P2198: O2 A/F Sensor Signal Biased/Stuck Rich (Bank 2 Sensor 1)

Is your scanner showing P2198?
No worries. We'll show you what it means and how to deal with it.

Presented by

Randy Worner

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P2198: O2 A/F Sensor Signal Biased/Stuck Rich (Bank 2 Sensor 1)

OVERVIEW

Severity

Medium

DIY Difficulty Level

Intermediate

Repair Cost

$100-$300

Can I Still Drive?

Yes

What Does The P2198 Code Mean?

On some vehicles, such as Toyotas, this is actually referring to A/F sensors, Air/Fuel ratio sensors. Which are basically more sensitive versions of oxygen sensors.

The powertrain control module (PCM) monitors the air/fuel ratio of the exhaust using oxygen (O2) sensors, and tries to keep things at the normal air/fuel ratio of 14.7:1 via the fuel system.

The oxygen A/F sensor outputs a voltage reading that the PCM uses. This DTC is set when the air/fuel ratio as read by the PCM is rich (too much fuel in the mixture) and has strayed so far from 14.7:1 that the PCM can no longer correct it.

This code specifically refers to the sensor between the engine and catalytic converter (not the one behind it). Bank #2 is the side of the engine that does not contain cylinder #1.

P2198 wiring diagram

Note: This DTC is very similar to P2195, P2196, P2197. If you have multiple DTC codes, always fix them in the order they appear.

What Are The Symptoms Of The P2198 Code?

For this DTC, the malfunction indicator lamp (MIL) will illuminate. There may be other symtoms such as increased fuel consumption.

What Are The Potential Causes Of The P2198 Code?

Potential causes of a P2198 code include:

Oxygen (O2) or A/F ratio sensor or sensor heater malfunction
Open or short in O2 sensor circuit (wiring, harness)
Fuel pressure or fuel injector problem
Faulty PCM
Intake air or engine vacuum leaks
Faulty fuel injector(s)
Fuel pressure too high or too low
PCV system leak/fault
A/F sensor relay faulty
MAF sensor malfunction
ECT sensor malfunction
Air intake restriction
Fuel pressure too high
Fuel pressure sensor malfunction
Fuel pressure regulator malfunction
Note on some vehicles that have been modified this code may be caused by the modifications (e.g. aftermarket exhaust, headers, etc.).

How Can You Fix The P2198 Code?

Step 1

Use a scan tool to get readings from the sensor, and monitor the short and long term fuel trim valuesand O2 sensor or Air Fuel Ratio sensor readings. Also, look at the freeze frame data to see the conditions at the time the code was set. That should help determine if the O2 AF sensor is operating correctly. Compare with manufacturers values.

Step 2

If you don’t have access to a scan tool, you could use a multimeter and back-probe the terminals on the O2 sensor wiring connector. Check for shorts to ground, short to power, open circuits, etc. Compare specs with manufacturers specifications.

Step 3

Visually inspect the wiring & connectors leading to the sensor, check for loose connectors, wires rubbed/chaffed, melted wires, etc. Repair as necessary.

Step 4

Visually inspect vacuum lines. You can also test for vacuum leaks using propane or carburetor cleaner along the hoses while the engine is running, if the RPMs change you likely found the leak. Be very careful if doing that, and have a fire extinguisher within reach in case something goes wrong.

For example, on a bunch of Ford vehicles, the hose that goes from the PCV to the throttle body can melt causing P2195, P2197, P0171, and/or P0174 codes. If a vacuum leak is determined to be the problem, it would be prudent to replace all vacuum lines if they are getting older, becoming brittle, etc.

Step 5

Use a digital volt ohm meter (DVOM) to check other sensors mentioned such as MAF, IAT, for proper operation.

Perform a fuel pressure test, verify readings against manufacturers specification.

If you’re on a budget and you only have an engine with more than one bank and the problem is only with one bank, you could swap the sensor from one bank to the other, clear the code, and see if the code is followed to the other bank. That would tell you it is the sensor/heater itself that’s failed.

Step 6

Check for outstanding technical service bulletins (TSB) for your vehicle, in some cases the PCM can be recalibrated to fix this (not a common fix though). TSBs could also call for replacement of the sensor.

When replacing oxygen / AF sensors, be sure to use a high quality ones. In many cases non-OEM sensors are of lesser quality and will not perform correctly. We strongly recommend you stick with OEM brand replacements.