P2099 The engine computer sees a rich mixture on bank 2 from the sensor behind the catalytic converter and the fuel trim cannot correct it

Post catalyst fuel trim system too rich, bank 2

Monitor

This is a fuel-trim and emissions fault. The sources describe higher fuel use, rough idle and a failed emissions test rather than an immediate danger, so you can usually drive while you book a check.

It gets more serious if:

  • Inspect soon: Inspect soon if the check engine light flashes, you smell fuel, or the engine runs rough or loses power. A rich mixture and a misfire can overheat and damage the catalytic converter.

Source: how we rate severity

P2099 in short

P2099 means the computer reads a rich mixture on bank 2 from the sensor behind the catalytic converter and cannot trim it out. A faulty downstream oxygen sensor, its wiring, a failing converter or an exhaust leak are the usual causes. It is usually drivable, but get it checked soon if the engine runs rough.

The computer watches the oxygen sensor behind the catalytic converter on bank 2 and compares it with what the converter should be passing. If that sensor keeps reporting a rich exhaust, the computer applies a correction and sets P2099 when the correction runs out.

The sensor can be telling the truth or can be at fault. A downstream oxygen sensor with a bad signal, damaged wiring or an exhaust leak ahead of it can all look like a rich mixture. A worn converter can also let unburned fuel through.

GM has told technicians to run an injector balance test and look for a small exhaust leak when P2097 or P2099 sets. Stellantis (Chrysler, Dodge, Jeep, Ram) and Nissan have issued software updates for the same pair of codes on some trucks.

Most likely causes

  1. Downstream oxygen sensor or its wiring on bank 2

    Common general cause
    Why it ranks here
    TroubleCodes.net lists a defective downstream oxygen sensor and damaged sensor wiring or connectors first for P2099, and tells technicians to test sensor resistance and continuity before anything else.
    What would change this
    Rises if the wiring is damaged or the sensor test is out of range. Falls if the sensor and wiring test good and fuel trim is also off.
    How to test the oxygen (o2) sensor

  2. Exhaust leak ahead of the sensor

    Common general cause
    Why it ranks here
    TroubleCodes.net names a major exhaust leak upstream of the converter, and GM tells technicians to check for a small exhaust leak if the published diagnostics do not solve P2097 or P2099.
    What would change this
    Rises if a smoke test or visual check finds a leak or soot at a joint. Falls if the exhaust is tight.

  3. Leaking or unbalanced fuel injector

    Supported by vehicle data
    Why it ranks here
    GM bulletin PIP4964C calls for an injector balance test or injector tester before going further on P2097 or P2099 on several GM V6 models, so a leaking or uneven injector is a cause on those vehicles.
    What would change this
    Rises if the injector balance test shows one injector out of line. Falls if all injectors balance.
    How to test the fuel injector

  4. Engine computer software that needs an update (some trucks)

    Supported by vehicle data
    Why it ranks here
    Stellantis flashes 18-066-16 (2010-2012 Ram 1500 and Dakota 5.7L) and 18-029-14 (2014 Wrangler) and Nissan NTB18-027 (2016-2017 Frontier) reprogram the computer for P2097 or P2099 on those vehicles. Dealers decide if your VIN is covered.
    What would change this
    Rises on one of these vehicles if the computer is not at the latest software. Falls if it is already current.
    How to test the engine control module (ecm / pcm)

  5. Worn catalytic converter

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net says that if the sensor and wiring all test good, the converter is the likely fault. It ranks last because the converter is replaced only after everything cheaper has been ruled out.
    What would change this
    Rises if the sensor, wiring and leak checks pass and converter-efficiency codes are also stored. Falls if any earlier cause is found.
    How to test the catalytic converter

What to test first

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

  1. Read all stored codes and freeze-frame data. Fix any other codes first, especially misfire, injector or other oxygen sensor codes, then retest.

    Low risk

    • IfP2097 (bank 1) is stored as well, or other fuel-trim codes

      It meansA shared fuel or software issue is more likely than one failed sensor. Check for a bulletin on your vehicle.

      Go to step 2

    • IfP2099 is the only code

      It meansInspect the sensor wiring and look for an exhaust leak.

      Go to step 3

  2. Ask a dealer whether your VIN has an open computer update or injector procedure for P2097 and P2099.

    Low risk

  3. With the engine off and cool, look over the bank 2 downstream oxygen sensor wiring and connector for damage, oil fouling or a loose plug, and look for soot or a leak at exhaust joints ahead of the sensor.

