codes were P0171 and P0174?

2004 FORD EXPEDITION

152,000 MILES • 6 CYL • 2WD • AUTOMATIC

GFREDERIQUE

MEMBER
1 POST

my service engine soon light came on and the error codes were P0171 and P0174 stating probable causes "oxygen sensor defective, ignition misfire, fuel injector problem, engine mechanical condition". Now my truck is starting to shake bad while siting at a light in drive position and shakes while backing up, and it acts like it wants to shut off and a couple of times the tachometer started to go up and down. What do you think is the issue?

Oct 26, 2010 at 7:31 AM

DANNY L

✓Experienced Mechanic
5,648 POSTS

Hello, I'm Danny.

Those 2 code are showing that both bank 1 and bank 2 are too lean. This is usually caused by a vacuum leak or some other type of air leak allowing excessive unmetered air into the engine. Here is a tutorial showing how to check for a vacuum leak:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

I've attached below picture diagnostic steps for your vehicle. Hope this helps and thanks for using 2CarPros.

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