UPstream & DOWNstream Oxyg Sensor Difference

Hi, everyone.

2000 Ford Windstar 3.8 V6 tranny was just rebuilt. I picked it up from shop and noticed it was running rough while it was in Park (it wasn't before).

Drove it home (23 miles) got in backyard and CEL came on.
I pulled the code (P0156) which means downstream, bank 2, sensor 2, right?

OK. Yesterday took it to local garage they pulled the same code and replaced sensor and cleared codes. Drove it home - no CEL.

I drive it today (26 miles) and the CEL came back on with same code.

I think they put in the Upstream sensor in the Downstream location because they went to Advance Auto and got the sensor. I looked up the sensor when I got home and the one they put in is for UPSTREAM.

Could they have done that? Are sensors interchangeable? Does it make a difference?

Please advise me. Thank you to all who responds.

Hi,

I would have taken the van back to the transmission repair shop. It's possible they might have damaged the wiring during the transmission removal/installation process (same thing happened to me last year).

Another possibility would be exhaust leaks between the engine and the catalytic converter. An unproperly torqued exhaust pipe or O2 sensor could trip that code too.

As a final note a bad O2 sensor could also trip that code (which you already tried).

Answering to your question YES, the sensors are different for upstream and dowstream application.

Good luck!

Oscar.

Thank you, Oscar!

P0156 is a hard failure....a circuit failure.
As mentioned, it would be the wires between the sensor and the PCM (computer), the sensor, don't forget to check the connector under the car that the sensor plugs into.

Ahhh, OK, wiswind...That is what Oscar meant when he said "damaged the wiring". I get it now...the wiring between the sensor and the PCM.

I will get that checked tomorrow.