P2097 The engine computer has had to take fuel away based on the downstream oxygen sensor because the exhaust after the catalytic converter reads rich on bank 1

Post-catalyst fuel trim too rich, bank 1

Monitor

If the engine runs normally, this is an emissions and fuel-control fault you can drive on briefly while booking a diagnosis. GM notes false P2097 codes on cars that run normally, but a real rich condition can foul plugs and harm the catalytic converter over time.

It gets more serious if:

  • 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

P2097 in short

P2097 means the oxygen sensor after the catalytic converter on bank 1 keeps reading rich, and the computer has reached its limit trying to correct it. Small exhaust leaks, a faulty rear sensor or heater, leaking injectors and software are common causes. It's usually drivable short-term; get it checked if it runs rough.

Most engines fine-tune fuel using two oxygen sensors per bank. The downstream sensor, after the catalytic converter, adds a slow correction called post-catalyst fuel trim.

P2097 sets when that correction has removed as much fuel as allowed and the rear sensor still reads rich. Saab's procedure only flags it after two driving cycles in a row with the fault.

GM's guidance splits it in two: if fuel trims show the engine is adding fuel, look at intake leaks and injectors; otherwise check the rear sensor heater and circuits and look for small exhaust leaks. GM and Mitsubishi also fixed false P2097 codes with software.

Most likely causes

  1. Small exhaust leak near the sensors

    Supported by vehicle data
    Why it ranks here
    GM's PIP5215 and PIP4964C point to small exhaust leaks, and Saab's procedure checks exhaust condition.
    What would change this
    Likelier if you hear ticking from the exhaust or soot marks show at a joint.

  2. Rear oxygen sensor, heater or circuit fault

    Supported by vehicle data
    Why it ranks here
    GM checks the rear sensor heater and circuits, and Saab checks the rear sensor voltage and harness.
    What would change this
    Likelier if the rear sensor reading is stuck high or responds slowly.
    How to test the oxygen (o2) sensor

  3. Leaking or unbalanced fuel injectors

    Supported by vehicle data
    Why it ranks here
    GM's PIP4964C calls for an injector balance test, and PIP5215 checks for restricted injectors.
    What would change this
    Likelier with a fuel smell, rough idle or rich codes.
    How to test the fuel injector

  4. Software (bulletin fix)

    Supported by vehicle data
    Why it ranks here
    GM (Volt) and Mitsubishi bulletins correct false P2097 with software.
    What would change this
    Likelier on a covered model that runs normally.
    How to test the engine control module (ecm / pcm)

  5. Evap purge valve, fuel pressure or coolant temperature sensor

    Possible — needs testing
    Why it ranks here
    Saab's procedure checks purge and pressure control valves, fuel pressure and the coolant temperature sensor.
    What would change this
    Likelier if fuel trims swing when the purge valve operates.
    How to test the evap canister purge valve

What to test first

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

  1. Read all codes and freeze-frame data, and check whether long-term fuel trims show the engine adding or removing fuel

    Low riskTool: OBD-II scan tool

  2. With the engine cold, inspect the exhaust between the converter and rear sensor, and check the rear sensor heater and wiring

    Use cautionTool: Flashlight, multimeter

    Warning:Exhaust parts get hot enough to burn; let the engine cool fully before touching sensors or pipes.

  3. Pressure-test the exhaust with an EVAP tester and soapy water, and run an injector balance test

    Best left to a shopTool: EVAP smoke/pressure tester, scan tool

    Warning:Fuel systems hold pressure with the engine off; follow the maker's procedure.

Symptoms

  • Check engine light
  • Usually no change in how the car drives
  • Fuel smell or poor fuel economy
  • Misfire or flashing check engine light Gets more serious: stop and have it checked.

Compare with: Rough idle with the check engine light on

How to fix

  1. Ask a dealer to check your VIN for software bulletins; GM, Mitsubishi and Subaru have published bulletins for P2097.

  2. Look under the car for obvious exhaust damage near the rear oxygen sensor and get it repaired.

Parts and cost context

  • Oxygen (O2) sensor:Test the rear sensor and look for exhaust leaks before replacing it. Labour varies; get a quote.

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

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

  • 2013 · Malibu

    Supported by vehicle data

    Diagnostic tips for intermittent P2097: fuel trims, rear sensor heater and small exhaust leaks. Whether the bulletin is still current is not verified.

  • 2004–2014 · Equinox

    Supported by vehicle data

    Injector balance test and small exhaust leaks for P2097/P2099; covers many GM models. Whether the bulletin is still current is not verified.

  • 2016–2017 · Volt

    Supported by vehicle data

    False P2097 on a car that runs normally; inverter module reprogram. Whether the bulletin is still current is not verified.

  • PIP5215Status unverified

    Intermittent P2097 diagnostic tips

    2013malibu · issued · NHTSA 10112148

    For intermittent P2097, check freeze-frame fuel trims: if the computer is adding fuel, check for an aftermarket air filter, intake leaks and restricted injectors; otherwise check the rear oxygen sensor heater and circuits and look for exhaust leaks using an EVAP tester and soapy water.

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

  • PIP4964CStatus unverified

    P2097/P2099 diagnosis: injector balance and small exhaust leaks

    2004–2014equinox, traverse, camaro · issued · NHTSA 10111995

    Preliminary information for P2097/P2099 pointing to an injector balance test and small exhaust leaks. Covers many Buick, Cadillac, Chevrolet, GMC, Pontiac and Saturn models.

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

  • GCUS-3-842Status unverified

    False P2097; reprogram drive motor power inverter module

    2016–2017volt · issued · NHTSA 10113379

    P2097 can set falsely while the car runs normally; the drive motor power inverter module is reprogrammed.

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

Mitsubishi

  • TSB-15-13-002Status unverified

    False P2097: software, plus sensor replacement on some

    2011–2014lancer, outlander, outlander sport · issued · NHTSA 10098762

    False P2097 is corrected with software, with a sensor replacement on some 2011-2013 vehicles.

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

Subaru

  • 2015–2025 · Outback

    Supported by vehicle data

    Subaru issued a specific diagnostic procedure for P2097. Whether the bulletin is still current is not verified.

  • 18-228-25Status unverified

    Diagnostic procedures for P2096/P2097

    2015–2025outback, forester, crosstrek, impreza, ascent · issued · NHTSA 11025790

    Announces diagnostic procedures for P2096 and P2097.

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

  • P2096The engine computer has had to add fuel based on the downstream oxygen sensor because the exhaust after the catalytic converter reads lean on bank 1

    Same system Supported by vehicle data

    P2096 is the lean-side version of the same post-catalyst fuel trim check; Subaru's bulletin covers both.

All Fuel trim (air-fuel mixture) codes

Sources and review

  1. Saab 9-2X (2005) 2.5i DTC P2097 Post Catalyst Fuel Trim System Too Rich Bank 1 — Saab Automobile (WIS)
  2. GM GCUS-3-842: false P2097, drive motor inverter reprogram (Volt) — General Motors / NHTSA ,
  3. Subaru 18-228-25: diagnostic procedures for P2096/P2097 — Subaru ,
  4. 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
  5. 2026 Honda Pilot Owner's Manual: Indicator Coming On/Blinking (Malfunction Indicator Lamp) — American Honda Motor Co.
  6. GM PIP5215: intermittent P2097 (Malibu) — General Motors / NHTSA ,
  7. GM PIP4964C: P2097/P2099 post-catalyst fuel trim too rich — General Motors / NHTSA ,
  8. Mitsubishi TSB-15-13-002: false P2097 (Lancer, Outlander) — Mitsubishi Motors North America / NHTSA ,
Last reviewed
Written by
Saurabh K.
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