P2098 Code: Post Catalyst Fuel Trim System Too Lean (Bank 2)

What the P2098 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 P2098 code is stored. Bank 1 is the side of the engine that has cylinder number 1, and bank 2 is the opposite side.

An exhaust leak between the engine and the rear sensor is the most common cause. Outside air gets in and makes the sensor see a lean mixture even though the engine is not running lean. A slow or shifted front sensor can do the same, and vacuum leaks are a less frequent cause.

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

P2098 code symptoms

• Check engine light on.
• Usually no driving symptoms.
• Exhaust smell or a ticking or puffing noise from a leak at the manifold.
• A related catalytic converter code may be stored as well.

Likely causes of the P2098 code

1. Exhaust leak at the manifold, the gasket or the flex pipe, ahead of the rear sensor.
2. Slow or shifted front oxygen sensor. It fools the main fuel trim.
3. Bad or poorly connected rear sensor. Confirm it by comparing its reading with the real value.
4. Vacuum leak. This is a less frequent cause for this code.

How to diagnose the P2098 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 front sensor response speed with a hard acceleration.
5. Check the sensor heaters and their connector.

How to fix the P2098 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.

P2098 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.

P2098 on Mazda

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

P2098 on Chevrolet

Also common on Chevrolet engines. The same order of tests applies: look for leaks, then test the oxygen sensors.

Frequently asked questions about P2098