My SES light finally came on and won't go off.

[Reelax]

ok guys, i need some info. especially techs.

i have a cali spec '99 ES V6 w/ 75K miles.

i replaced the 2 precats and the main cat w/ a MPHUnlimited downpipe w/ high flow cat.

a few months ago the high flow cat was replaced w/ straight pipe so now there are no cats (yeah i know how illegal this is).

the 2 o2 sensors that are screwed into the front manifold and top of the rear pipe are connected as stock, the 2 that are supposed to screw into the pipes downstream of the precats are connected to the harness but not screwed into the pipes... on the cali-spec this should "trick" these lower o2 sensors into reading flat (low voltage) as if the precats were present and working and thus not triggering OBDII SES.

after scanning the OBDII, the code that comes up is refferring to "o2 sensor bank 1, #2". now my question is, since this setup has not triggered the SES for 2 years, did one of the O2 sensors go bad? and if so which one? i will have my car up on a lift soon to inspect the lower 2 o2 sensors to see if one has been disconnected from the harness or is otherwise damaged (they both are currently just tied up and exposed). if it is not a fault in one of these sensors, could one of my manifold o2 sensors have gone bad causing the computer to think that one of the lower o2 sensors is giveing a bad reading? i have not had the chance to clip into the harness to read the voltages yet but if someone knows the answer then i won't have to.

last question, if it is just a faulty o2 sensor, will replacing it cancel the SES light? i know that the car is completely drivable w/ this situation but i hate it that i have a big orange light on my dash glaring in my face.

thanks guys... btw, the o2 sensors are $165 each so i don't want to have to replace all of them (4) if only one is causing the SES light and a dealership and most mechanics cannot help me here.

here is a pic of the stock vs. dp:




notice that the bungs for the lower o2's are ommitted for both the front and rear banks (on the AMSS unit, these bungs are relocated to behind the high flow cat). the lower bung for the rear bank on the stock pipe is not visible but there is one there.

any ideas?

[manybrews]

<div class='quotetop'>QUOTE(Reelax)</div><div class='quotemain'>
the 2 o2 sensors that are screwed into the front manifold and top of the rear pipe are connected as stock, the 2 that are supposed to screw into the pipes downstream of the precats are connected to the harness but not screwed into the pipes... on the cali-spec this should "trick" these lower o2 sensors into reading flat (low voltage) as if the precats were present and working and thus not triggering OBDII SES.</div>

okay, problem one. this should not be able to trick the ECM. the sensors are NOT suppost to read a flat no voltage reading. they are suppost to be around 300 to 600 continuous millivolts under the needed circumstances (warm, cruising, etc.etc).
your removal of the O2 sensors from the pipes should have indeed triggered a light a long time ago. there is the chance (however remote) that you just havent been able to meet the criteria for setting the codes. although thats unlikely.

<div class='quotetop'>QUOTE</div><div class='quotemain'>
after scanning the OBDII, the code that comes up is refferring to "o2 sensor bank 1, #2". Â*now my question is, since this setup has not triggered the SES for 2 years, did one of the O2 sensors go bad? Â*and if so which one?
</div>
well, the rear sensor failure is indeed quite common on the galants, but to buy a new one to test seems expensive.

<div class='quotetop'>QUOTE</div><div class='quotemain'> Â*i will have my car up on a lift soon to inspect the lower 2 o2 sensors to see if one has been disconnected from the harness or is otherwise damaged (they both are currently just tied up and exposed). </div>
damage is indeed the second highest cause of these sensor failures.

<div class='quotetop'>QUOTE</div><div class='quotemain'> if it is not a fault in one of these sensors, could one of my manifold o2 sensors have gone bad causing the computer to think that one of the lower o2 sensors is giveing a bad reading? </div>
no. they are MUCH more important, and are monitored seperately.

<div class='quotetop'>QUOTE</div><div class='quotemain'> Â*

last question, if it is just a faulty o2 sensor, will replacing it cancel the SES light? Â*i know that the car is completely drivable w/ this situation but i hate it that i have a big orange light on my dash glaring in my face.</div>
the light will have to be shut off. certain conditions CAN shut off the light if the problem disappears, but i dont think the O2 sensors are one of them.


incidently, im not sure where i last saw one, but have you thought about using a voltage inducer? There are products on the market that will fake a 500 MV signal to the ECM on "illegal" cars such as yours.

as i said, i dont remember where i last saw them.. i believe i came accross them when i was hot-rodding my camaro.

[Reelax]

thank you so much for your quick and detailed response... you're the man manybrews.

so from what i understand now, the top o2 sensors "pulse" up to 1v and the lower o2 sensors run a steady voltage of about .5v under normal conditions. so i could just get a .5v voltage source to send a steady signal to the ECM via the o2 harness. would this signal have to b variable to keep the SES from glaring again?

another route of action is that AMSS makes their gen1 downpipe w/ bungs for the lower 2 o2 sensors wich plug the sensors after a high flow cat. would this solve the signal problem?

here's a pic of the AMSS dp. i have been in contact w/ them to purchase and install just the rear section including the cat:



would this b a good solution?

again this is all assuming that my lower o2 sensors are not damaged... i really have to get under the car to check.

btw, thank you for ruling out the 2 top sensors, that leaves me w/ just the 2 bottom ones to worry about.

you've been a great help!

