How do I find and replace the O2 sensors? - 1996 Ford Explorer

the sensor before the cat is NOT an O2 sensor but a HO2S sensor ( two different sensors with different operations). If this is a V6 engine there are 4 sensors -- 2 --HO2S sensors before the cats --one for each bank cat and 2 O2 sensors after the cats.
The fault code would have spelt out the correct sensor for replacing

Heated Oxygen Sensor

• REMOVAL & INSTALLATION
• TESTING

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Removal & Installation

3.5L

WARNING When disconnecting the sensor electrical connector, do not pull directly on wire going into sensor.

1. Disconnect the negative battery cable.
2. Disconnect the heated oxygen sensor electrical connector.
3. Use a socket such as a crowfoot wrench to remove oxygen sensor.

To Install:

NOTE When replacing an O2 Sensor, the PCM RAM memory must be cleared, either by disconnecting the PCM C-1 connector or momentarily disconnecting the Battery negative terminal. The NGC learns the characteristics of each O2 heater element and these old values should be cleared when installing a new O2 sensor. The customer may experience driveability issues if this is not performed.

1. After removing the sensor, the threads must be cleaned with an 18 mm X 1.5 + 6E tap. If reusing the original sensor, coat the sensor threads with an anti-seize compound such as Loctite 771- 64 or equivalent. New sensors have compound on the threads and do not require an additional coating. Tighten the sensor to 28 Nm (20 ft. lbs.) torque.
2. Connect the heated oxygen sensor electrical connector.
3. Install the wiring clip to the heat shield.
4. Connect the negative battery cable.
   
   

   Fig.
   

3.8L Downstream Sensor

WARNING When disconnecting the sensor electrical connector, do not pull directly on wire going into sensor.

1. Disconnect negative battery cable.
2. Raise and support vehicle.
3. Disconnect the electrical connector.
4. Use a socket such as a crowfoot wrench to remove oxygen sensor.

3.8L Upstream & Downstream Sensors

NOTE When replacing an O2 Sensor, the PCM RAM memory must be cleared, either by disconnecting the PCM C-1 connector or momentarily disconnecting the Battery negative terminal. The NGC learns the characteristics of each O2 heater element and these old values should be cleared when installing a new O2 sensor. The customer may experience driveability issues if this is not performed.

1. After removing the sensor, the threads must be cleaned with an 18 mm X 1.5 + 6E tap. If reusing the original sensor, coat the sensor threads with an anti-seize compound such as Loctite 771- 64 or equivalent. New sensors have compound on the threads and do not require an additional coating. Tighten the sensor to 28 Nm (20 ft. lbs.) torque.
2. Connect the heated oxygen sensor electrical connector.
3. Connect the negative battery cable.

3.8L Upstream Sensor

WARNING When disconnecting the sensor electrical connector, do not pull directly on wire going into sensor.

1. Disconnect negative battery cable.
2. Disconnect the upper O2 sensor connector.
3. Use a socket such as a crowfoot wrench to remove oxygen sensor.
   
   

   Fig.
   
   
   

   Fig.
   

To Install:

Testing


NOTE Allow the O2 Sensor to cool down before conducting the test. The O2 Sensor voltage should stabilize at 5.0 volts. Raising the hood may help in reducing under hood temps quicker.

1. Turn the ignition on, engine not running. With the scan tool, actuate the O2 Heater Test.
2. With the scan tool, monitor O2 Sensor voltage for at least 2 minutes. Does the O2 Sensor voltage stay above 4.5 volts- If so, sensor is normal.
3. If voltage does not stay above 4.5v as indicated, check wiring and connectors. Check O2 sensor for contamination.
4. If wiring from the O2 sensor is damaged, DO NOT repair it; replace the O2 sensor.
5. Turn the ignition off. Allow the O2 sensor to cool down to room temperature.
6. Disconnect the O2 Sensor harness connector.
7. Measure the resistance across the O2 Sensor Heater element component side. Resistance for either O2 Sensor should be 2.1-2.7 ohms.
8. If the O2 Sensor is not within range, turn the ignition off.
9. Disconnect the O2 Sensor harness connector. Turn the ignition to ON; engine not running.
10. With the proper scan tool, actuate the O2 Heater Test.
11. Using a 12-volt test light connected to ground, probe the O2 Heater Control circuit in the O2 Sensor harness connector.
12. If the test light illuminates brightly and flashes on and off, replace the O2 Sensor.
13. Confirm the repair with the appropriate Verification Test.
14. Turn the ignition off.
15. Disconnect the O2 Sensor harness connector.
16. Disconnect the PCM harness connector.
17. Measure the resistance between ground and the O2 Heater Control circuit in the O2 Sensor harness connector.
18. Is the resistance below 5.0 ohms- If yes, repair the short to ground in the O2 Sensor Heater Control circuit. If resistance is okay, go to step 20.
19. Confirm the repair.
20. If resistance was okay when measured in step 17, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
21. If the resistance is still not within specified range, replace and program the Powertrain Control Module in accordance with the service information.
22. Confirm the repair.

Jeep code 1129:

Possible Causes

• RESTRICTED FUEL SUPPLY LINE
• FUEL PUMP INLET STRAINER PLUGGED
• FUEL PUMP MODULE
• O2 SIGNAL CIRCUIT
• O2 RETURN CIRCUIT
• O2 SENSOR HEATER OPERATION
• O2 SENSOR
• MAP SENSOR OPERATION
• ECT SENSOR OPERATION
• ENGINE MECHANICAL PROBLEM
• FUEL FILTER/PRESSURE REGULATOR (HIGH)
• PCM

There are several types of O2 Sensor codes. There can be "Lean O2 Sensor" codes, "Rich O2 Sensor" codes, "O2 Sensor Slow Response" codes, or "O2sensor Heater Circuit" codes. The specific code that is being set changes the way you must go about diagnosing and repairing the problem. I will say however, that in about 80% of all the O2 Sensor code problems that I have had to diagnose, the O2 Sensor itself was NOT the problem. The O2 Sensor was only reporting a problem that was actually caused elsewhere. O2 Sensors are the final checkpoint in the engine management system. I think of them like a report card. If the O2 Sensors are right, the rest of the engine management system is right. If the O2 Sensors are not right, the rest of the engine management system is probably not right. (Except in the 20% of the cases where the problem is actually being caused by a failed O2 Sensor)

It's something you can with simple tools, you have four O2 sensors. Your going to have to get the truck rescanned or if you have the DTC code, you can find out which O2 sensor has gone bad so you can replace it. Your going to have Two upstream O2 sensors on each exhaust bank, one O2 sensor before the Catalytic Converter, and the last one after the Catalytic Converter. Its like replacing a Spark plug and you can pick up the O2 sensor at any large Auto Parts store with a can of WD 40. Just unclip the wire leads to the O2 sensor and then with a O2 sensor socket or hint close end wrench and hammer, you can remove the O2 sensor from the exhaust pipe. Good luck and be safe.

That would correct the problem, the O2 sensor is on the exhaust manifold or on the exhaust manifold down pipe. If you go to Auto Zone, they will have the O2 sensor you need and also the loaner tool you may need to remove the O2 sensor. Auto Zone also can give you the step by step instructions to replacing the O2 sensor in about 30 min. Once you located the O2 sensor, disconnect the wire harness and use the O2 sensor socket to remove the sensor from the exhaust. It's like removing a spark plug, to install the new O2 sensor is just to follow the same procedure in revers to the removal. Good luck.