System Too Rich (Bank 2)
What it means
The engine computer is removing more fuel than normal on bank 2 to make up for a rich mixture, and has reached its maximum correction. It appears on engines with two banks; if P0172 appears with it, the cause is usually shared, such as fuel pressure or the airflow sensor, and if it appears alone, suspect an injector on bank 2.
Symptoms4
- Check engine light on.
- Higher fuel consumption.
- Fuel smell or black smoke from the exhaust.
- Uneven idle or misfires on bank 2 cylinders.
Possible causes6
- Leaking injector on bank 2.
- High fuel pressure from a failed regulator.
- MAF sensor over-reading.
- EVAP purge valve stuck open.
- Coolant temperature sensor falsely reading cold.
- Fuel diluting the engine oil.
How to diagnose5
- Compare fuel trims between banks; if only bank 2 is strongly negative, check its injectors.
- Watch the misfire counters for bank 2 cylinders, since a leaking injector can flood its cylinder.
- Measure fuel pressure and how well the system holds pressure after shutdown.
- Test the EVAP purge valve and the coolant temperature sensor.
- Inspect the bank 2 spark plugs; a wet or black plug points to the affected cylinder.
How to fix5
- Replace a stuck purge valve or a faulty temperature sensor if proven bad.
- Clean or replace the MAF sensor.
- Repair the fuel pressure regulator if pressure is high.
- Replace the leaking injector and fouled plugs, and change the oil if it is diluted with fuel.
- Clear the codes and confirm the fuel trims return to normal.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
A purge valve or MAF cleaning are low-cost fixes; the cost rises for injectors or a pressure regulator, especially on engines where bank 2 injectors are hard to reach.
Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026
Frequently asked questions
Can this code damage the catalytic converter?
Yes. Extra fuel burns inside the converter and overheats it, and if it lasts long it can destroy it and set a code such as P0430.
How do I find the leaking injector?
By checking the bank 2 spark plugs and misfire counters, then having the injectors tested at a workshop for leakage and spray balance.
This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.
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