Not sure if this is the best forum for this question, but ECUflash is what I have used for all the monkeying around and this SES is the one thing I can't solve.

A search on evom for that code doesn't reveal as many articles as I would have expected. None of them conclusive. I some other car forums and sites I read that the 0031 is for the rear 02 sensor, so now I am just trying to figure out what to troubleshoot.

I am catless, hadn't had any problem for months. After first track day started throwing this SES. Have the Invidia, which relocates the front 02 sensor, did a good job of extending the wire and routing it so it doesn't touch anything metal (heat).

I have read that I might need to mod the rear 02 so its effectively sucked out of the direct exhaust path flow. I read that in a HowTo, so I only assumed it was to solve this.

JDMMAP sensor, ECUflash 1.35, GruppeS 3 port boost solenoid, LC wide band permanently in DP. catless.

Thanks for the help, to anyone with experience on getting rid of that code.

 

I didn't get a lot of bites on this post, but did learn a bunch by reading and jumping in on others. So for those that search and come accross this post because of the P0031 in the title. Here is was I learned so far to help you out in case you were like me, lost. The gurus will be bored to death, but please correct anything I messed up for the next reader.

The P0031 CEL, or SES, that I am getting started after 10 months of not having any CELs in this USDM evo 9MR. I had been modifying slowly and using EvoScan and ECUFlash to make the basic tuning mods. Those included the JDMMAP sensor, ECU Boost control, etc, which can all be easily search in the forums. I am not running a cat, and still had no CELs for a long period of time.

My first track day with the car and all sorts of little things came up. One of which was starting to throw this and other CELs. I eventually got all other physical things fixed, like struts, and alignment, from my first shake down day and began working on the CELs.

I couldn't figure out why I was getting this CEL. All information on this forum was geared towards folks that were wanting to remove their rear 02 sensor to use a WideBand in its place. I already welded in a bung to my DP for that WB. Others were getting the CEL because it was directly in the exhaust flow stream. ( mine wasn't ). There is a mod in the How Tos section to recess the o2 sensor out of the direct stream. Something that is a good first step, cheap, and solves many issues.

https://www.evolutionm.net/forums/ev...ouler-how.html

For me it seemed that the 02 sensor had failed. I had the behavior that the 02 sensor would throw the CEL only after 15 minutes or so of driving. I would clear the CEL with EVOScan and 15 minutes later it would return.

I learned that the 02 sensor doesn't fire up all of its tests right away. It takes time to 'ready' itself. Then if there is a problem with it, it will fail, and in this case fail the heater signal. A signal telling the ECU that the sensor is able to properly heat up. ~500 degrees.

I found out that the rear 02 sensor isn't needed for ECU calculations (which is what I originally thought). It is only an emissions tool, and the law in the US. It checks for itself, the cat, and compares to check for the front 02 working.

If you simply remove the sensor you will have two issues.
1 - the ecu will know the sensor is missing,
2 - the ecu will fail the heater signal test.

For 1 there are mods for the ECU to trick it into thinking the sensor is there. Those are generally called rear 02 simulators. tephra and mrfred both have them available, just search for 02 simulator.

MrFred's rear 02 simulator
https://www.evolutionm.net/forums/5353216-post148.html

For 2 options have changed over time. Initially you could plug in a resistor to trick that the sensor was using the current, which is covered here...

Removing your rear 02 sensor completed with resistor
https://www.evolutionm.net/forums/ec...heres-how.html

Or you could go with the more recent ECU version of tricking the ECU that the heater signal is appropriate and therefor not get a CEL.

MrFred's Rear 02 Heater CEL Fix
https://www.evolutionm.net/forums/6691277-post59.html

Since I had to assume/guess/deduce that my rear 02 sensor had just gone bad, AND since it doesn't seem to be necessary for anything other than emissions I applied the fix from the link above, MrFred's rear 02 heater cel fix. So far it has worked perfectly.

Based on what your goal is, you may need to consider and test that even if you apply a simulator and a heater CEL fix you may still fail emissions, depending on if its a continuous test that is checked for you or not. There is lots of debate on this topic, and not the level of detail I was intending.

Of Course thanks to the gurus and all others that share and provide info the posts.

M

 

Turns out that the P0031 may in fact be a front 02 sensor heater circuit issue. Based primarily on
https://www.evolutionm.net/forums/6749507-post20.html

This means that applying the rear 02 heater sim was likely an error, which I now need to undo. However it did give me somewhere to go as far as troubleshooting.

I got some help in the thread I was in for the rear 02 heater sim (though I got my hands slapped for asking too many questions about 02 sensors and pushing OT, so I am updating here) I do understand the importance of trying to keep the threads relevant and on topic though, so I don't feel too beat up.

At thread 167 of the link below acamus kicked in with some actual tests. Thanks acamus, fostytou, and krazykorean.
https://www.evolutionm.net/forums/ec...-patch-12.html

What I have found so far is that 2 things are likely.

1 - The 02 sensor is slowly going out of spec.
2 - The battery, under certain conditions, is not providing enough voltage and thats throwing the CEL.

Both are not the cheapest thing to replace, so knowing which one is bad is preferred.

