carwilef7 Posted August 29, 2009 Share Posted August 29, 2009 Does anybody know if a downstream O2 sensor (left side, after the converter) could seem to test okay with a voltmeter but just be lazy enough to set a P0156 code (0708 with the screw-turn method)? The FSM code explanation hints at slower response time than expected. Heater resistance, B+ voltage, and running voltage readings seem okay. I wonder if maybe all those flood-start attempts prior to coolant temp sensor replacement might have damaged it. Can't think of any other reason only the left one would do it. Any ideas? No running/idling problems, since it only really measures cat efficiency, but I doubt it will pass VA inspection that way. Link to comment Share on other sites More sharing options...
LostNcrRanger Posted August 29, 2009 Share Posted August 29, 2009 My frontier used to do the exact same thing. i could never figure out why. has it been submerged lately? Link to comment Share on other sites More sharing options...
carwilef7 Posted August 29, 2009 Author Share Posted August 29, 2009 My frontier used to do the exact same thing. i could never figure out why. has it been submerged lately? Not that I'm aware of, but I've only had it since April, so who knows? The flooding to which I alluded had to do with fuel dumping on hot start-up - now apparently fixed. It would get a crazy-high value from the Coolant Temp Sensor, go into "WTF?" mode, and flood out. A new CTS fixed that problem, but this problem may have been a result of that one. Link to comment Share on other sites More sharing options...
LostNcrRanger Posted August 29, 2009 Share Posted August 29, 2009 i think the inner jackets on my wiring got wet,causing it to short out. but what do i know. if you go to auto zone and have them clear it,see how long it will stay off for. you could always sneak in,clear your code,and run it through inspection that way before the DTC light comes back on. Link to comment Share on other sites More sharing options...
carwilef7 Posted August 29, 2009 Author Share Posted August 29, 2009 (edited) Autozone here is useless - they can read the codes (incorrectly) but they can't clear it. They got sued for clearing them or something. I can read it out and clear it myself with the screw on the ECM. The SES/MIL light will come back on on the 2nd or third drive after that with the same code. Unless it stops acting up or is replaced, it'll probably keep coming back. I think you have to have a number of driving cycles with no probs to pass. Inspection isn't due until next April, so I guess I've got plenty of time to figure it out. Just wanted to see if anybody had any other possible causes before I spent $90 on the sensor. Edited August 29, 2009 by carwilef7 Link to comment Share on other sites More sharing options...
adamzan Posted August 29, 2009 Share Posted August 29, 2009 Well if your truck was flooding out, it probably burnt all that fuel at some point. Could the sensor just be fouled? Link to comment Share on other sites More sharing options...
carwilef7 Posted August 29, 2009 Author Share Posted August 29, 2009 Well if your truck was flooding out, it probably burnt all that fuel at some point. Could the sensor just be fouled? It's a decent bet. Dunno if there's any way to successfully clean one. I'll try to pull it this evening and see. Link to comment Share on other sites More sharing options...
westslope Posted August 29, 2009 Share Posted August 29, 2009 (edited) Can't help you carwilef7 but if I may sneak in a related question. Your O2 sensor is downstream of the cat converter? Mine ('93 pathie) is upstream of the converter. Why the difference? Could somebody please explain. Edited August 29, 2009 by westslope Link to comment Share on other sites More sharing options...
SilverPath Posted August 29, 2009 Share Posted August 29, 2009 The R50s have 4 O2 sensors, 2 precat and 2 postcat. The one he is talking about is 1 of the sensors after one of his cats. The WD21 only has 1 sensor if I'm not mistaken and its precat. Hopefully that helps Link to comment Share on other sites More sharing options...
LostNcrRanger Posted August 29, 2009 Share Posted August 29, 2009 The difference has to do with OBDI/II electronics iirc. Link to comment Share on other sites More sharing options...
carwilef7 Posted August 29, 2009 Author Share Posted August 29, 2009 The R50s have 4 O2 sensors, 2 precat and 2 postcat. The one he is talking about is 1 of the sensors after one of his cats. The WD21 only has 1 sensor if I'm not mistaken and its precat. Hopefully that helps Exactly. Two cats, two pre sensors, two post sensors. A set for each bank. Link to comment Share on other sites More sharing options...
