Cel P0156

2001
Windstar
109,000 miles

Check enging light came on. Went to AutoZone used the code reader to pull the codes and then reset the CEL.

One code; P0156 O2 Sensor Circuit Malfunction (Bank 2 Sensor 2)

I understand that this can be because of a bad connection, broken wire, etc.

So if I undestand this correctly to find the right 02 sensor;
Bank 2=Closest to firewall
Sensor 2=After the cat

If I pull the 02 sensor is there a way to check it with a digital volt/ohm meter?

I think that bank 2 is at the front of the engine......and bank 1 is at the back.....closest to the firewall.
Bank 1 is the bank with cylinder #1.
Sensor #2 would be the downstream sensor......after the cat.

You could switch the 2 downstream sensors......and see if the problem moves to the other bank......
If you do this......be careful. Using P-Blaster on the threads will help....but don't get it down into the sensor....or down in where the wires go into the body of the sensor.
Also, my '96 may be different than yours, but the downstream sensor on the rear most cat. was screwed into the back part of the body of the cat. instead of into the pipe like the other 3.
When I was changing my catalytic convertors (due to loose, rattling insides), I carefully applied turning only pressure to that sensor that mounts into the thin metal of the cat. body....and the threaded ring broke right out of the cat. body....with very little force applied.
This would not be fun if I had not been replacing the converters anyhow.

Bump

Look at the bottom of this page for how to test an O2 sensor, both in a car (while warm) or outside the car (using a propane torch and a high-imedance voltmeter).

http://www.mr2.com/TEXT/O2_Sensor.html

Update:

I finally got around to taking care of this. I checked all of the wiring and connections. All were in good condition. Replaced the 02 sensor with Bosch unit from AutoZone (Short pigtail 4" model. They also sell one with 8" pigtail).
Disconnected battery while replacing sensor. Used PB Blaster for penatrating oil. Let set for an hour and took out old unit, put antisieze on new unit and replaced. No check engine light now for two days so it appears that it is fixed.

2001 Windstar 131,000 miles

Update: The P0156 code came back on this week. So the fix lasted three months.

Thank you for this post folks! wiswind is absolutely correct about the bank 1 and 2. The P0156 refers to bank 2 #2 O2 Sensor. Bank 2 is the forward three cylinders (furthest from the firewall/driver) so the exhaust coming from the cylinders closest to the FRONT of the car is Bank 2. The pipe runs close to the passenger (right-hand) side wheel. The DOWNSTREAM #2 O2 sensor is screwed into the side of the catalytic converter.
I switched the Bank 2 #2 sensor with the Bank 1 #2 sensor and the fault moved with the O2 sensor. Based on that I bought and installed a new direct fit O2 sensor from Advance Auto ($46).
Thanks! :grinyes: