TOPIC: o2s

yes the rear o2s must switch as they are balancing the fuel trims. obd2 need to be switching regular as the front o2s are the coarse fuel trims the rears are fine tuning the ecu trims. obd1 early dumb ecus the rear o2s were for emission check only. If slow on not at all switching the cats going bad or 02s bad. Lazy o2s usually make the car get poor fuel mileage as they evetually go into dump fuel mode,or open loop. dan

I agree Dan. I ended up in a puddle down some back road that filled my Cherokee half full of water (yes, my rear end was wet when I was sitting). After 4 hrs when I got out, both my 02 sensors were cooked. I ended up getting 9 mpg with the 02 sensor reading 0 volts, and the LTFT at 32: to the max.

Take care,

Luke Wickenhauser
Gadgetman Saskatchewan

Hi Guys,

Before my trip to Madison, the night before to be exact, rechecked my O2s. The front sensor was flat at .4 to .6 volts, stuck in open loop. LTFT was also stuck at 22. This was going to be a long, expensive trip to Madison if I did not figure it out. I traced it down to some splices I had put in the O2 wiring for an EFIE I had used earlier. Just a small amount of resistance in the wiring created a big change in the O2. Simply pulling the spade terminals apart and reconnecting them brought the O2's back to life. The fuel trims dropped to neg and as I drove home, I could feel the surge in power.

Moral of the story is a little resistance makes a big differance in the O2's!

Scott Castleberg
Pellston, MI
Gadgetman Michigan

Could you break down what you are saying in more complete terms? Its a lot of good information, but assumes we all understand. I am trying to figure out what information I need to record off my scanner before a new mod, and being a newbie need it spelled out. Thank you for all your help and advice.

Hey, jbyrtus!! ONe tip I can think of-- If the vehicle is OBD11 and you have scan tool for that, watch the O2 sensor readings. ON any given O2 sensor data, after engine warms up, the computer should go closed loop, that is ECM starts using the various O2 voltage readings to actively change Ign. timing, fuel delivery curve etc.


I learned to watch 2 things on an O2 data readout: switching voltage up/down, how frequent the up/down switching is. How often switching happens is called cross-counts. You want to see the voltage readout switch through a meaningful range within a total range: if total range is one volt then going from say .375 to .859 is meaningful .375 to .420 isnt so meaningful.


How often the up/down switching in voltage value happens is just as important (i'm not expert in this stuff others on this forum know lots more than I). If the O2 reading switches only say every ten seconds, give it some gas and watch closely..it should respond to that and quickly. If you are opening/closing throttle w/ engine all warmed up and the readings dont change much then this O2 is either old/worn(Lazy) or shot. Dont forget wire plugs and connectors any resistance on the O2 wires will mess up readings too.


Age and miles on vehicle are a big clue. If over 60K mi. O2's are likely lazy or about done. Nothing absolute here, that's why you're checking w/ scantool...


I assume you have/will do homework here I dont know your experience. Easy to look on Net do searches like checking for a bad Oxygen Sensor for example.


Judging this stuff is sometimes easy others murky. My bottom line: Check O2 values w/ scantool. If known that O2's have over 60 K miles I'm just looking for info that allows me to condemn 'em. But I'm going to verify the wiring connections are OK.


Visual: You're the Roman Emperor--the crowd holds its breath as you stand up...will you allow the O2 to continue life or will you give Thumbs Down and send it to the trash can...?



Good Luck
search this site and the youtube videos thouroughly
TracyG Gadgetman Reno

To add to this discussions, there are 4 different types of oxygen sensors:
- Narrow Band (NB)
- Titania
- AFR
- Wide Band (WB)

The NB is the most common, and is used exclusively for '96+ DS sensors. It generates an extremely low amp voltage that typically ranges from 0-1 volt. Low voltage is lean while high voltage is rich. Expected lifespan is 6 years or about 90k miles (optimistically).

The Titania sensor was used only for about 3 model years on extremely limited applications (I know Jeep used them) from about '89 to '91. They work similarly to the NB except the voltage is reversed; low voltage = rich. They too are a 0-1 volt output sensor.

The AFR sensor is used on many Japanese imports; Honda and Toyota are the 2 I'm most familiar with. They act as a variable resistor. When the exhaust is lean, they have low resistance. When it's rich, they have increased resistance. Most types are of the 4 wire variety, but I have seen a few 6 wire AFR sensors (a Hyundai comes to mind). Usually there are 2 "signal" wires that maintain about a 0.3 volt difference. On Toyotas, you will find 3.0 and 3.3 volts on your signal wires.

The WB O2 is probably the least understood of the various types. There are 6 wires leading from the sensor to the connector, but only 5 wires leading back to the ECU. At the connector there is what looks like a capped plug. This is the "calibration resistor". Since manufacturing tolerances vary widely, the calibration resistor is laser etched to bring the sensor into calibration. The WB has a NB built in. It uses Yttrium Oxide substrate to "pump" ambient air into and exhaust gas out of the sample chamber. Yttrium Oxide will pump oxygen ATOMS in one direction when one polarity is applied, and in the other direction when the reverse polarity is applied. The ECU will work the pump to maintain a 14.7:1 AFR in the sample chamber. It monitors how much current, and the polarity needed to do so. The WB is the most temperature sensitive of the bunch. (Don't put resistors in the heater circuit on these babies!)

I don't want this to get too long, but at least you have an idea of what you might be working with now.

Mike

Hi Mike
thinking about your last post about sensors, I own a 2004 toyota sienna minivan with 249000 kms and have checked into replacing these sensors but they are pricy, so I am wondering which type of sensors they are (assuming afr sensors) and what your take is on their life expectany is.
Thanks Aaron

Check the color of the wires coming out of the sensor itself. If you have either a green or blue wire, you have an AFR sensor. If it's 5 wire (or 6 wire) you most likely have a WB. Your post-cat down-stream sensor will be a NB. Fortunately, the AFR sensors are a bit more durable than the NB and last longer. I have only seen maybe 2 of these go bad, even with lots of miles (kilometers).

Hope this helps,

Mike