P2178: Mixture too rich away from idle (bank 1)
The ECU sees bank 1 getting too much fuel when driving or revving. Common culprits are injectors, fuel pressure or the air flow sensor.
| Code | P2178 |
|---|---|
| System | Engine and transmission |
| Group | P21xx, Throttle, injection and emissions |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P2178 means
Above idle, the ECU has to keep taking fuel away on bank 1 to hold the right mixture. When that correction reaches its limit and there is still too much fuel, it stores this code. Bank 1 is the side of the engine that has cylinder 1.
Most common causes
- Dirty or faulty mass air flow sensor reading less air than is really going in
- An injector that drips or does not close fully
- Fuel pressure too high because of a faulty regulator
- Upstream oxygen sensor giving a false reading
- Evaporative purge valve (fuel vapour canister) stuck open
- Coolant temperature sensor that always reads cold
Symptoms
- Engine warning light on
- Higher fuel consumption than usual
- Fuel smell from the exhaust
- Hesitation or flat response when accelerating
Can you drive with P2178?
With care The car can be driven, but running rich burns more fuel and can damage the catalytic converter over time. Get it checked soon.
Open the bonnetthe in-depth explanation
How to check it
Watch bank 1 long term fuel trim (LTFT) live at around 2,500 rpm: a strongly negative figure means the ECU is pulling a lot of fuel. Note the air flow reading too, it helps the workshop.
How to read and clear P2178 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P2178 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P2174 The throttle suddenly lets through less air than expected
- P2175 The throttle control system detects airflow that is too low
- P2176 The throttle actuator control system idle position needs its learning procedure
- P2177 System too lean off idle (bank 1)
- P2179 Mixture too lean away from idle (bank 2)
- P217A The fuel injector unit G power supply voltage has a broken or disconnected wire
- P217B The fuel injector unit G power supply voltage is below normal
- P217C The fuel injector unit G power supply voltage is above normal
- P2100 Throttle actuator A control motor circuit open
- P2101 Throttle actuator A control motor circuit range or performance
- P2102 Throttle actuator A control motor circuit low
- P2104 Throttle control system: forced idle
What does code P2178 mean?
Above idle, the ECU has to keep taking fuel away on bank 1 to hold the right mixture. When that correction reaches its limit and there is still too much fuel, it stores this code. Bank 1 is the side of the engine that has cylinder 1.
Can you drive with P2178?
The car can be driven, but running rich burns more fuel and can damage the catalytic converter over time. Get it checked soon.
How do you clear P2178?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P2178 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
