P0171 Gmc -

Question

My 2003 Yukon XL was showing P0171, 0172 and 0174. I changed the Mass flow sensor and the code changed to P0171 and P0174. What else should I look at?

Answer 1

P0171 System too lean Bank 1

P0174 System too lean Bank 2

Lean system on both side of the Bank, look for a vacuum leak especially at or along the intake manifold gasket by use of carburetor or brake cleaner, and even at the brake master cylinder and this includes the brake booster hose, If no vacuum are found a fuel pressure test has to be performed