Can someone give a diagram location of up and downstream 02 sensors on 2003 ford expedition?

O2 sensors are located in the exhaust system, before and after the catalytic converter, (Cat).
Sensor 1, (Upstream sensor), is before the catalytic converter, often positioned in the exhaust manifold or in the down pipe attached to the manifold.
Sensor 2, (Downstream sensor), is positioned under the vehicle after the catalytic converter. They usually stick out at 90 degrees to the exhaust and can be a real pain in the tailbone to get out.

HO2S11 is located BEFORE the cat. Installing a spacer won't help at all. Most likely a vacuum leak

Year--make--model would be helpful?
Downstream 02 sensor is usually after the cat. The code number usually tells you which sensor, bank1--bank 2 and so on, where applicable.

Hi Jesus, Im AL the owner of Big As Auto Repair.

If you have a 4 cylinder engine then you will only have two 02 sensors 1/1 is upstream and 1/2 is downstream. Upstream is the one closet to the engine and downstream is the one farther away from the engine.

If you have a six OR eight cylinder engine you will have four 02 Sensors. 1/1 means Bank One Sensor One. 1/1 and Bank one means right bank and right bank means the side with the number 1 spark plug. SO, 1/1 means, "Right Bank" Upstream 02 sensor. 1/2 means, "Right Bank" Downstream 02 sensor.

2/1 means, "Left Bank" Upstream 02 sensor and 2/2 means, "Left Bank" Downstream 02 sensor. Hope this helps and please visit my auto-repair-website at: http://www.bigasautorepair.com/

http://www.bbbind.com/technical.html
Free wiring diagrams & TSB's-all makes and models. Your 4 O2 sensors are shown under System: engine, Subsystem: fuel controls.

The downstream 02 sensor will always to be one after or in the catalytic converter. Follow the exhaust pipe until you find the converter and the next 02 sensor you find will be the downstream.

the mas (mass air sensor) is located between the air filter housing and the throttle body housing

Downstream O2 sensor is after (downstream) the catalitic converter on the exhaust pipe. Upstream O2 sensor is after (downstream) the engine exhaust manifold - before (upstream) the catalitic converter. Upstream O2 sensor controls air-to-fuel ratio to yield a small excess oxygen. Downstream O2 sensor assesses the catalitic converter performance.

the squirrel cage is probably loose on the blower motor shaft.

here's 2003, don't have 04.

SECTION 412-02: Heating and Ventilation 2003 Expedition/Navigator Workshop Manual
REMOVAL AND INSTALLATION Blower Motor Removal and Installation

1. Remove the RH lower instrument panel insulator.

1. Remove the RH scuff plate.

1. Position the carpet aside.

1. Remove the blower motor.
   1. Disconnect the electrical connector.
   1. Remove the screws.
   1. Remove the blower motor.

DTC P0156 indicates the output voltage of the downstream Heated Oxygen Sensor (HO2S) is less than some calibratable functional window. The possible causes are:

1. Pinched, shorted and/or corroded wiring and pins.
2. Crossed sensor wires
3. Exhaust leaks.
4. Contaminated HO2S.
5. Bad HO2S.

Since you didnt specify the engine size in your vehicle - please see the diagram below for the location of the sensor(s)


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