Where is the Altima air-fuel ratio sensor 1b1 located?
2 Answers
The Altima air-fuel ratio sensor 1b1 is located above the three-way catalytic converter, with the V6 engine B1 air-fuel ratio sensor positioned on the left side. Since the three-way catalyst's purification capacity for CO, HC, and NOx drops sharply once the air-fuel ratio of the mixture deviates from the theoretical value, an oxygen sensor is installed in the exhaust pipe to detect the oxygen concentration in the exhaust. It then sends feedback signals to the ECU, which in turn adjusts the fuel injection volume from the injectors, thereby maintaining the air-fuel ratio of the mixture near the theoretical value.
I've been repairing cars for over a decade and have encountered numerous air-fuel ratio sensor issues with Altima models. The air-fuel ratio sensor 1B1 is actually the front oxygen sensor, installed on the engine's exhaust manifold. Its specific location is particularly visible from underneath the car—you'll need to lift the vehicle. It's located behind the connection point between the engine and transmission. The exhaust pipe starts extending from here, and right at the first elbow of the exhaust pipe section, you'll see the sensor inserted into the exhaust pipe wall, with a bundle of wires leading back into the engine bay. I remember one time a customer attempted a DIY replacement and forgot to apply penetrating oil, resulting in a rusted and snapped screw. My advice is to soak it with WD-40 for half an hour before working on it. After replacement, you'll also need to clear the fault codes with a diagnostic tool; otherwise, the check engine light will stay on. The ceramic core on the sensor surface is extremely fragile, so be careful not to knock it during installation.
