Skip the auto shop - Our mechanics make house calls

Q: Codes showing: P0171, P0420, P0174

asked by on

"We have a minivan and it's showing several codes: P0171 - bank 1-combustion too lean, P0420 - catalyst eff. too low, P0174 - combustion to low What do these things mean. I'm not auto savvy and need to understand before seeing a mechanic."

A: Hello. These diagnostic trouble codes are a...

Hello. These diagnostic trouble codes are an indication that there could be a problem with the oxygen sensor or that there is a vacuum leak. It is possible that the vacuum leak is located in the intake manifold. These codes could also simply be the result of a loose hose. I would suggest that you have a certified technician, like one from YourMechanic, come out and complete an inspection to determine why your check engine light is on.

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・Save up to 30%

Get a quote

What others are asking

Q: Bottom right radiator hose will not go into new radiator

Get a transmission line disconnect tool or pop the clip out with a small pick tool and reinstall it. The 'jiffy-tite' connectors and manufacturers of radiators will make the adapter fittings different sizes which could be why you are experiencing...

Q: Very hard to start vehicle

Hello. This code is also related to the catalytic converter not working properly. This can also happen when the ground wires connected to the O2 sensors are not properly hooked up causing them to send erroneous info to the computer....

Q: i have 3 code on my car P0431, P0174, P0305

Noise in exhaust systems occurs due to leaks as well as internal failure of the baffles in the muffler or resonator. So, just because there are no leaks, doesn't mean the exhaust system will be noise free. An [engine/exhaust noise...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
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...