Skip the auto shop - Our mechanics make house calls

Q: My truck is giving codes P0171 & P0174

asked by on

Last week my check engine light came on. I have a Harbor Freight OBD 2 code reader and got the codes P0102/P0171/P0174 on the reader. P0102 was the M.A.F. sensor and was replaced.Erased the codes and test drove approx 30 miles and C.E.L. came back on.Rechecked the codes and P0102 is gone. P0171 & 174(lean bank 1 & 2) keep coming up. Smoke test performed with plenum on & no vacuum leaks. Removed plenum and duct taped glove to throttle body and cut a finger off a glove to place over the hose from valve cover to plenum. Rechecked with some - no leaks. Cold started engine and sprayed carb spray to see if rpm's would rise. Nothing. Visual inspection found nothing as well. Fuel pressure check revealed 35psi with key on,engine not running. With engine running 35-38psi. After turning engine off - approx 20-25 minutes for gauge to drop to zero. Fuel pump or fuel pressure regulator.?I don;t have a live data OBD tool to check fuel trims. Also hard to start after short drive. Have to use starter spray to start and runs fine.

My car has 88900 miles.
My car has an automatic transmission.

Hi there. If the engine is running lean, then there could be a plugged fuel filter or a faulty fuel pump with loss of pressure. If the pressure is dropping after 20 to 25 minutes, then there could be a problem with the fuel pump check valve. When the pressure is at 0, having a pressure gauge on the fuel rail, check for the pressure to increase as the fuel pump is turned on when the key is turned on.

If the pressure takes some time before it stops, then the check valve in the pump is sticking open. This means the fuel pump should be replaced. If the fuel pressure is measured very quickly, then replace the fuel pressure regulator on the fuel rail. If you need further assistance troubleshooting your vehicle, then seek out a certified technician, such as one from YourMechanic, who can come to your location to determine why the engine is running at a lean condition and suggest the necessary repairs.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Fuel pump

Hi there: Is it possible - yes; would I recommend doing this - never. Although the fuel pump is typically located on the top of the fuel cell below the rear seat, cutting a hole in the floor board would...

Q: My Lincoln ls 2004 has 9 codes at onece

Hi there. Your vehicle is in a lean mixture state. The fuel system is not supplying enough fuel to the engine. Check the fuel pump to see if its working by putting on a fuel pressure hose on the fuel...

Q: My truck will turn over but wont start. Its making a clicking noise and then shuts off, what should i do to fix it?

Hi there. Check the fuel pump relay and see if the relay has failed. If the relay is working fine, then check the fuel pump and see if its coming on when you turn on the key. If you are...

Related articles

P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...