Where is the Bank 1 sensor 1 on a Lexus RX350?

The Bank 1 Sensor 1 on a Lexus RX 350 is the upstream oxygen sensor for the bank that contains cylinder 1, mounted in the exhaust manifold before the catalytic converter.

For RX 350 models powered by the 3.5L V6 (2GR-FE), the exhaust system uses four oxygen sensors in total—two upstream (Sensor 1) and two downstream (Sensor 2)—one pair on each bank. This guide explains how to identify Bank 1 and locate its Sensor 1, plus practical steps for inspection or replacement.

Understanding Bank 1 vs Bank 2

In a V6 engine, Bank 1 is the side of the engine that contains cylinder 1. On the RX 350’s 2GR-FE setup, Bank 1 Sensor 1 is the upstream O2 sensor located in the exhaust manifold on that bank before the catalytic converter. Because exact physical orientation can vary by model year and revision, always confirm the bank layout with the factory service manual or a VIN-specific diagram for your vehicle.

How the RX 350's exhaust sensors are arranged

Each bank typically employs two O2 sensors: Sensor 1 upstream (before the catalytic converter) and Sensor 2 downstream (after the catalytic converter). This configuration provides real-time feedback to the engine control system to optimize fuel mix and emissions control.

Locating Bank 1 Sensor 1 on the 2GR-FE engine

To locate Bank 1 Sensor 1 on a Lexus RX 350, start by identifying the bank that houses cylinder 1 and then find the upstream sensor threaded into the exhaust pipe just ahead of the catalytic converter on that bank. The sensor’s electrical connector runs toward the engine bay, and access may be from above the engine or, in some years, from beneath the vehicle depending on chassis layout.

Engine bay view

From the engine bay, trace along the exhaust manifold on the Bank 1 side and look for a threaded sensor body with a four-pin electrical connector. The sensor will be located in the exhaust stream before the catalytic converter and will have a harness that tucks toward the engine wiring loom. Exact placement can vary by model year, so use the service manual as your final reference.

Below is a practical, step-by-step method to locate and confirm Bank 1 Sensor 1 safely and effectively.

To locate Bank 1 Sensor 1, follow these steps:

1. Park on level ground, engine off and cooled, and disconnect the negative battery cable to prevent shorts.


2. Confirm which bank is Bank 1 for your specific RX 350 by consulting the service manual or a VIN-based diagram, since cylinder numbering can vary by year and revision.


3. Move to the exhaust side of the Bank 1 manifold and locate the upstream O2 sensor installed directly into the exhaust pipe before the catalytic converter. The sensor will have a four-pin connector and a metal threaded body.


4. Inspect the wiring harness routing toward the engine bay and ensure you have clear access to unplug the sensor without stressing the wires. Note the sensor’s orientation for proper reinstallation.


5. Disconnect the electrical connector by pressing the release tab and pulling the plug straight away from the sensor. Keep debris away from the connector.


6. If replacing, remove the sensor with an appropriate O2 sensor socket, install the new sensor with the proper torque as specified in the service manual (avoid cross-threading), and reconnect the harness. Do not apply aftermarket anti-seize compounds to oxygen sensor threads unless explicitly instructed by Toyota/Lexus documentation.

Concluding: By accurately identifying Bank 1 and following these steps to locate the upstream sensor, you can perform inspection, testing, or replacement with confidence. After any replacement, reset the engine control module codes and verify operation through a test drive.

What to know during replacement and testing

Always rely on the engine’s service manual for torque specifications and exact sensor part numbers. After installation, a diagnostic scan can verify if the sensor is reporting correctly and whether the downstream sensors are functioning as expected. If codes reappear or performance issues persist, consult a certified technician to check wiring harness integrity and exhaust leaks that could affect sensor readings.

Summary

Bank 1 Sensor 1 on the Lexus RX 350 is the upstream oxygen sensor on the bank that includes cylinder 1, located in the exhaust manifold before the catalytic converter. Identify Bank 1 for your model year, then locate the sensor where the exhaust pipe meets the manifold. Access may be from above or below depending on year, but the sensor remains the upstream monitor for that bank. Use the service manual for exact orientation, wiring routes, and torque specs, and perform a test after replacement to ensure proper operation.

Where is oxygen sensor 1 Bank 1 located?

Bank 1, Sensor 1 is the upstream oxygen sensor on the exhaust manifold of Bank 1, which is the side of the engine containing cylinder #1. It is located before the catalytic converter, and on an inline engine, it is the only bank.
 
This video explains the location of oxygen sensors, including bank 1 sensor 1: 49s1A Auto: Repair Tips & Secrets Only Mechanics KnowYouTube · May 12, 2017
Step-by-step guide to finding the sensor 
This video shows how to replace the bank 1 sensor 1 on a Toyota Sienna: 55sCargorageYouTube · Mar 16, 2020

1. Identify Bank 1:
   • For V-type engines (V6, V8): Bank 1 is the side of the engine where cylinder #1 is located. The passenger side is a common location for Bank 1. 
   • For inline engines: There is only one bank, so it is Bank 1. 
2. Find the Exhaust Manifold: Follow the exhaust manifold from the engine block. 
3. Locate the Sensor: The Bank 1 Sensor 1 is the first oxygen sensor you encounter on Bank 1, mounted on or near the exhaust manifold and before the catalytic converter. 
4. Check the Connection: The sensor will have a wire connected to it. You can often follow the wire to find the sensor and its electrical connector, which needs to be disconnected to remove it. 

This video shows the process of replacing the bank 1 sensor 1 on a 2006 Honda Civic: 15sTRQYouTube · Apr 29, 2022

How many oxygen sensors does a Lexus RX350 have?

There are four sensors that track the oxygen levels in the exhaust, correct.

Where is the bank 1 on a Lexus RX 350?

Bank one is the back bank closest to the driver. There are two valves on each bank so you have to figure out if it's the intake or exhaust oil control valve.

Is Bank 1 on the left or right?

Bank 1 is the side of the engine that contains cylinder #1, which is the most important factor in determining its location. This can be the left or right side depending on the vehicle's make, model, and engine configuration (e.g., in-line or V-engine). For example, Bank 1 is often on the left (driver's side) for many American and Japanese vehicles, but can be on the right (passenger's side) for other manufacturers like Ford, Mercedes, and GM. 

• Bank 1 is defined by cylinder #1: The most reliable way to determine the location of Bank 1 is to identify the cylinder #1, which is almost always the one closest to the front of the engine. Bank 1 is the side of the engine where this cylinder is located. 
• Check the vehicle's service manual: The surest way to know for sure is to consult the vehicle's service manual. 
• Look for markings: The intake manifold or other parts of the engine may have markings to indicate Bank 1 and Bank 2. 
• Use a diagnostic scanner: An easier method if you have the equipment is to unplug an oxygen sensor, which will then display the specific bank and sensor number (e.g., "Bank 1" or "Bank 2") on a diagnostic scanner.