Channel595 Posted August 29, 2009 Share Posted August 29, 2009 all the post cat sensor does is to test to see if the cat is working, if your car was running rich for a long while you could have burnt out your cat could be expensive test the o2s before you do anything or you can go under it and beat on your cat with a fist to hear if the inside material has broken loose it will rattle around in there Link to comment Share on other sites More sharing options...
carwilef7 Posted August 30, 2009 Author Share Posted August 30, 2009 Hope it's not the cat - don't think so. Last few days, ever since I found the @#$%$^&* reset screw on the computer, I've been reading it out and resetting it every time the MIL light comes on (same code every time). After each reset, I've kept track of which trip I was on when the light came on again. Something like this: 1st reset - 2nd trip 2nd reset - 2nd trip 3rd reset - 2nd trip 4th reset - 3rd trip 5th reset - 6th trip (!!!) All the trips were about the same for speed and mileage. If that trend continues, it could be that whatever is in there might just need time to cook off. Link to comment Share on other sites More sharing options...
westslope Posted September 1, 2009 Share Posted September 1, 2009 Thank you SilverPath and carwilef7 for the detailed explanation. Appreciated. Link to comment Share on other sites More sharing options...
Precise1 Posted September 1, 2009 Share Posted September 1, 2009 If the O2 sensor isn't rusted in place, go ahead and pull it. 'clean' it by getting it very hot with a torch. While it cools, pull the other O2 and install it in the first bank. Next install the 'cleaned' O2 sensor in the other bank. If the problem goes away, you cleaned the O2 sensor sufficiently. If the problem switches to the other bank, replace the O2. If the problem stays put, you have an issue with wiring, cat, injectors, etc but you at least know what side to look at/swap out. B Link to comment Share on other sites More sharing options...
carwilef7 Posted September 1, 2009 Author Share Posted September 1, 2009 (edited) If the O2 sensor isn't rusted in place, go ahead and pull it. 'clean' it by getting it very hot with a torch. While it cools, pull the other O2 and install it in the first bank. Next install the 'cleaned' O2 sensor in the other bank. If the problem goes away, you cleaned the O2 sensor sufficiently. If the problem switches to the other bank, replace the O2. If the problem stays put, you have an issue with wiring, cat, injectors, etc but you at least know what side to look at/swap out. B Good idea on the torch-cleaning. It occurred to me to switch them - trouble is I don't think the wires are symmetrical in length. In other words, the right sensor wires won't reach the harness if it's in the left pipe. Also not big on pulling anything just yet for fear of breaking rusty pipes. Dunno how old they are - truck has 149K. Seafoamed it today and blew tons of crud out the exhaust. Runs like new, not that it ran bad after my initial going-over to replace filters, plugs, wires, cap, rotor, etc. When I first got it, the plugs looked like they'd been in there since Nixon was president. Anyway, I'm gonna run it a few days, reset the ECM again, then see if I still get any codes. If I do, I might try to torch-clean the one that's acting up - and attempt a switch - before replacing it. Edited September 1, 2009 by carwilef7 Link to comment Share on other sites More sharing options...
Precise1 Posted September 2, 2009 Share Posted September 2, 2009 Fair enough, I just went down the ideal trouble shooting/process list. If it isn't feasible... The torch 'cleaning' is plagerized (from 88pathoffroad I believe), but how much of info isn't?? I haven't done it myself, so let us know what you achieve. Good luck... B Link to comment Share on other sites More sharing options...
carwilef7 Posted September 2, 2009 Author Share Posted September 2, 2009 Will do! Thanks for the ideas! Link to comment Share on other sites More sharing options...
carwilef7 Posted September 2, 2009 Author Share Posted September 2, 2009 Precise1 - Sorry - didn't mean to blow you off. You had no way of knowing the pipes weren't in ideal shape. I guess I'm bad about asking questions and then dwelling on them and winding up on a whole other trip when someone does reply. I'm still interested in those hub center caps, btw. Tomorrow, I'll try to post a pic with the one I have and some rulers so we can see if they match before we negotiate. Link to comment Share on other sites More sharing options...
Precise1 Posted September 2, 2009 Share Posted September 2, 2009 No worries, I didn't realize you had... This is why I said "If the O2 sensor isn't rusted in place". I hate exhaust work due to the rust corrosion that is inevitable. Sorry, I need to get my butt in gear with the part out thread, ther's just so much to do right now... B Link to comment Share on other sites More sharing options...
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