r3fuj33

I'm looking to replace the secondary O2 sensor because it's probably overdue to be changed out and I'm wondering what all is involved. Does the front bumper need to come off or anything like that?

xRiCeBoYx

iTrader: (22)

Ex: jack up car, get under the car, disconnect sensor, unscrew sensor, install new sensor, put at back on ground.

I'd imagine the dx/lx is similar, I'm not 100% sure the exact placement of the post-cat sensor.

04 Honda Civic

iTrader: (2)

Front bumper does not need to come off.

However if your doing secondary why not primary as well?

You will need one of these http://www.samstagsales.com/SirTool/st4491b.jpg

Other then that its pretty much what Riceboy said.

xRiCeBoYx

iTrader: (22)

I just use an open ended wrench on mine

ezone

I wait until they are actually an issue.

gearbox

iTrader: (95)

true, secondary sensor has no real effect on how the engine runs. but on the ex, its the one inside the cat converter.

04 Honda Civic

iTrader: (2)

Good idea, however they are not always that easy. In the cat you cant use an open end as the heat sheild to the cat is in the way. (Dont ask me how I know this )

04 Honda Civic

iTrader: (2)

New ones help improve mpgs no?

ezone

Only if the old ones had problems.

(Obviously, if the old ones were still working perfectly, then new ones wouldn't be any improvement. Correct?)


An O2 sensor has to be skewed quite a bit to throw mileage off but yet not turn on the CEL, and that isn't easily detectable without some specialized equipment. Without that, it's just a hunch.
Most common O2 sensor faults can be detected by the PCM, but every so often I get to diagnose one that doesn't.

Have chased a couple like this on 6th gens (actually was bucking once in a while due to going excessively rich, not a gas mileage complaint).
I don't think I have chased something like this on a 7th or newer.

No-code driveability diagnostics are a challenge.

gearbox

iTrader: (95)

i thought the sensors age over time and lose their response time. ideally, replacing them every few yrs would be better than waiting for the engine light to come on, which varies between 80-120k miles. by that time, the sensor is nowhere near as accurate as new.

ezone

Agree, but

Try selling that to a customer that has no complaints about it.
At regular shop prices with factory parts. (Price the sensors plus labor, and then figure the ROI on fuel savings at, say, a 1MPG improvement.)
I think California BAR (or something like that?) would hang you for overselling there, while most other states don't have the oversight.



From what I have seen in general, as a sensor (O2, LAF, etc.) ages it tends to develop a slow response time more than anything. There are codes that cover this aspect on most of these.
O2 sensors are heavily scrutinized because so much of the emissions systems are dependent on them.
Random 04 Civic: P0131 through P0147, and P1157 through P1164 are all O2 sensor related.

(Seems like I see heater codes rather consistently.)

The computers have steadily gotten smarter over the years...The sensors have improved a lot too.....Of course, sometimes situations come up that the engineers didn't think of ahead of time. No code diags are fun.

HTH

gearbox

iTrader: (95)

just thought of a random idea. would turning the car to ON position for 20 secs or so to warm up the sensor be useful for any reason? like in the winter before starting the motor? the 20 secs is how long it takes for the sensor to reach full heated temp.

ezone

No. When I said response time, I meant the time in milliseconds to transition its output voltage from roughly 1v to 0v to 1v (sensing rich to lean to rich, and the speed of its reactions). This is what normally becomes slower with age.

Something like this is real apparent when looking at (example: something GM) with an unheated sensor that is 20 years old. Around .5 to 1.0 seconds or more to transition, and/or not have a full range of voltage during the checks. Referred to as slow and lazy, skewed or biased, at that point. A common cause of slightly rich or lean running, and fuel trim numbers a little out of whack. Or a lot.




OTOH, you are talking about "time until active", 20 seconds is about average for a heated sensor nowadays. That seems to stay pretty consistent, barring ambient conditions, unless there is a failure of the internal heater. Then it sets a code for the heater.

You would need to check a wiring diagram to see if turning on the key would power up the O2 sensors, or if their power is only on while the engine is running. AND consider whether or not the PCM controlled ground circuit is complete during the same conditions.
I feel lazy at the moment LOL.

gearbox

iTrader: (95)

i already looked it up a while back in the honda elec manual and the heated sensors do become active in the ON position. along with quite a few other things. i see battery voltage drop from 12.8v to around 12.0v turning from off to on. after the fuel pump kicks back off, voltage rises to around 12.2v but i can tell there is quite a bit of "stuff" drawing power with engine off. if left like this for too long, can easily drain down the battery.