[manybrews]

<div class='quotetop'>QUOTE(Reelax)</div><div class='quotemain'>
so from what i understand now, the top o2 sensors "pulse" up to 1v and the lower o2 sensors run a steady voltage of about .5v under normal conditions. Â*so i could just get a .5v voltage source to send a steady signal to the ECM via the o2 harness. Â*would this signal have to b variable to keep the SES from glaring again?</div>
youre pretty much correct. the front O2 sensors bounce around from about 200 to 800 (give or take a millevolt) about 5 to 10 times a second. That is normal operation.
the rears, on the other hand, monitor what comes out of the catalytic converter. intially, the readings from the front to the rear sensors should match closely, as the cat. hasnt "fired off" yet. that takes a couple of minutes. After the cat. "fires off", it does its job by converting the unwanted gases into the good gases, so the oxygen level should stay pretty much close to perfect. At that time the rear O2s will stop bouncing like the front ones, and instead read a fairly steady voltage of about 300 to 500 MV (at cruise).
If the front and rear sensors match, the ECM knows the cat. has lost its ability to function, and triggers a code. You cant just unplug the O2s, as you will toss other codes in that case (the ECM is quite smart on these cars).
you also cant just plug in a .5 volt signal, because the ECM also monitors the O2 sensors heaters. All O2 sensors these days have a heater element in them to allow them to work almost immeadiatly upon startup.
Tricking the ECM is kinda complicated.

<div class='quotetop'>QUOTE</div><div class='quotemain'>
another route of action is that AMSS makes their gen1 downpipe w/ bungs for the lower 2 o2 sensors wich plug the sensors after a high flow cat. Â*would this solve the signal problem?</div>
yes, that is a much better solution.
I should tell you that removing the cats on todays cars is worth almost NOTHING in terms of performance. Maybe 1 horsepower, if that.
All youre really doing is polluting more, and making modifications difficult.
The cheapest route is to reinstall the factory cats. But thats obviously up to you.

<div class='quotetop'>QUOTE</div><div class='quotemain'>here's a pic of the AMSS dp. i have been in contact w/ them to purchase and install just the rear section including the cat: Â*

would this b a good solution?</div>
i cant tell you yes or no, as i havent personally dealt with that. i will say that i have traditionally had a lot of problems with aftermarket componants of any kind, but thats just a generalization.
<div class='quotetop'>QUOTE</div><div class='quotemain'>
again this is all assuming that my lower o2 sensors are not damaged... Â*i really have to get under the car to check.

btw, thank you for ruling out the 2 top sensors, that leaves me w/ just the 2 bottom ones to worry about.</div>
if theyre physically damaged, its pretty easy to spot. IF they have just failed, the only real way to test them is to reinstall them and test them whilst loaded.

you've been a great help!</div>

[Reelax]

ok here's more info...

the code the OBDII is returning is DTC PO141 [O2 sensor heater circuit malfunction (bank 1 sensor 2)]

after running through the service manual i found this...

13B-10 ...wire breakage and short circuit ... PO141

13B-144 - 13B-150 ...TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
[LIST]
[LIST]
[LIST]
i think that the rear O2 sensor either is damaged or the wire has been cut / disconnected. i have to get under the car to inspect...

funny thing is i am not getting a code for any fault in the lower O2 sensor for the front bank, DTC PO141 is just referring to the rear. can i assume that the front is operating normally since it hasn't been hooked into the pipe in 2 years and has not triggred the SES? i will get under my car as soon as i get the chance, it's always too dark by the time i get home! maybe this weekend i will get a chance.

thanks again maybrews!

btw, removing the main cat was not done for performance gains... the hi flow cat that was on the car simply cracked inside and was rattling so loudly that i didn't want to drive the car. i had the straight pipe put on as a "quick fix" since i could not get a hold of the AMSS rear section at the time of repair. i really don't like driving w/o the cat since it does spew pollution and it is a HUGE fine as well.

so my first course of action is to inspect and repair / replace the rear lower o2 sensor and if that is resolved, i will b getting the AMSS rear section, if only for the hi flow cat and rear bungs.

i hope when i look under there it is in fact a simple fix...

[Reelax]

ok. inspected the lower sensors... the rear bank lower sensor is not heating up, but the front one is working perfect. i'm going to replace the rear lower sensor.

as a quick fix to the annoying SES light, i removed the bulb in the cluster.
i'll reinstall it after i replace the o2 sensor and cross my fingers that the CODE goes away and the OBDII stays happy.

i'll let u know what happens after i replace the o2 sensor...

thanks again for your help!

[Reelax]

SUCCESS!!!

i went to the dealership and threw down $150.00 for the rear O2 sensor. i took it home and plugged it in and hung it behind the engine. disconnected my battery for 30 minutes, reconnected, fired it up and now my SES light is gone!

cali spec V6's do not need the rear O2 sensors in the pipe at all, they just need to be present and working including the heater circuit (at least as not to trigger the SES). now my next move is to get the hi flow cat and 2 rear O2 sensor bungs from AMSS).

thank you again manybrews for you info and expertise.