P0175 Engine computer has reached its limit removing fuel on bank 2: the mixture is rich

System too rich, bank 2

Monitor

With normal running this is an emissions and fuel-economy fault you can drive on briefly while booking a diagnosis; a rich mixture shortens catalytic converter life, so don't leave it.

It gets more serious if:

  • Inspect soon: Inspect soon if the engine idles roughly, hesitates, stalls, misfires or pings under load; a mixture that far off stresses the catalytic converter and can leave you stranded.
  • Stop: Stop if the check engine light starts flashing: that means an active misfire hot enough to damage the catalytic converter. Pull over where nothing flammable is under the car and let it cool.

Source: how we rate severity

P0175 in short

P0175 means the engine computer is cutting fuel as far as it is allowed on bank 2 and the mixture is still rich. Common causes are a leaking injector, high fuel pressure, a stuck-open purge valve or a coolant sensor reading cold. Get it checked soon, especially if the engine idles roughly or stalls.

The upstream oxygen sensor reports whether the exhaust is rich or lean, and the computer adjusts fuel to keep it balanced. P0175 sets when the computer has been removing fuel up to its calibrated limit on bank 2 and the exhaust still reads rich. Bank 2 is the side of the engine without cylinder 1, so this code only appears on V-type and flat engines.

Either too much fuel is arriving or the engine is getting less air than the computer thinks. Too much fuel comes from a leaking injector, excessive fuel pressure or a purge valve feeding fuel vapour. A coolant sensor that reads cold, or an airflow or pressure sensor that reads high, tricks the computer into adding fuel.

Running rich wastes fuel, can foul spark plugs and oxygen sensors, and sends unburned fuel into the catalytic converter, which shortens its life. That is why P0175 is often worth fixing before a converter code that appears with it.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Leaking or stuck-open fuel injector on bank 2

    Common general cause
    Why it ranks here
    An injector that drips or sticks adds fuel the computer can't take away, forcing the trims negative. It is one of the classic rich causes and can also flood the converter.
    What would change this
    A fuel smell, a cylinder with a fouled black plug, or fuel pressure that bleeds down after shutdown raises this; injectors that hold pressure lower it.
    How to test the fuel injector

  2. Fuel pressure too high (faulty regulator or control)

    Common general cause
    Why it ranks here
    Too much pressure pushes more fuel through every injector. Saab's procedure measures fuel pressure early in the rich-code diagnosis.
    What would change this
    Pressure above specification on a gauge confirms it; pressure in specification rules it out.
    How to test the fuel pump

  3. EVAP purge valve stuck open, feeding fuel vapour at idle

    Common general cause
    Why it ranks here
    A purge valve that won't close pulls fuel vapour from the charcoal canister into the engine, especially after refuelling. Saab's procedure checks for a stuck purge solenoid.
    What would change this
    Trims that move back toward normal when the purge line is blocked confirm it; no change rules it out.
    How to test the evap canister purge valve

  4. Coolant temperature sensor reading too cold

    Common general cause
    Why it ranks here
    If the sensor tells the computer the engine is cold, it adds warm-up fuel the warm engine doesn't need.
    What would change this
    A coolant reading well below the real temperature on a warm engine raises this; a plausible reading rules it out.
    How to test the engine coolant temperature (ect) sensor

  5. Airflow (MAF) or manifold pressure (MAP) sensor reading high

    Possible — needs testing
    Why it ranks here
    A sensor that over-reports airflow or load makes the computer inject more fuel than needed. Which sensor matters depends on the engine.
    What would change this
    Airflow or pressure readings above known-good values for the engine raise this; normal readings lower it.
    How to test the mass airflow (maf) sensor

  6. Restricted air intake

    Possible — needs testing
    Why it ranks here
    Saab's service information describes this code as too little air or too much fuel; a badly blocked air filter or intake is the too-little-air side.
    What would change this
    A blocked filter or intake path raises this; a clean, open intake rules it out.

  7. Bank 2 upstream oxygen sensor reading falsely rich

    Possible — needs testing
    Why it ranks here
    A contaminated or failing sensor can report rich when the mixture is fine, so the computer pulls fuel it shouldn't. Ranked last because a good sensor usually reports a real rich condition.
    What would change this
    A sensor that stays rich during a controlled lean change, or a tip with heavy deposits, raises this; crisp response rules it out.
    How to test the oxygen (o2) sensor

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Record all codes and freeze-frame data, then watch fuel trims and the coolant temperature reading on a fully warm engine

    Low riskTool: scan tool with live data

    Warning:Keep hands, hair and loose clothing clear of the belts and fan while the engine runs, and never run the engine in a closed garage.

    • IfCoolant temperature reads far colder than the engine really is

      It meansThe computer thinks the engine is cold and is adding fuel.

      Points to: Coolant temperature sensor reading too cold

    • IfCoolant reading is plausible and trims are strongly negative

      It meansSomething is adding fuel or the computer is over-estimating air; check the purge valve first.

      Go to step 2

  2. At idle, briefly block or disconnect the EVAP purge line at the intake and watch the fuel trims

    Use cautionTool: scan tool; hose pinch tool

    Warning:Keep hands, hair and loose clothing clear of the belts and fan while the engine runs, and never run the engine in a closed garage.

