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Dave Nova
Dave Nova, GMC Technician
Category: GMC
Satisfied Customers: 19452
Experience:  ASE Master Certification. GM World Class Certification
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I have a 2001 GMC Yukon Denali and this morning it began

Customer Question

Hello My name is***** have a 2001 GMC Yukon Denali and this morning it began driving horribly. The CEL flashed and it stumbled and could barely maintain 50 MPH. I stopped at Autozone to have the CEL checked. It was throwing codes P0171, P0174, P0430, P0300 and P0706.
JA: Thanks. Can you give me any more details about your issue?
Customer: I know I attempted to add oil to it a couple days ago and spilled quite a bit on my attempt. The engine stumbles and feels like it wants to stall. Going up hills was a major struggle.
JA: OK got it. Last thing — GMC Mechanics generally expect a deposit of about $18 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 1 year ago.
Category: GMC
Customer: replied 1 year ago.
Its also throwing code P1810 and P1125. Please help...
Expert:  Dave Nova replied 1 year ago.

Did you clear the codes to see which ones would return?

Customer: replied 1 year ago.
No, took it back home and had to take my other vehicle.
Expert:  Dave Nova replied 1 year ago.

Did the engine feel like it was misfiring, or was it just a general loss of power?

Customer: replied 1 year ago.
It was misfiring. The truck struggled going up hills and would not travel faster than 50mph.
Expert:  Dave Nova replied 1 year ago.

With the codes you have, p0171 and P0174 are lean codes and P0300 is a misfire code. Sounds like the engine is starving for fuel. If you have not replaced the fuel filter in a while, I'd start there. Beyond that, testing fuel pressure will reveal whether the fuel pump needs to be replaced. You should have 60-66 psi fuel pressure with the key on, engine off. If the fuel pressure is lower than specified, the fuel pump should be replaced.