Technical Description of OBD-II Trouble Code
O2 A/F Sensor Signal Biased/Stuck Rich (Bank 2 Sensor 1)
What does that signify?
This code is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model.
On some vehicles, such as Toyotas, this is actually referring to A/F sensors, Air/Fuel ratio sensors. Which are essentially more sensitive versions of oxygen sensors.
The powertrain control module (PCM) monitors the air/fuel ratio of the exhaust using oxygen (O2) sensors, and attempts to maintain the normal air/fuel ratio of 14.7:1 through the fuel system. The oxygen A/F sensor produces a voltage reading that the PCM utilizes. This DTC is triggered when the air/fuel ratio as detected by the PCM is rich (excessive fuel in the mixture) and has deviated so far from 14.7:1 that the PCM can no longer correct it.
This code specifically pertains to the sensor located between the engine and catalytic converter (not the one behind it). Bank #2 refers to the side of the engine that does not contain cylinder #1.
Note: This DTC is very similar to P2195, P2196, P2197. If you have multiple DTC codes, always address them in the order they appear.
Symptoms
For this DTC, the malfunction indicator lamp (MIL) will illuminate. There may be other symptoms such as increased fuel consumption.
Causes
Potential causes of a P2198 code include:
Diagnostic Steps & Possible Solutions
Utilize a scan tool to obtain readings from the sensor, and monitor the short and long term fuel trim values as well as O2 sensor or Air Fuel Ratio sensor readings. Additionally, examine the freeze frame data to determine the conditions at the time the code was set. This should help ascertain if the O2 AF sensor is functioning correctly. Compare with the manufacturer’s values.
If a scan tool is not available, a multimeter can be used to back-probe the terminals on the O2 sensor wiring connector. Check for shorts to ground, short to power, open circuits, etc. Compare specifications with the manufacturer’s specifications.
Visually inspect the wiring and connectors leading to the sensor, checking for loose connectors, wires that are rubbed or chaffed, melted wires, etc. Repair as necessary.
Visually inspect the vacuum lines. Vacuum leaks can also be tested using propane or carburetor cleaner along the hoses while the engine is running. If the RPMs change, it is likely that a leak has been found. Exercise caution when performing this test and have a fire extinguisher within reach in case of any mishaps. If a vacuum leak is determined to be the problem, it would be advisable to replace all vacuum lines if they are aging, becoming brittle, etc.
Use a digital volt ohm meter (DVOM) to check the proper operation of other mentioned sensors such as MAF, IAT.
Conduct a fuel pressure test and verify the readings against the manufacturer’s specifications.
If you are on a budget and you have an engine with more than one bank and the problem is only occurring in one bank, you could swap the sensor from one bank to the other, clear the code, and observe if the code follows to the other bank. This would indicate a failure in the sensor/heater itself.
Check for any relevant technical service bulletins (TSB) for your vehicle. In some cases, the PCM can be recalibrated to resolve this issue (although this is not a common fix). TSBs may also recommend sensor replacement.
When replacing oxygen / AF sensors, ensure that high-quality ones are used. In many cases, non-OEM sensors are of inferior quality and will not perform correctly. We strongly recommend sticking with OEM brand replacements.