Dealer front 02 sensor best price is 255 that I could find, so clearly you want to make sure its dead or dying first before you buy one, and its not the battery or something else.

I completed the tests outlined by acamus in the above referenced post, and also those provided by the FSM by kalpakiotis (see attached doc)

My sensor was returning a 6.2 Ohm reading for pins 1&3 and the attached doc specifies anything between 4.5 and 8.0. From that I gathered the sensor was fine. Some members state the reading should be 6.0 to 20. ?

Because of the above testing behaving as though the sensor is OK, I moved to the possibility that the battery was not providing enough current at times. Start up, or when the alternator was not running the electronics due to shudder or general crappy footwork. (Its a touchy beast with the HDSS clutch at times).

This would support the weird phenomenon of the CEL staying away until such a time that I shuddered the car on poor parking maneuver.

The Battery tests show that my battery is below 12V at 11.75, when the car is not running, ie no alternator.

I am waiting to see if someone can identify when and how often the ECU checks the heater circuit of the 02 sensor and if low voltage TO the sensor (below 12V) could throw the P0031 CEL.

Edit: Acamus also suggested purchasing a universal 02 sensor at This Link

I will replace the 02 sensor at that price, 35 bucks, and keep the current low battery to confirm that it was in fact a dying 02 sensor. I will report back.

M

I must be the only moron that is asking and answering his own thread. I hope someone reads this some day that can take a shred of use out of it.

 

good on ya

let us know if the front 02 replacement works.

i can never remember the P0xxx codes, but usually their description will tell u the problem

 

Still getting P0031. ?

Replaced the 02 sensor (with a new Bosch universal unit), New highheat wire, and new harness plug. Did this so that I could have two units to test/compare. And to have a spare that I know I could get home from the track with.

Replaced the battery as well.

Totally baffelled and out of ideas.

WOT behavior improved, and so I suspect replacinig the 02 was necessary either way. however as soon as I shut off the car, and started again, the code came back. If I clear it, the first start will keep it away, but then the next start will trigger it again.

Any ideas welcome.

Thanks

M

 

what kind of test pipe are you using? ive been using evomoto's test pipe and have never gotten a CEL.

im pretty sure you dont want to buy anything but $85 to permanently (we hope) fix the problem might be worth it

 

I am not sure of the brand. It didn't have any markings on it. The car was used when i got it so it, a year or so ago. I have the stock cat too. I had the test pipe on there for months, with no CEL.

On a couple threads ago I actually thought that P0031 was the rear 02, but later found out it was the front. Then my work has been on the front.

Do you think that code could be an issue related to the Test Pipe? It looks like one of the ultimate ones, where it looks like a small cat, even though its hollow inside.

I don't have any problem having to buy something to fix the issue. I am already several hundred bucks into NOT solving it As long as I can come up with logical or rational trouble shooting I will go down each path.

I could insert the cat, clear the code, and see if the behavior changes, but that would be saying that the code is a rear 02 error, wouldn't it.

 

Also to me the cell turned on again after 150 km from disable the Rear O2 sensor from the ECU.

I have 88840017 MAP version.....but this is not relevant.....I think.

I`m waiting to try tephra`s mod for my ROM and see if something is different about that cell.

Take care

 

I retested everything tonight. My new 02 sensor returns a 9.3 ohm on the pin 1&3 test. Voltage is fine. So I replaced my cat and removed the test pipe, to see if that would change the behavior. Nope.

The CEL came back on the second next start, just like every other time I clear it.

Do we have any way to find out what the engine checks to throw the P0031. I know that folks have figured out that the rear 02 only checks a couple of things, so is the info on what the ECU checks that would throw the P0031 available. Since I replaced everything I don't have any idea what is wrong.

M

M

 

Do you have a fried with same ECU?
If so can you try his ECU?
It might be problem within ECU as well.

 

Don't have anyone with an ECU that I could borrow. All my buddies are WRX and STI guys. my previous life. Anyone in SoCal want to lend me their 88590015 for an hour for a free lunch?

I guess I haven't gone down that path, because I didn't have this CEL for many months, until my first track day, and then it appeared. I had so many instances of the IC hoses blowing off, that the CEL didn't surprise me. Once I got all that buttoned down and other things fixed I am now stuck with this damned P0031.

Is there any logic to the fact that the CEL could be induced by having the Invidia 02 housing (which requires extending the wires a bit) ?

Something changed on the car, and I can't figure out what, and that something is causing the CEL directly or indirectly. At first it was an interesting challenge, and now I have just lost my mind.

 

Any luck with your ses? I just got this code... Ill try the new universal o2 and see whats up.

 

yeah im pretty sure its something with the front o2 becasue when i had the CEL on my car with no cat it was p0420 which is the rear o2 which can be fixed with the spark plug anti fouler

 

yes, I did solve the SES. After much work on everything it turned out to be a damaged wire in the harness. It was probably intermittent on the way out, so that made it even harder to troubleshoot. I had to run a jumper wire through the firewall from the ECU to the plug/connector over the valve cover. Since then No CEL. i did use the universal 02 and it worked fine.
M

 

Where was the damaged wire at for you? I don't think it is my o2 sensor because idle and everything is good. I have a wideband... I think I have a wiring issue too.