P2178
System Too Rich Off Idle Bank 1
Bank 1 fuel trim shows a strong rich correction during off-idle operation. The ECU is forced to subtract fuel to keep the mixture near stoichiometric.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Increased fuel consumption
- Black smoke from exhaust on acceleration
- Smell of unburned fuel, fouled spark plugs
Common causes
Ordered by how often each turns out to be the cause.
- Leaking fuel injectorCommon
- Excessive fuel pressurePossible
- Stuck-open purge valvePossible
Parts involved
- Fuel Pressure Regulator
- Fuel Injector
- Mass Air Flow Sensor
- EVAP Purge Valve
P2178 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.