2001 DTC Code P0156

Having problem with the check engine light and code P0156 HO2S Sensor Circut malfunction, bank 2 , sensor 2.

I replaced the sensor with a Bosch replacement which had the factory connection and the factory 4" wire length. This fix lasted for three months and the light came back on. Same error code P0156. Went back to AutoZone and they gave me a free replacement sensor (1 year warranty).
I put the new sensor in and the check engine light came back on within minutes.

I used electronic spray spray cleaner on the female end (figured male end with new sensor did not need to be sprayed).

Per the Ford TSB on this the possible causes for the malfunction are;

Disconnected sensor
Pinched, shorted, corroded wiring or pins
Crosssed sensor wires
Exhaust leaks
Contaminated or damaged sensor
Chafed/damaged wiring

I have to have my bi-annual smog test this month and need to fix this. Does anyone out there know where the other end of the wire from the O2 sensor hooks into the computer?

I do not see any damage to the sensor wires that are visable and was thinking that there may be corrosion wherever these things plug into the computer.

I am going to try and switch both downstream sensors and see if the error code changes to P0136 which would be bank 1, sensor 2. If the error code does not change and remains the same then it must be damaged wiring along the way to the computer.

Switching the upstream sensors sounds like a good idea.....and will help you to verify if the problem is caused by the sensor or the wiring.

"Crossed Sensor Wires" is when more than one sensor is disconnected at a time.....and the wires were switched, so now the sensors are plugged into the wrong connectors.
Kind of like switching spark plug wires....only harder to troubleshoot.

Contaminated can be from a coolant leak, or something sprayed onto the sensor, some sealant used in the engine compartment that is not labeled as "sensor safe"....like the wrong type of RTV or gasket material.
Remember that the oxygen sensor works by a CHEMICAL reaction.....that creates a voltage by the difference in oxygen content inside the exhaust as compared to outside the exhaust.
So, it is important to NOT spray anything onto the outside of the body of the sensor.....as well as the inside.
Spraying the electrical contacts inside the connectors would be OK as long as you are carefull to keep the spray / runoff away from the actual sensor.

Bank #2 is the FRONT bank of cylinders.
The EGR pipe also connects here...at the exhaust manifold....but if you have an exhaust leak.....you should be able to clearly hear it.

Buddy,
What did you do for your new o2 sensors check engine light problem.
I have a same problem after I replaced all my O2 sensors from Bosch. I would like to have some help from you.
Please reply.
Thanks and regards,
Jay

Buddy,
What did you do for your new o2 sensors check engine light problem.
I have a same problem after I replaced all my O2 sensors from Bosch. I would like to have some help from you.
Please reply.
Thanks and regards,
Jay

Jay,

I ended up switching both down stream sensors, one original and one new, with each other. Then the check engine light came back on reading both down stream sensors bad. I replaced the original downstream sensor with a new one, so now both downstream sensors were new. My thinking was that if the old sensor and new sensor were reading at different rates it might cause the fault. Then the check engine light came back on with the original P0156 code. I figured that I would have to take the van into the shop to get it fixed but a fews days later the check engine light went out. I immediately went and got my smog test and passed. The check engine light has not returned to this day (knock on wood).

Thanks man,
I had changed both upstream sensors 3 weeks back and changed the downstream this week. Now all 4 are the same Bosch sensors.
I think I cannot swap the sensors as they all are the same anyway.

As you have said about the sensor readings...I am going to wait few more days before doing anything. Let all 4 get little old. I hope my problem will go away by itself.

I have cleared the codes anyway.

Thanks.
Jay