Gumart1 Posted May 4, 2006 Share Posted May 4, 2006 Hey guys. I am replacing my main O2 sensors with Denso Universal replacements. The correct heater resistance is between 5.1 and 6.3 at 68 degrees. I am getting readings of 6.5 on the new ones which is less resistance than specified. My old sensors, original to the car to my knowledge, still give a reading of 6.3. I called a local Dealer and they verified that 5.1 and 6.3 range is correct, and it is also written in my Lexus Service Manual. I called Denso and was told by a tech that the reading I am getting is acceptable and that it is more important to check for proper voltage when installed. That doesn't sound right to me. Should I demand new replacements? Quote Link to comment Share on other sites More sharing options...
Ross W. Posted May 4, 2006 Share Posted May 4, 2006 Hey guys. I am replacing my main O2 sensors with Denso Universal replacements. The correct heater resistance is between 5.1 and 6.3 at 68 degrees. I am getting readings of 6.5 on the new ones which is less resistance than specified. My old sensors, original to the car to my knowledge, still give a reading of 6.3. I called a local Dealer and they verified that 5.1 and 6.3 range is correct, and it is also written in my Lexus Service Manual. I called Denso and was told by a tech that the reading I am getting is acceptable and that it is more important to check for proper voltage when installed. That doesn't sound right to me. Should I demand new replacements? Actually 6.5 ohms is slightly more than the specified range. But in any case don't worry about it. They'll be fine. Well within production tolerance. If they were showing 8 ohms or 3 or 4, I'd get them to replace them. My .02! Quote Link to comment Share on other sites More sharing options...
obergc Posted May 4, 2006 Share Posted May 4, 2006 I agree with Ross. Unless you have a fairly expensive DVM that you are using to measure the resistance with that can subtract the resistance of the electrical leads, you are undoubtedly reading a small resistance (.1 - .2 ohms) caused by the meter leads and if you subtract that lead resistance, you are in range on the high side. The voltage reading shifts as the sensor goes from a lean to a rich condition are of more importance, IMHO. Touch the meter leads together, take the reading and then subtract if from the reading you get through the sensor and see if that puts you in the acceptable range. Quote Link to comment Share on other sites More sharing options...
Gumart1 Posted May 4, 2006 Author Share Posted May 4, 2006 Thank you both . Curt, I did take a reading from the new sensor before I connected it to the harness. Same reading. I thought for sure it would change with the added length and the plug connectors, but it did not. I guess I was most surprised that the old sensors were just within spec while the new were not. One further question, the new universal plug has the same 4 colors as the OEM harness, Blue, White, and 2 Black. On the new sensor, blue is the signal wire, white is ground, and black are heater wires. I am assuming I'll be matching colors and lexls did it that way, but I want to be sure. Can anyone verify this? Quote Link to comment Share on other sites More sharing options...
Ross W. Posted May 4, 2006 Share Posted May 4, 2006 One further question, the new universal plug has the same 4 colors as the OEM harness, Blue, White, and 2 Black. On the new sensor, blue is the signal wire, white is ground, and black are heater wires. I am assuming I'll be matching colors and lexls did it that way, but I want to be sure. Can anyone verify this? Yes. Wire colors are the same. I did the upstream sensors last year. Really easy except the passenger side one. When you remove the old sensors, cut the original wires off at the sensor, and use a box-end 19mm wrench to get them loose. Save the old pigtails if your new sensors are not pre-loaded with the Toyota connector plug. Re-install with the included anti-sieze paste, only this time use an open-end wrench because a box-end won't allow the connector through. Remember to SOLDER the new and old wires together, and use shrink-tubing to cover the joints. DON'T use the supplied butt-splice connectors! Took me three times to learn not to do that! That applies only if your new sensors don't have the connector supplied. Quote Link to comment Share on other sites More sharing options...
Sweet95LS400 Posted May 10, 2006 Share Posted May 10, 2006 Now that you have your new sensors installed, any differance in performance or mileage? Quote Link to comment Share on other sites More sharing options...
