Skip the auto shop - Our mechanics make house calls

P2178 OBD-II Trouble Code: System Too Rich Off Idle Bank 1

Check Engine Light

What the P2178 code means?

P2178 is an OBD-II generic code for the engine control module (ECM) detecting the fuel control has reached it specification limits for short and long fuel trim when the engine is just off idle with light acceleration on bank 1.

What causes the P2178 code?

  • The ECM controls the fuel using a closed loop feedback system. If the system is trying to lean the fuel mixture and the O2 sensor keeps saying the system is too rich on bank one. If the system reaches 25% toward leaning out the mixture and the O2 sensor still indicates the system is rich then the check engine light is turned on and the code P2178 is set.

  • The intake air system may be clogged or the throttle body is dirty.

  • A misfire on bank one cylinders.

  • The O2 sensor is deteriorated and cannot sense the proper O2 levels.

What are the symptoms of the P2178 code?

  • The Check Engine light will be illuminated and the code is set in ECM memory as a fault.

  • The engine will run rich on bank one and the engine may run rough and misfire.

  • The engine may hesitate on acceleration.

How does a mechanic diagnose the P2178 code?

  • Scans for codes and documents the code in the ECM and looks at the freeze frame data for failure.

  • Checks for any misfire codes and corrects the misfire code first.

  • Removes all spark plugs on bank one of the engine and checks to see what plug is running rich.

  • Checks the intake and throttle body for dirty filters or throttle body.

Common mistakes when diagnosing the P2178 code?

  • Clearing ECM memory codes before checking the freeze frame data for the main failure problem, so the failure may be duplicated and repaired

  • Failing to clear the ECM codes after the codes are fixed so the ECM will enable the system to normal again

  • Failing to correct any engine misfire codes first before diagnosing code P2178.

How serious is the P2178 code?

Code P2178 is a code indicating the engine is running rich on only one side and this rich condition can cause the engine to misfire or the misfire is the cause of the code P2178.

What repairs can fix the P2178 code?

Additional comments for consideration regarding the P2178 code

Code P2178 is for a rich running engine on bank one and the most common problem is the engine has a misfiring cylinder on that bank or all the plugs are worn and not burning the fuel mixture good enough on that bank.

Need help with a P2178 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

The Traveler’s Guide to Driving in Malaysia
CraigBurrows / Shutterstock.com Malaysia is a popular destination for many tourists today. The country has amazing sights and attractions that you will want to explore....
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...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...


Related questions

Q: Car is misfiring and has a lack of power

It is very difficult to definitively say what the issue is. Have you had the vehicle scanned for diagnostic troubleshooting codes? If not, you should start there. Due to your vehicle being pre-1996, the method of receiving codes will be...

Q: Key not recognized by truck - 2006 Mitsubishi Raider

Hello. I would usually start by checking the battery and the connections at the battery. If there is low voltage in the system, then this will occur. If the battery and connections are fine, then the issue is either in...

Q: P2178 and P115D codes are showing up on a scanner. Could both be related to the MAF sensor?

Hi there. The code P115D is for the mass air flow sensor (MAF). It says that the sensor has an offset signal. The code P2178 says that bank 1 is too rich. This means that the engine is running too...