  3. Inspect the air filter and intake for blockages, and compare the airflow (MAF) or manifold pressure (MAP) reading with known-good values for the engine

    Low riskTool: scan tool with live data

  4. Have fuel pressure measured, and check whether it holds or bleeds down after the engine is shut off

    Best left to a shopTool: fuel pressure gauge (shop)

    Warning:The fuel system is under pressure and gasoline is a fire risk. Fuel-pressure testing means opening the fuel system: relieve pressure first, no flames or sparks nearby, and leave it to a shop if you don't have the gauge and procedure for your engine.

  5. Test the bank 2 upstream oxygen sensor's response to a controlled lean change and inspect its tip

    Best left to a shopTool: scan tool with graphing (shop)

    Warning:Exhaust parts stay hot enough to burn skin long after the engine stops. Let the car cool for at least an hour, and never get under a car held up only by a jack.

Symptoms

  • Check engine light, often with worse fuel economy
  • Fuel smell or black smoke from the exhaust
  • Rough idle, hesitation or stalling Gets more serious: stop and have it checked.
  • Check engine light flashing, or the engine shakes and stumbles under load Gets more serious: stop and have it checked.

Compare with: Rough idle with the check engine light on, Check engine light came on after getting gas

How to fix

  1. Check that the air filter is not clogged and the intake duct is not blocked or collapsed.

  2. Note whether the code appears mainly after refuelling or at idle; that pattern points toward the EVAP purge valve and is worth telling your mechanic.

Parts and cost context

  • EVAP canister purge valve:Usually a modest part; confirm it is stuck open before replacing.
  • Engine coolant temperature (ECT) sensor:Inexpensive, but replace only if its reading disagrees with the real engine temperature.
  • Fuel injector:Leaking injectors are confirmed with pressure and balance tests; replacing them involves fuel-system work best left to a shop.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

  • 2010 · Equinox

    Supported by vehicle data

    On some 2010 GM models with direct injection (including Equinox), P0175 with P0172 and rough running led GM to the high-pressure fuel pump after diagnosis.

  • PI-0145Status unverified

    P0172 and P0175 with rough running: high-pressure fuel pump

    2010equinox · issued · NHTSA 10036504

    GM preliminary information for some 2010 models (including Equinox, Terrain, LaCrosse, CTS, SRX): with P0172 and P0175 and a rough-running engine, follow diagnosis and replace the high-pressure fuel pump.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P0172Engine computer has reached its limit removing fuel on bank 1: the mixture is rich

    Other bank Common general cause

    P0172 is the same rich test on the other bank of a V-type or flat engine. When both are stored, start with what both banks share, such as fuel pressure, the purge valve or the coolant sensor.

  • P0430Catalytic converter efficiency below the computer's limit (Bank 2)

    Primary / secondary Possible — needs testing

    Likely primary: P0175. A rich mixture overloads and overheats the catalytic converter and can make it fail its efficiency test. Fix P0175 first, then recheck the converter.

  • P0300Random or multiple-cylinder misfire detected

    Primary / secondary Possible — needs testing

    Likely primary: P0175. Saab's service information lists misfire among the possible symptoms of a rich code; fix the mixture before chasing ignition parts.

All Fuel trim (air-fuel mixture) codes

P0175 questions

Can I drive with P0175?

Briefly, if the engine runs normally. A rich mixture slowly damages the catalytic converter and fouls spark plugs and sensors, so book a diagnosis. If the engine stalls, misfires or the light flashes, stop driving it.

Why does P0175 show up after I fill the tank?

Refuelling loads the EVAP canister with vapour. If the purge valve is stuck open, that vapour floods into the engine at idle and drives the mixture rich.

Will a new oxygen sensor fix P0175?

Usually not. The sensor is normally reporting a real rich mixture. Replace it only if a test shows it reads falsely rich or responds slowly.

What is the difference between P0172 and P0175?

They are the same rich test on different banks. Bank 1 is the side of the engine with cylinder 1; bank 2 exists only on V-type and flat engines. If both are stored, look first for a cause both banks share, such as fuel pressure or the purge valve.

Can P0175 damage my catalytic converter?

Yes, over time. Unburned fuel overheats the converter and shortens its life, which is why a rich code should be fixed before a converter is replaced.

Sources and review

  1. Saab 9-3 (2008) WIS DTC P0172 00 (ME9): Long term fuel trim min value, air/fuel too rich — Saab Automobile (Saab WIS service information, hosted by Saab Club of North America)
  2. Bosch Oxygen Sensors consumer brochure — Robert Bosch LLC ,
  3. Saab 9-2X 2.5i (2005) WIS DTC P0172 System too rich (bank 1); P0171 uses the same procedure — Saab Automobile (Saab WIS service information, hosted by Saab Club of North America)
  4. General Motors bulletin PI-0145: P0172 and P0175 with rough running: high-pressure fuel pump — General Motors (filed with NHTSA) ,
  5. Final Regulation Order: 13 CCR §1968.2, Malfunction and Diagnostic System Requirements (OBD II) for 2004 and later passenger cars, light-duty trucks and medium-duty vehicles — California Air Resources Board
  6. 2026 Honda Pilot Owner's Manual: Indicator Coming On/Blinking (Malfunction Indicator Lamp) — American Honda Motor Co.
  7. P0420 Code: The Guide to Diagnosis and Fast Fixes — Identifix ,
  8. Bosch Oxygen Sensors trade brochure — Robert Bosch LLC ,
  9. A/F Sensors — DENSO Auto Parts
Last reviewed
Written by
Saurabh K.
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