Gumart1 Posted May 11, 2006 Author Share Posted May 11, 2006 Sweet - It will be difficult for me the judge the effects of the new sensors because I just completed a major tune-up at the same time. So I expect an all around improvement in mileage. I haven't driven the car yet. This was a fairly easy procedure for a do-it-yourselfer. Ross's suggestion to solder instead of crimping is right on. When I spoke to Denso Tech Support they agreed that the biggest problem they are seeing are people to don't crimp perfectly and having to redo the wiring later. Thanks Ross! One correction, it's a 22mm wrench for my '91, and after unplugging the connectors first, the box end fit right through the OEM harness. Same thing on the installation of the new; box end fits right over. I changed them because it didn't know the age of them on my car and assumed they were original. They were slightly rusted too. I also just had a crappy experience with stripped threads when changing the O2's on my '97 Ford Explorer. I got mine from Rockauto for about $50 each plus shipping. I prefer the Denso's to Lexls' Walker universals, Denso being OEM. But the tutorial helped a lot. One final note. The guys at Denso tried to talk me into replacing the 2 rear sensors. They claimed that the new fronts will change the chemistry of the airflow and that could throw the rears off. But I'm trusting the members here who say the rears almost never need replacing. Good luck! Quote Link to comment Share on other sites More sharing options...
Sweet95LS400 Posted May 12, 2006 Share Posted May 12, 2006 Let me know how it runs anyway. I would be interested to see how much of a differance there is after a full tuneup. Quote Link to comment Share on other sites More sharing options...
mann777 Posted May 25, 2006 Share Posted May 25, 2006 Could somebody let me know if the main O2 sensors are changed, does it have to be the sub sensors need also be changed, if they are not, what kind of performance implications can be seen. Does the sub sensors alter the ECT computer readings of the new sensors installed. Also does it also have any implications on the fuel consumption. Your thoughts Quote Link to comment Share on other sites More sharing options...
maxed_out Posted May 25, 2006 Share Posted May 25, 2006 anybody have the part numbers for the o2 sens replacements on a 91? A good source for the parts would be nice too. Quote Link to comment Share on other sites More sharing options...
mann777 Posted May 27, 2006 Share Posted May 27, 2006 check out on website sparkplugs.com website and choose the Denso link, which takes you to their website, once you input u vehicle details the OEM part number and the related cost is popped up. I have ordered from here and their service and technical knowledge is very good. cheers :) Quote Link to comment Share on other sites More sharing options...
ko90ls Posted May 28, 2006 Share Posted May 28, 2006 yeah i got mine from sparkplugs.com also. but i purchased the OEM sensors since i dont trust anything universal(personal issue). spent about 300 and all is well. but you may have to cut the grommet that the sub sensor is on but a little duct tape and there was no problems. i also noticed that my exhaust fumes smell different. they used to smell sweet-ish, but now there is no smell at all. i say why upgrade one component to 2000+ technology and leave the others in the stoneage (1990's) just MHO Quote Link to comment Share on other sites More sharing options...
mann777 Posted May 28, 2006 Share Posted May 28, 2006 U got a good nose man ! :P Anyway as said rite the exhaust emission standard has improved quite a bit, i have also observed on the smell. now regards mileage on a full tank these are the details With old sensors, my mileage on full tank was around 280 miles With my new sensors my new mileage is around 328 miles that is quite a improvement. Now recently i have filled once again and on the check, if this repeats to the figure even closely then that it, I thinks i would not be able to acheive more than that average. I should settle at that. Next i am looking at changing my sub sensors, but i need honest opinions from u guys since i have only replaced the main snsrs, and the old subs are still on the exhaust, do want to change it sometime soon as time permits just want to know whether there is any repurcussions on the ECT & will it change the readings for its performance Quote Link to comment Share on other sites More sharing options...
ko90ls Posted May 29, 2006 Share Posted May 29, 2006 shouldn't be any issues changing the sub sensor. the car has a built in O2 sensor override mode if for some chance they should fail. in fact when i when to change my sub sensors the passenger side wasn't plugged in! dash lights though. my suggestion use a box wrench and a rubber mallet. Quote Link to comment Share on other sites More sharing options...
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