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Perhaps honda specific: Will a code 41 (o2 sensor heater) tank my mileage?

Based on the way the car runs/idles I'd say the o2 sensor heater code isn't affecting my fuel mapping, but then you never know, any ideas? Wanna know how much effort I should put into fixing it tomorrow.

Probably not. IME, heated oxygen sensors are just to make sure the cat's up to temperature and if it's not richen the mixture until it is.. It shouldn't impact your A/F ratio enough to do much to mileage.

The thing is, I think it's because of an old wiring trick I did to make my ecu (which wanted a 4-wire o2) accept a 1-wire o2. Now that I have the right 1-wire o2 ecu in there it's throwing the code...

What did you do to the wiring, and is there a change you mussed up your oxygen sensor? Too rich and it'll supposedly get sooty... Once I leaned out the AFM on the Camry to get rid of the obscenely rich A/F ratio, my rear bank oxygen sensor CEL turned off and hasn't come back on since.

Well, I recall doing some trick to bypass the heater so the ecu didn't throw a CEL, or mehbe I just turned the heater off on the chip I used, but I just went out and looked and it appear the heater wire is cut, so I'm going to hook that back up, poke around, and if it doesn't work, I'll forget about it until I get home from school.

My tracker has the O2 sensor heater code as well, from what I've read this is only important to get the sensor up to temp faster when the engine is cold. After the exhaust manifold gets warmed up (maybe 1 min) then the "heater" isn't important.
I have a scangauge and my tracker runs in "closed loop" mode all the time and I'm getting good mileage so I've decided not to bother replacing the sensor, the fact the GM stealership wanted $470, and suzuki wanted $320 for it also influenced my decision...

If the sensor fails completely then the motor will go into "open loop" and burn way more gas, maybe overheat the cat, and generally run bad. Then its time to get a new O2 sensor.
Ian

Quote:

Once I leaned out the AFM on the Camry to get rid of the obscenely rich A/F ratio, my rear bank oxygen sensor CEL turned off and hasn't come back on since.

roflwaffle, I am curious how you leaned out the engine? Its something I'd like to try.
Ian

Yes, it will affect MPG, it will not go in to closed loop (or is it open?) as fast. The ECU will throw extra fuel until the O2 sensor comes to temp. I don't know how much longer it will take/ how much extra fuel the Honda throws at the car to prevent driveability issues on warm up.

I just did some more reading on O2 sensors, to summarize:

Heated O2 sensors allow the sensor to be used for readings more quickly and allow the O2 sensor to be placed farther downstream in cooler locations in the exhaust.
Testing unheated O2 sensors requires the engine to be run at 2500rpm or so to provide a load to create enough heat so they work.

So, based on this, I would think that you are OK using an O2 sensor with a broken heater unless you;

like to warm up your car in the winter by letting it idle for 10 min:eek:,

or, have a huge engine running at very low load most of the time:confused:.

I'll assume neither of these conditions is true for you or your honda, the only other condtion would be idling in stop and go traffic for a long time. This may allow the exhaust system to cool enough so that an unheated O2 sensor would cool to much but I doubt it, maybe at -20.

That all said, if someone gave me a good O2 sensor I would like to try it out and see if there is any difference in my mileage, as I didn't find anyone else reporting about running with a failed O2 heater. I do have to think that since my car is running in closed loop mode that the sensor is reading within the normal range once the sensor is warm and that since I don't idle the sensor gets warmed up quickly enough not to worry about it.
Ian

This has nothing to do with the cat. The sensor needs to be hot to generate a signal. Exhaust heat will eventually heat the sensor up. The heater just accelerates this process and lets your car go into closed loop mode sooner.

I had this problem temporarily after I installed my Bosch gauge. The AEM gauge it came with was responsible for heating up the sensor, so I only used one wire on the old harness for narrowband emulation. To keep the ECU from throwing heater circuit codes, I chopped the harness off the narrowband sensor and soldered a 10 ohm resistor between the heater wires. Make sure it's rated for at least 10 watts though, or it will burn up. Also keep it clear of your wiring/looming, or it could melt them. Alternatively, you could wire a brake light bulb and socket in there to keep the ECU happy, if you don't mind your engine bay glowing for a few seconds on each start.

