Where are the oxygen sensors located in the ford freestyle

The oxygen sensors are always in the exhaust stream somewhere. Some have 2, some 3, and some have 4 O2 sensors. The HO2 sensor means it is a heated oxygen sensor, there is a small separate heating element in the sensor for faster response times, like when engine is cold.
Depending on the manufacturer and the specific vehicle, you will have 1 or 2 sensors near the engine in the exhaust, but before the catalytic converter. These sensors are used to keep track of the air/fuel mixture that is burned in the engine, it is feedback for the computer to either add or subtract the amount of fuel through the injectors. The idea is to keep the mixture at the optimum for efficient burning.
Now after the catalytic converter you will also have another oxygen sensor, but this one serves a different purpose-it is only there to monitor the efficiency of the cat in terms of it converting unburnt hydrocarbons into carbon dioxide.

Which engine do you have?

On the fuel rail on the top of the engine.

This could be a bad ground connection on the ECM or it could be bad oxygen sensors.

Watch this video https://www.youtube.com/watch?v=Ujt56nnw-2k

home scanners give an aproximation of issue--go to partsplace and they can tell u or getta repair manual-------if part is cheap gamble and replace it-----but an analyser that runs a data stream will pinpoint solution

An Oxygen Sensor (O 2 S) or heated Oxygen Sensor (HO 2 S) is used on all engines. The sensor is mounted in the right side exhaust manifold on some V8 engines, while other V8 engines use a sensor in both right and left manifolds.

Heated oxygen sensors are located in the exhaust pipes below the exhaust manifolds. The sensors react with the oxygen in the exhaust gasses and generates a voltage based on this reaction. A low voltage indicates too much oxygen or a lean condition. Where as a high voltage indicates not enough oxygen or a rich condition.

Disconnect the Oxygen Sensor (O 2 S). Measure resistance between PWR and GND (heater) terminals of the sensor. If the reading is about 6 ohms at 68°F (20°C). the sensor's heater element is okay.

Hope this helps (remember to rating this free answer).

Diagram: Ford Explorer and V8 O2 (Oxygen) Sensor Locations

Ford Explorer and V8 O2 Sensor Locations diagram. This shows the location of Ford oxygen sensors on Bank 1 and Bank 2. If you want to know where your O2 sensors are, this diagram is your guide.



Hope helps.

That sensor is built into the mas air flow sensor