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Code P0174 "System Too Lean"


Supporting Member
Sep 2, 2013
Monument Colorado
My XLR/V(s)
2006 Gold Mist XLR & 79' Eldorado Convert
Sharing information here. My check engine light kept coming on. Code P0174 "System Too Lean". I searched everywhere and tested everything. There were no vacuum leaks. None! The mass air sensor tested good. O2 sensors (4 ea.) all tested good. Gas cap tested good. Usually what causes a 'too lean code' is often, but not always, a vacuum leak. Outside air invading the fuel mixture somewhere. In short, I had ruled out every possible mechanical thing I could find that would set this code? To no avail. It kept coming on.

Finally took it to my Cadillac Dealer. They hooked up their Tech II Code Reader to The ECM. Found that the original XLR Settings had never been "re-flashed' (re-set) and their was a Service Bulletin on it at the dealership. They re-set The ECM using their Tech II and no more P0174 Code and no more check engine light on. Yea! :thumbsup Cost? $168.00. --- FYI, they also checked everything I had previously checked, and like me, found no issues with those items.


Jul 6, 2020
Temple, TX
Great post! I’ve been on the same hunt looking for a vacuum leak. I have P0171 and P0174. The read out from Advanced Auto said the ECM needed to be flashed to new specs. I couldn’t believe it because everyone says these codes are vacuum related. Can’t avoid the dealer on this one. Thanks again!

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