P0172: System running too rich (bank 1)
Bank 1 is getting more fuel than it needs. The usual suspects are a sensor misreading the incoming air or an injector that leaks.
| Code | P0172 |
|---|---|
| System | Engine and transmission |
| Group | P01xx, Air and fuel metering |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0172 means
The ECU keeps adjusting the air and fuel mix based on the oxygen sensor. When it has to take fuel away beyond its limit and the mixture is still rich, it stores this code. Inline engines only have bank 1, so the whole engine is affected.
Most common causes
- Very dirty or blocked air filter
- Dirty or faulty mass air flow (MAF) sensor reading less air than there really is
- Leaking injector that does not close fully
- Fuel pressure too high because of a faulty pressure regulator
- Coolant temperature sensor reporting a cold engine when it is warm
- Slow or failing upstream oxygen sensor
Symptoms
- Engine warning light on
- Higher fuel consumption than usual
- Smell of petrol from the exhaust or black smoke
- Rough idle or hesitation when accelerating
Can you drive with P0172?
With care You can keep driving, but the extra fuel pushes up consumption and over time can overheat and ruin the catalytic converter. Get it looked at soon.
Open the bonnetthe in-depth explanation
How to check it
Check the live long term fuel trim (LTFT) for bank 1: a large negative value means the ECU is pulling fuel and still cannot fix it. Also make sure the coolant temperature shown on the reader is realistic once the engine is warm.
How to read and clear P0172 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 P0172 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
- P016E The closed loop fuel pressure control in the limit pressure gives a higher
- P016F The closed loop fuel pressure control in the limit pressure gives a lower
- P0170 Fuel trim out of limits (bank 1)
- P0171 Mixture too lean (bank 1)
- P0173 Fuel trim malfunction (bank 2)
- P0174 System running too lean (bank 2)
- P0175 System running too rich (bank 2)
- P0177 The fuel composition sensor signal is out of range or its performance is
- P0100 Mass or volume air flow sensor circuit fault
- P0101 Air flow sensor range or performance problem
- P0102 Air flow sensor circuit low input
- P0103 Air flow sensor circuit high input
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: Misfires, catalyst and lambda sensors.
What does code P0172 mean?
The ECU keeps adjusting the air and fuel mix based on the oxygen sensor. When it has to take fuel away beyond its limit and the mixture is still rich, it stores this code. Inline engines only have bank 1, so the whole engine is affected.
Can you drive with P0172?
You can keep driving, but the extra fuel pushes up consumption and over time can overheat and ruin the catalytic converter. Get it looked at soon.
How do you clear P0172?
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, P0172 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.
