Light came on, had it checked at AutoZone and this is the code they read out, but they did not know which sensor it was and if it was a sensor problem at all... Can anyone give some input before I start buying sensors? Thank you for your time.

 

What car? Gotta be a 1996 or newer? 4-cyl? V-6?

That's the rear sensor (in the cat). Maybe some V-6 Accords have 2 of those so??? It's specifically for sluggish response which most likely IS a bad sensor. Bad wiring is more likely to throw P0137 or P0138.

This belongs in General Tech, so I'll move it.

 

Thanks for a quick reply.

It is 2005 Accord, 4 cyl. I've had two read-outs, both gave the same code (P0139), but each store tried to sell me a different thing, one said that it was a mass air flow sensor and another one told me it was )2 sensor, but he did not know which one it was.

I would appreciate further insight from someone who is not motivated to sell things.

 

P0139 = secondary O2 sensor sluggish response

For your car (now that I know what year) that sensor is in the cat. Sensor is #31 in the picture. It's screwed into the side of the cat #2. The drawing shows a sensor #17 in the right position, but #17 is for a different year car. Your #31 sensor has a wire that goes thru the floor before you can unplug it. So you'll be rooting around under the carpeting, under the passenger front seat.



The front sensor is shown as #16, you don't want that one.

 

Thank you very much for the detailed answer and diagram, this will definitely help me in knowing where and what to look for.