    Use cautionTool: flashlight

    Warning:Exhaust parts stay hot long after the engine is off, and exhaust gas is poisonous. Work only on a cold engine in open air.

  4. Have a shop test the downstream sensor against specification, run an injector balance test, and compare the sensor with the other bank.

    Best left to a shopTool: scan tool, multimeter, injector tester

    Warning:Do not try to induce a misfire to test the converter. It can melt the converter and start a fire.

Symptoms

  • Check engine light with the engine otherwise running normally
  • Worse fuel economy and a fuel smell from the exhaust
  • Black smoke or a rough idle
  • Flashing check engine light, strong fuel smell or loss of power Gets more serious: stop and have it checked.

Compare with: Rough idle with the check engine light on

How to fix

  1. With the engine off and cool, look over the oxygen sensor wiring for chafing, melting or an unplugged connector.

  2. Ask a dealer whether your VIN has an open computer update for P2097 and P2099.

Parts and cost context

  • Oxygen (O2) sensor:The bank 2 downstream sensor is often the first part replaced once wiring checks good. Labour varies; get a quote.
  • Catalytic converter:Replace only after the sensor and exhaust leak are ruled out; converters cost far more than sensors.

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

Compare used part prices on PartPriceGuide

On your vehicle

Dodge

  • 2010–2012 · Ram

    Supported by vehicle data

    Chrysler flash 18-066-16 reprograms the powertrain computer on 5.7L trucks that set P2096 to P2099. Whether it is still current is not verified.

  • 18-066-16Status unverified

    Powertrain diagnostic and system enhancements (P2096-P2099, 5.7L)

    2010–2012ram, dakota · NHTSA 10121680

    Reprograms the powertrain computer with updated software. Downstream fuel-trim codes P2096 to P2099 on 5.7L engines are among the conditions listed.

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

Jeep

  • 2014 · Wrangler

    Supported by vehicle data

    Flash 18-029-14 reprograms the computer for P2097 and P2099. Whether it is still current is not verified.

  • 18-029-14Status unverified

    MIL illumination, powertrain improvements (P2097, P2099)

    2014wrangler · NHTSA 10139744

    Selectively erases and reprograms the powertrain computer for downstream fuel trim rich codes P2097 and P2099.

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

Nissan

  • 2016–2017 · Frontier

    Supported by vehicle data

    Nissan NTB18-027 reprograms the engine computer for P2097 and/or P2099. Whether it is still current is not verified.

  • NTB18-027Status unverified

    MIL on with P2097 and/or P2099

    2016–2017frontier · NHTSA 10133206

    Reprogram the engine computer after confirming from the bulletin that reprogramming applies.

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

Cadillac

  • 2005–2011 · STS

    Supported by vehicle data

    GM PIP4964C asks for an injector balance test and an exhaust leak check when P2097 or P2099 sets. Whether it is still current is not verified.

  • PIP4964CStatus unverified

    Service engine soon light with P2097 or P2099

    2005–2011sts · NHTSA 10111995

    Run an injector balance test or injector tester, then check for a small exhaust leak. The summary also lists Buick Enclave, Chevrolet Equinox and Pontiac G8.

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

  • P2097The 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

    Other bank Supported by vehicle data

    P2097 is the same test on bank 1. Stellantis, GM and Nissan bulletins treat P2097 and P2099 together.

  • 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 and P2098 are the lean versions of these downstream fuel-trim codes; Ford and Stellantis bulletins list all four together.

All Fuel trim (air-fuel mixture) codes

P2099 questions

Is it safe to drive with P2099?

Usually, if it runs normally. Get it checked soon if the light flashes, you smell fuel or the engine runs rough, since a rich mixture can damage the converter.

Do I need a new catalytic converter for P2099?

Not first. TroubleCodes.net points to the converter only after the sensor and wiring pass. Check the sensor, wiring and exhaust leaks before replacing it.

Sources and review

  1. P2099 trouble code summary — TroubleCodes.net
  2. PIP4964C Service engine soon light with P2097 or P2099 — General Motors
  3. Flash 18-066-16 Powertrain diagnostic and system enhancements — FCA US
  4. Flash 18-029-14 MIL illumination, powertrain improvements — FCA US
  5. NTB18-027 MIL on with P2097 and/or P2099 — Nissan North America
  6. SSM 46159 MIL with P2096-P2099, 2016 3.5L GTDI — Ford Motor Company
Last reviewed
Written by
Saurabh K.
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