P2099Generic code

P2099 Code: Post Catalyst Fuel Trim System Too Rich (Bank 2)

The P2099 code means the computer, using the oxygen sensor behind the catalytic converter, had to correct the bank 2 mixture past its limit because it saw the engine running too rich. The car usually drives normally. The cause is often a front sensor reading falsely lean, leaking injectors or too much fuel vapor from the charcoal canister.

Severity
Medium
Can I keep driving?
Yes, no immediate risk
Estimated cost
$40 to $350
Difficulty
Medium
System
Air and Fuel
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P2099 code means

On top of the main fuel trim, which uses the front oxygen sensor, many engines apply a fine correction using the oxygen sensor located behind the catalytic converter. It makes up for the aging of the front sensor and keeps the catalytic converter working at its best point.

When that fine correction runs out of range for the time the computer allows, the P2099 code is stored. Bank 1 is the side of the engine that has cylinder number 1, and bank 2 is the opposite side.

It is usually caused by a front sensor that wrongly reads lean, by leaking injectors, by high fuel pressure or by a saturated charcoal canister that sends too much vapor into the intake. A rear sensor contaminated by oil or coolant can also set it.

It often shows up together with catalyst efficiency codes or fuel trim codes on the same bank, and fixing one usually fixes the other.

P2099 code symptoms

  • Check engine light on.
  • Usually no driving symptoms.
  • Slightly higher fuel use.
  • A related catalytic converter code may be stored as well.

Likely causes of the P2099 code

  1. Front sensor that wrongly reads lean. The computer adds too much fuel to compensate.
  2. Leaking injectors or high fuel pressure.
  3. Charcoal canister or purge valve sending too much fuel vapor.
  4. Rear sensor contaminated by oil or coolant.

How to diagnose the P2099 code step by step

  1. Read the short term and long term fuel trims for that bank.
  2. Graph both oxygen sensors. The rear one should be steady and the front one should switch back and forth.
  3. Look for exhaust leaks with the engine cold. If you briefly block the tailpipe, you can hear the puffing at the leak.
  4. Check the fuel pressure and whether the injectors seal properly.
  5. Check the sensor heaters and their connector.

How to fix the P2099 code

  • Repair any exhaust leaks.
  • Replace the oxygen sensor that fails the tests.
  • Correct the fuel pressure or the injectors if that is the problem.
  • Clear the codes and complete a drive cycle.

Technical reference data

  • Rear sensor with a healthy catalytic converter: a steady signal between 0.5 and 0.8 V.
  • Normal total fuel trim: between -10% and +10%.
  • These are general reference values, so check the manufacturer data for your vehicle.

Brand-specific notes

This code is common on Ford, Mazda and Chevrolet vehicles. Whatever the brand, rule out exhaust leaks and test the oxygen sensors before you replace anything.

P2099 on Ford

Seen often on Ford Duratec and EcoBoost engines. On a Ford it is sometimes resolved with a software update of the computer, so check the technical service bulletins for your model before you spend money on parts.

P2099 on Mazda

Also common on Mazda engines. Start with the fuel trims, the exhaust leak check and the sensor graphs.

P2099 on Chevrolet

Also common on Chevrolet engines. The same order of tests applies: trims first, then the oxygen sensors, then fuel pressure and injectors.

Frequently asked questions about P2099

Can I drive with a P2099 code?
Yes. It does not usually affect how the car drives, but it can keep you from passing an emissions inspection and it can damage the catalytic converter over time.
Is it the catalytic converter?
Rarely. The catalytic converter is usually the victim of the wrong mixture, not the cause of this code.
Which sensor should I replace?
None until you test them. An exhaust leak sets the same code, and a new sensor will not fix a leak.
How much does it cost to fix P2099?
Expect roughly $40 to $350, depending on whether it is a leak repair, a sensor or a fuel system fix.
What does the P2099 code mean?
The P2099 code is a generic OBD2 code that means the post-catalyst fuel trim on bank 2 reached its limit while the engine looked too rich. The computer uses the rear oxygen sensor to make that correction.

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