P0172: System too rich (bank 1)
The engine computer sees too much fuel or too little air and is removing fuel to compensate.
Updated
What P0172 means
The engine computer corrects the amount of fuel it injects, based on an oxygen sensor in the exhaust. That correction is called fuel trim.
When it has to take away more fuel than its limit allows, it stores P0172: the engine gets too much fuel or too little air. It’s the opposite of P0171 (too lean), with different causes.
Read My Car shows short and long term fuel trim under Live data, if your car reports them. Negative numbers mean the computer is taking fuel away.
P0175: the same fault on bank 2
P0175 is the same fault on bank 2, the side without cylinder 1, which only V and flat engines have. When P0172 and P0175 are stored together, look for a cause both banks share, such as the fuel pressure, the air flow sensor or the air filter.
P0175: System too rich (bank 2)
Can I keep driving?
Check soon
Probably OK to drive short-term, but have it checked soon. Fuel use or emissions may be worse.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
Over time, a rich mixture can foul the spark plugs and overheat the catalytic converter, so don’t leave it for long.
Symptoms
- Higher fuel use.
- A smell of fuel from the exhaust, or black smoke on some cars.
- A rough idle, or misfire codes stored as well.
Common causes
- Leaking injector. Fuel drips into the cylinder on top of what the computer meters.
- Faulty air flow (MAF) or oxygen sensor. An air flow sensor that over-reads the air makes the computer inject more fuel than the engine needs. An oxygen sensor that wrongly reports a rich mixture can also set this code, by making the computer take fuel away until it reaches its limit.
- Fuel pressure too high. For example from a faulty fuel pressure regulator, so every injection delivers too much.
- Clogged air filter. Less air for the same amount of fuel. Easy to check, so worth ruling out first.
Typical fixes
- Check the air filter and the intake for blockages.
- Have the air flow sensor and oxygen sensor readings checked with live data.
- Have the fuel pressure tested, and the injectors checked for leaks.
- Clear the codes after the repair and check in live data that fuel trim moves back towards zero.
Questions
Can I drive with P0172?
Probably for a short time, but have it checked soon: fuel use or emissions may be worse. If misfire codes appear too, avoid hard driving.
What is the difference between P0172 and P0175?
The same fault on different banks. P0172 is bank 1, the side with cylinder 1; P0175 is bank 2 of a V or flat engine.