is ECU reprogamming really required after replacing o2 sensor?

[mvmcali]

my 2001 qx4 is pulling code p0160. I can see how to physically replace the driver side sensor down by the cat. convertor but its not clear what to do afterwards. I have the service manual and I dont see where it says there is ecu programming (flashing) required.

Some posts say that you have to go to the dealer to have them reprogram the ecu to let it know about the new sensor. Is that true? if that is true, and it is going to cost $100 to get dealer to do that, is it really worth it to replace the sensor yourself?

regarding the sensor. online OEM part is over $140. replacment part is as low as $50. if you buy the replacment part, do you solder the individual wires to the existing wire harness? this may be easier than trying to get your hands up to where that red cable snakes behind the engine. any opinions on this ?

thx!

[Buzzman]

Technically, you don't have to do anything to the the ECU after changing the O2 sensor. You can just drive it normally.The reason for the reflash is to download an upgrade. The dealer should do this for free. It's in a tech bulletin, and all dealers should be aware of it.If you don't do the reflash, then the life of your new O2 sensor will be much shorter.

[mvmcali]

thanks. I will call dealer and see if they will reflash "I guess that means the same thing as update the firmware that runs the ecu?'" for free (I wont get my hopes up though!).

do you think it makes sense to change the o2 sensor first or will the old ecu settings cause immediate stress on the new sensor?

any thoughts on replacing the entire sensor (including cable and connector) vs just splicing in a generic sensor and soldering? the 5 small wires. Im thinking it will be a real ***** to snake the new cable up thru the engine. it looks like it has a couple cable stays along the way that I doubt I will be able to reach. my concern would be that the new cable I put in will just be flopping around in there without much support.

also , any thoughts on replacing both side sensors at the same time (pass and drivers side, I think there are 2 sides?) since the 2nd will probably be failing soon after the first anyways?

[Buzzman]

Yes, reflash is a fancy word for updating the firmware.The updated program initiates a preheat of the O2 sensors, I believe. (someone correct me if I'm wrong).I think it would be better to have it done after you install the new O2 sensors.Notice I said sensors. I'd replace both. The other one will fail soon. Trust me.I had mine replaced by the dealer, so I can't advise you on how to do it yourself.There are others who have changed their own, either generic or OEM.Maybe someone else can chime in about that.FYI: there are actually 4 O2 sensors in this truck. It seems only the 2 downline sensors fail with regularity. I've never changed the other 2.

[timmack]

yea the preheating thing is right. i used a long flathead screwdriver to snap the hard to reach clips in. you can either use a clothes hanger to snake the new wire up from the bottom or what i did was unplug the harness, tie a loose wire to it, pull it down and unhook the wire then hook it to the new harness and pull it up from the top. make sure you tie the other end of the snaking wire to somewhere, i used the hole in the dipstick handle.

[Chuck Tribolet]

I've had two O2 sensor failures on my '01 PF, a LONG time apart. Might have even been the same sensor. First failure occurred on warrantee, second at maybe 100K miles. I'd replace the dead one now and wait for the other to fail.The only savings to replacing them both now is jacking it up and putting it onstands (yawn).

[mvmcali]

does the 02 sensors have any effect on milage, performance etc OR are they only there to measure the before and after Oxygen on the cat convertors to make sure they are functioning properly

[Pwnin O'Brien]

does the 02 sensors have any effect on milage, performance etc OR are they only there to measure the before and after Oxygen on the cat convertors to make sure they are functioning properly

The upstream oxygen sensors have a huge impact on performance and gas mileage. The upstream sensors measure the fuel/air mixture and compare that to the mass oxygen sensors readings to ensure proper mixture. If those upstream sensors are reading improperly (but are functioning) then it can cause your vehicle to run lean or rich which will impact your vehicles performance and gas consumption.

[mvmcali]

thanks. that make sense.my car is showing the downstream 02 sensor is faulty. Is this sensor ONLY there to show if the CAT convertor is working properly. I.e. no value in replacing it other than to pass smog check

[Pwnin O'Brien]

thanks. that make sense.my car is showing the downstream 02 sensor is faulty. Is this sensor ONLY there to show if the CAT convertor is working properly. I.e. no value in replacing it other than to pass smog check

That's correct. Straight from the FSM: Under normal conditions the heated oxygen sensor 2 is not used for engine control operation.