2 yrs ago.