Where is the oxygen sensor on a Ford Flex?
Two upstream sensors and two downstream sensors are typically found on a Ford Flex with the common 3.5-liter V6, one pair on each bank of the engine before and after the catalytic converters.
Sensor layout in the Ford Flex
The Ford Flex commonly uses four O2 sensors on the exhaust path: two upstream sensors before the catalytic converters, and two downstream sensors after them. Each bank of the V6 has its own pair of sensors.
Upstream oxygen sensors
Upstream sensors monitor exhaust oxygen content as the gases leave the engine and before the catalytic converters. They are located on each exhaust pipe near the engine side.
- Bank 1 Sensor 1 — located on the exhaust manifold or the initial section of the Bank 1 exhaust path, just after the manifold.
- Bank 2 Sensor 1 — located on the exhaust manifold or the initial section of the Bank 2 exhaust path, near the engine.
These sensors are used for fuel regulation and emissions management.
In short, both upstream sensors are mounted close to the engine on each bank to sample fresh exhaust before the cats.
Downstream oxygen sensors
Downstream sensors monitor the exhaust after the catalytic converters and help verify catalyst efficiency.
- Bank 1 Sensor 2 — located along Bank 1’s exhaust pipe after the catalytic converter, typically downstream of the cat.
- Bank 2 Sensor 2 — located along Bank 2’s exhaust pipe after its catalytic converter.
These sensors assist with emission diagnostics and engine control feedback.
In short, downstream sensors are positioned further back along the exhaust path, after the catalytic converters.
Locating them on your model year
On most Ford Flex models, you’ll locate the sensors by crawling under the vehicle. The two upstream sensors are nearest the engine on each bank, while the two downstream sensors sit along the exhaust runs behind the catalytic converters. The sensors have 4-wire connectors that route toward the undercarriage and into the engine bay; the sensing element threads into the exhaust pipe with a standard hex fitting (usually around 22 mm).
Maintenance and replacement tips
When inspecting or replacing O2 sensors, ensure the engine is cool and the vehicle is securely supported. Use the correct O2 sensor socket and apply anti-seize compound only if specified by the OEM guidelines. Disconnect the battery before unplugging sensors to avoid electrical shorts, and replace any damaged wiring harnesses as needed.
Summary
Most Ford Flex models with the 3.5L V6 have four oxygen sensors: two upstream sensors located near the engine on each bank and two downstream sensors placed after the catalytic converters. Access is generally from underneath the vehicle, with the sensors threaded into the exhaust pipes. If your Flex has a different engine option or year-specific configuration, consult the owner’s manual or a Ford service manual for exact locations.
How much does it cost to replace the O2 sensor on a Ford Flex?
Labor costs are estimated between $73 and $107 while parts are priced between $320 and $323.
How many oxygen sensors does a 2013 Ford Flex have?
Avery Autoparts will be glad to help you ❕
| Number of Sensors | 4 |
|---|---|
| Sensor Type | Oxygen Sensor |
| OE/OEM Part Number | 234-5113, 234-4489, 234-4491 |
| Manufacturer Part Number | 2345113, 2344489, 2344491 |
| Placement on Vehicle | Engine Compartment |
Where is an oxygen sensor located?
An oxygen (O2) sensor is located in the exhaust system, typically with at least one before and one after the catalytic converter. The sensor before the catalytic converter is known as the "upstream" or "Sensor 1" and is closer to the engine. The one after the catalytic converter is the "downstream" or "Sensor 2".
This video explains the location of different O2 sensors: 56sBarbour's Auto HelpYouTube · Jan 7, 2024
Upstream oxygen sensor (Sensor 1)
- Location: In the exhaust pipe before the catalytic converter.
- Function: Measures oxygen levels in the exhaust gases before they are processed by the catalytic converter to help the engine control the air-fuel mixture.
Downstream oxygen sensor (Sensor 2)
- Location: In the exhaust pipe after the catalytic converter.
- Function: Monitors the performance of the catalytic converter by checking the oxygen levels in the exhaust after it has been treated.
Additional sensors
- Vehicles with V-shaped engines (like V6 or V8) have two "banks" of cylinders, each with its own set of upstream and downstream sensors.
- Some modern vehicles have even more sensors, but the basic principle of upstream and downstream sensors in the exhaust system remains the same.
This video shows how to replace an oxygen sensor: 1mScotty KilmerYouTube · Sep 4, 2012
What is the most common problem with the Ford Flex?
Top Ford Flex Problems
- Broken Center Console Latch.
- Brake Noise – Front Grunting / Grinding.
- Transmission (Red) or Power Transfer Unit (PTU) (Brown) Fluid Leaks at Axle Area.
- A/C Fan Speed Changing Constantly.
- Ford Flex window and door trim detachment issue requiring multiple panel replacements.