A 4 wire sensor is better than a 1 wire. I had a voltmeter hooked to my o2 sensor in my car and when it had a 1 wire anytime I did eoc, coasted in gear, or let it idle for about 30 seconds the sensor cooled off and took about 30 seconds to start reading again once I started driving unless I held it to the floor to heat it faster. With the 4 wire sensor it started working within 30 seconds of starting the car and stayed working while eoc or whatever.

The O2 goes high impedance when it isn't working so the computer knows to ignore it and just run off the fuel tables so without a voltmeter it is hard to tell when a sensor is working or when it is cold. It is easy to convert a 1 wire car to a 4 wire. And all 4 wire sensors are the same so go to a junkyard with a propane torch and voltmeter and get a few of them really cheap.

Here is a writeup I have on my site detailing O2 sensors:

Quote:

The factory one wire Oxygen sensor works well for what it was designed for but it does have limitations. 4 wire sensors have been used for a while so it is easy to find them at junkyards. It is easy to test a sensor to make sure it is working with just a voltmeter and propane torch. Take the sensor you want to use out of the car and hook your voltmeter up to the sensor wire and sensor ground wire using the chart on this page to figure out the wires. Once you have it hooked up you should be reading 0 volts. light the propane torch and hold the tip of the inner blue cone on the oxygen sensor. It takes a few seconds to get it up to temperature and you should see the voltmeter go to .9-1.4 volts. Once you get it there twist it around to make sure the whole element is heated evenly and any buildup on it is burned off. The voltage should drop within 1-2 seconds to under .1 volts when you take the propane torch away. If it does not go down quickly then try turning the propane up higher and burn off any deposits on the sensor you can. It will not hurt the sensor to make the case glow orange. After a few minutes of cleaning the sensor it should respond quickly to the torch being pulled away from it. If it is slow to respond to the torch being added or taken away then it is probably lead or silicon fouled and you can give up on it and go to the next one. If after 5 minutes it isn’t working like it should then give up on it and pull another one off a different car in the junkyard. I would grab an extra one while I am at the yard just to have a spare they are cheap.

Type 1 Type 2 Type 3 Description
Black White Black Heater Circuit
Black White Red Heater Circuit
White Grey Black Sensor Ground
Blue Black White Sensor Output

The Wiring is normally one of these colors. Make sure you only pick colors from one column. Things are much easier if you cut as much of the harness out of the junk car as you can to give you as much lead wire as possible. If not at least get the connector and a few inches of wire to splice into your existing harness. The connections should be pretty easy. The sensor ground should run by itself to a chassis ground and not just grounded to the engine in case the engine has a bad ground. The sensor output goes to the factory Oxygen sensor wire. The heater wires do not have a polarity so one wire should go to ground but not using the same wire as the sensor ground. The other wire should go to the ignition and only have power when the key is in the on position and not when the key is on accessory.

The advantage wit the new sensor is that the computer knows when the sensor is working and will use it to adjust the A/F ratio. The old sensor would cool off at idle and while coasting and take a few seconds to get back up to temperature. This left times when the computer could not adjust the A/F ratio. The new sensor has a heater so it will stay working at idle and as soon as you give it gas from coasting. It also heats up much quicker so it starts working much sooner when starting the car. The most obvious thing you will notice the idle is smoother and it doesn’t hesitate as much when going from coasting to accelerating. Overall this is a very simple and cheap mod so if you have some free time I would do it if your car has a 1 or 3 wire sensor in it now.

Quote:

Originally Posted by IndyIan (Post 23910)

roflwaffle, I am curious how you leaned out the engine? Its something I'd like to try.
Ian

Link. YMMV, but it should work as long as you can adjust the AFM on an OBD-I managed engine.

Thanks for the info guys, I guess I will have a look at getting another O2 sensor from the wreckers. So do all OBDII cars have the same 4 wire sensor, for threads and diameter?
Ian

i know this thread is old, but i recently replaced the clutch in my 95 civic hatch and one of the wires for the coolant temp sensor broke but i dident know it at the time. i drove around a little bit and my air/fuel gauge said rich and my check engine light came on. i fixed the coolant thing, but now i have a code 41 for the oxygen sensor.

sometimes the light is on, and sometimes its off, the sensor is fairly new. is there a way to clean it?( i think it got dirty from running super rich for about 20 miles). i might try reving it up pretty high and resetting the ecu.

update: i ran it around at high rpms today and reset the ecu and it seems to be fine now. i dont know that i really fixed the problem since it comes and goes, but im happy for now.