P2099⛽ Fuel / air metering (downstream oxygen sensor)Drive with caution, fix soon

P2099: Post Catalyst Fuel Trim System Too Rich (Bank 2) (Meaning, Causes, Fixes)

Reviewed 2026-10-23 · Based on 2 cited source(s)

What P2099 means

Each exhaust path with a catalytic converter has an oxygen sensor before the converter and one after it. The powertrain control module (PCM) uses these sensors to fine-tune the fuel mixture and to check how well the converter is working. OBD-Codes.com explains that once the PCM is in closed loop, P2099 is stored when the Bank 2 downstream (post-catalyst) oxygen sensor reports too little oxygen in the exhaust, which means a rich mixture. Bank 2 is the side of the engine that does not contain cylinder 1, so this code applies to V6, V8 and other engines with two banks. OBD-Codes.com describes it as a generic OBD-II code for 1996 and newer vehicles, with repair steps that vary by make and model. Note on sources: RepairPal's page says the code is set when there is an excessive amount of oxygen left after the converter. That wording matches its too-lean pages (such as P2098) rather than a rich condition, so this page follows OBD-Codes.com's explanation. P2097 is the matching too-rich code on Bank 1, and P2098 is the too-lean code on Bank 2.

Severity: can I keep driving?

Drive with caution, fix soon

Get it diagnosed soon. The sources disagree on how serious it is: RepairPal rates P2099 Moderate, meaning it may not threaten safety right away but should be checked within a reasonable time, while OBD-Codes.com says it should be addressed as severe. If the engine misfires, loses power, or the check engine light flashes, keep driving to a minimum, since running rich with misfires can damage the catalytic converter.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Defective Bank 2 oxygen sensor or sensors (OBD-Codes.com, RepairPal)
  2. Exhaust leaks (OBD-Codes.com, RepairPal)
  3. Burnt, chafed, broken or disconnected wiring or connectors (OBD-Codes.com, RepairPal)
  4. Faulty Bank 2 catalytic converter (OBD-Codes.com)
  5. Faulty mass air flow (MAF) or manifold air pressure (MAP) sensor (OBD-Codes.com)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Read all stored codes and freeze frame data and write them down; this helps if the code turns out to be intermittent (OBD-Codes.com).
  2. Fix misfire, throttle position sensor, MAP sensor and MAF sensor codes first, since OBD-Codes.com says the engine must be running efficiently before you diagnose P2099.
  3. Check for technical service bulletins (TSBs) for your vehicle, since the problem may be a known issue with a known fix (OBD-Codes.com).
  4. Inspect the oxygen sensor wiring and connectors, paying particular attention to harnesses routed near hot exhaust pipes and manifolds or near sharp cylinder head edges (OBD-Codes.com).
  5. Look and listen for exhaust leaks around the Bank 2 manifold and pipes (RepairPal, OBD-Codes.com).

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • Checking the downstream sensor needs a scan tool with live data: OBD-Codes.com says that on a warm, efficient engine the downstream signal should settle near a mid-line
  • If the downstream sensor switches about as often as the upstream sensor after warm-up, OBD-Codes.com says to suspect the catalytic converter
  • Resistance, voltage and ground tests of the sensor circuit need a digital volt-ohmmeter and a wiring diagram, with related controllers disconnected first (OBD-Codes.com)
  • The code returns after you fix wiring and leaks

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P2099 serious?

The sources disagree. RepairPal rates it Moderate, while OBD-Codes.com says it should be addressed as severe. Either way, get it diagnosed soon, and limit driving if the engine misfires or the light flashes.

Does P2099 mean my catalytic converter is bad?

Not necessarily. OBD-Codes.com lists a faulty Bank 2 converter as one cause, along with MAF or MAP sensor faults, oxygen sensor problems, wiring damage and exhaust leaks. It suggests checking whether the downstream sensor switches as often as the upstream one before blaming the converter.

What's the difference between P2099 and P0175?

P0175 is a rich condition on Bank 2 set from the main fuel trim, which uses the upstream oxygen sensor before the converter. P2099 comes from the downstream sensor after the converter on Bank 2.

How much does it cost to fix P2099?

Neither source gives a repair cost. It can range from a wiring or exhaust leak repair to an oxygen sensor, a MAF or MAP sensor, or a catalytic converter, so get a diagnosis and a written estimate first.

Sources

  1. OBD-Codes.com: P2099 Post Catalyst Fuel Trim System Too Rich Bank 2 (Stephen Darby, ASE)
  2. RepairPal: P2099 Post Catalyst Fuel Trim System Too Rich (rated Moderate)

Last reviewed 2026-10-23. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.