P0175 means the engine control module's long-term fuel trim for bank 2 reached its negative limit: it removed as much fuel as its calibration allows and the bank 2 oxygen sensor still reported a rich mixture. P0172 is the same fault on bank 1; P0171 and P0174 are the lean versions. Bank 2 is the cylinder bank without cylinder 1. One bank rich with the other normal is the diagnostic starting point.
Severity: moderate. Can you keep driving? For a short time. A rich bank fouls spark plugs, washes oil from cylinder walls and overheats the catalytic converter on that side. Expect black smoke, a fuel smell, poor economy and possibly misfires. Have it looked at within days.
What the bulletins say
- Ford F-150 5.0 L flex fuel, 2018 to 2020 (special service message 48573): P0172, P0173, P0174 and P0175 together, caused by incorrect flex fuel learning, which Ford attributes to customer refueling habits or a stuck-open EVAP purge valve. The engine estimates ethanol content from fuel trim after a refuel; a purge valve dumping vapor during that learn, or small top-offs with different fuel, corrupts the estimate and both banks go rich.
- Ford F-150 2.7 L EcoBoost, 2018, built on or before 12 July 2018 (TSB 18-2310): P0175 among misfire, lean and rich codes, corrected by replacing the six high-pressure direct injectors with clips and tubes.
- GM V6 and V8 engines, 2014 to 2020 (bulletin 20-NA-098): guidelines for fuel injector replacement when P0171, P0172, P0174, P0175 and the misfire codes set, so that technicians confirm an injector fault before replacing a set.
Two of the three are injectors; the third is a learning strategy fooled by a purge valve. None is the oxygen sensor first.
Causes, in the order they are found
A leaking or stuck-open injector on bank 2, delivering more fuel than commanded.
A purge valve stuck open feeding fuel vapor into the manifold, which on a V engine affects the bank nearest the purge port more; combined with a flex fuel learn on Ford's 5.0 L, both banks.
A bank 2 upstream oxygen sensor biased rich, or contaminated, reporting rich when the mixture is not.
Fuel pressure too high from a failed regulator, usually both banks rich.
An airflow sensor reading high, usually both banks.
A restricted exhaust or a failing catalyst on bank 2 that affects the sensor's environment.
An engine mechanical fault on that bank, such as a valve or ring problem, with misfire codes.
The module, last.
A diagnostic order
- Compare bank 1 and bank 2 trims at idle and cruise. Only bank 2 rich means that bank's injectors, sensor or exhaust; both rich means fuel pressure, airflow, purge or a flex fuel learn.
- On a flex fuel vehicle, check the ethanol estimate against the fuel actually used, and test the purge valve for leakage with vacuum; Ford's 5.0 L case lives here.
- Check fuel pressure against specification, key on and running.
- Test bank 2 injectors: a balance test on the scan tool, or a leak-down test on direct-injection engines.
- Check the bank 2 upstream oxygen sensor for response and bias by comparing with bank 1 and with a propane or vacuum test.
- Look for misfire codes on bank 2 cylinders and check compression if present.
- Repair the cause, clear the trims and the code, and verify that trims return to near zero on both banks through a drive. Let the readiness monitors complete before an inspection.
Frequently asked questions
Can I drive with a P0175 code?
For a short time. A rich bank fouls plugs, dilutes oil and can overheat the catalytic converter on that side. Get it diagnosed within days, and stop if the engine misfires badly or the check engine light flashes.
Why is only bank 2 rich?
Because the fault is on that bank: an injector delivering too much fuel, an oxygen sensor reporting rich when it is not, or an exhaust or engine problem on that side. Both banks rich would point at fuel pressure, airflow, the purge valve or, on flex fuel engines, the ethanol estimate.
Is P0175 the oxygen sensor?
Sometimes, but on the vehicles with bulletins for this code the causes were injectors (Ford 2.7 L, GM V6 and V8) and a flex fuel learning error caused by a purge valve or refueling habits (Ford 5.0 L). Test the injectors and the purge valve before replacing a sensor.
How much does it cost to fix P0175?
A purge valve is an inexpensive part. An oxygen sensor is moderate. Injectors range from moderate on port injection to major on direct injection, which is why GM's guidelines require confirming an injector fault before replacing a set.
Related codes
- P0172: system too rich bank 1. P0171 / P0174: system too lean; see P0171 and vacuum leaks.
- P0441 / P0496: purge flow codes, involved in Ford's flex fuel case.
- P0300 to P0308: misfires, listed with P0175 in Ford's and GM's bulletins; see P0300 misfire codes.
- P0151 to P0155: bank 2 sensor 1 signal circuit.
The code number itself tells you the family and the domain; how to read an OBD2 code number explains what each character means.