AFR stuck at 14.85

[maisonvi]

Ive done some searching and havent come up with a ton. One person had the same issue quite a while back, but the thread never came of anything. Rather than go necro on a thread that was close, I figured I would start a new one to see if anyone could help.

I did a log the other day and I checked it out and saw my AFR never moved from 14.85 (dont monitor AFR on the AP because I have an external AFR gauge). Obviously something was wrong, found the culprit pretty quick too (see attached picture).

No biggy, ordered a new O2 from rock auto, got it 3 days later. Planned to install and be hunky dory and back on the road. Installed the new O2 and still cant get my car to read anything but 14.85 (on the AP now).

Things I have done so far:
Reflashed my map
Unhooked the battery for 30 min
Unplugged and re-plugged in the sensor
Checked the sensor pins
Bench tested the new and old O2 Via this method: Driveway Diagnostics - Bad Oxygen Sensor - Jp Magazine

All my on car testing yielded no results. On the bench, I couldn't get the volt meter to work for either O2 so Im not sure if Im doing it right, or if both are bad.

Before I try and make a return to Rock Auto and get a new one (still not sure if the one I have is bad or if its the car), I figured I would see if any one else has any suggestions on what to check. My car hates me so its probably the most obscure thing possible.

[zjnspeed3]

I had this same problem before I blew up cus my car was originally hydrolocked which most likely fouled one of my sensors. I am built now so I just bought 2 new OEM O2 sensors for when I put it together this past weekend. If you are only doing this to the primary sensor, you might try doing it to the secondary one too.

[maisonvi]

Originally Posted by zjnspeed3 I had this same problem before I blew up cus my car was originally hydrolocked which most likely fouled one of my sensors. I am built now so I just bought 2 new OEM O2 sensors for when I put it together this past weekend. If you are only doing this to the primary sensor, you might try doing it to the secondary one too.

The secondary shouldnt matter I think for the AFR reading. The secondary is just there for cat monitoring so I shouldnt even need it.

[zjnspeed3]

Originally Posted by maisonvi The secondary shouldnt matter I think for the AFR reading. The secondary is just there for cat monitoring so I shouldnt even need it.

I guess it wouldn't hurt if you did it. I take it you don't have an AFR gauge?

[maisonvi]

Originally Posted by zjnspeed3 I guess it wouldn't hurt if you did it. I take it you don't have an AFR gauge?

It would only hurt as I would have to buy possibly replace a sensor that isnt bad/needed. If it comes to that I will do it I guess, but I would prefer not to waste the time/money/

I do have an AFR gauge I mentioned in the OP.

[zjnspeed3]

Originally Posted by maisonvi It would only hurt as I would have to buy possibly replace a sensor that isnt bad/needed. If it comes to that I will do it I guess, but I would prefer not to waste the time/money/ I do have an AFR gauge I mentioned in the OP.

Sorry I haven't given you much usefull information. I wouldn't worry about it since you have an AFR gauge but I know how it goes to make sure everything is running right. I hope you find the solution to the problem!

[maisonvi]

Originally Posted by zjnspeed3 Sorry I haven't given you much usefull information. I wouldn't worry about it since you have an AFR gauge but I know how it goes to make sure everything is running right. I hope you find the solution to the problem!

The gauge only tells me what the AFR Im hitting is. I need the primary O2 to read correctly to tell the ECU what to do. If its not reading right, the system doesnt know how to fuel properly. Letting it just be stuck at 14.8 could be terrible for the motor.

[zjnspeed3]

I know you are tight on money but did you try replacing with an OEM O2? Maybe the Rockauto one was for a normal Mazda 3 and not the speed 3? I know some things are switched on that website.

[maisonvi]

Originally Posted by zjnspeed3 I know you are tight on money but did you try replacing with an OEM O2? Maybe the Rockauto one was for a normal Mazda 3 and not the speed 3? I know some things are switched on that website.

The one I bought from Rock auto is an OEM O2 sensor.

[zjnspeed3]

Hm. I'm not sure then. Sorry again that I couldn't help you..

[HawkeyeGeoff]

Did you try the thingy-ma-bob @maisonvi; I heard that works

[Erick13Speed3]

Since you installed a new O2 and that didn't fix the issue is there something else that could be causing the issue? Have you tinkered with anything else recently that may be skewing your AFR's? Are the connectors themselves in good condition? Not too savvy when it comes to trouble shooting just thought I would throw some ideas. Hope you get it figured out.

[maisonvi]

Originally Posted by Erick13Speed3 Since you installed a new O2 and that didn't fix the issue is there something else that could be causing the issue? Have you tinkered with anything else recently that may be skewing your AFR's? Are the connectors themselves in good condition? Not too savvy when it comes to trouble shooting just thought I would throw some ideas. Hope you get it figured out.

Im going to pull my intake and battery and trace the wires next. It was also suggested to me to re-update my AP. I just ran an update recently and maybe something happened there.

[HawkeyeGeoff]

Originally Posted by maisonvi Im going to pull my intake and battery and trace the wires next. It was also suggested to me to re-update my AP. I just ran an update recently and maybe something happened there.

It could just be reading wonky on the AP for whatever reason. But this seems to be an isolated issue, so I don't think that would be it. Other people would have the same issue if it was a bug I would think.

I'm putting money on either A. Faulty replacement or B. wiring.

[phate]

Is it throwing any codes? I agree with Geoff on both points. Any way you could swap to a known good sensor from another car?

[maisonvi]

Originally Posted by phate Is it throwing any codes? I agree with Geoff on both points. Any way you could swap to a known good sensor from another car?

No codes. I had a code with the old bad one. Nothing with the new one. I hopefully will have a bit of time tonight to try and reinstall it and check the wiring.

[jomc111]

Did you get anywhere with this? @maisonvi;

[maisonvi]

Originally Posted by jomc111 Did you get anywhere with this? @maisonvi;

I got a 2nd new O2 sensor and had no luck with that either. So at this point I assume its in the wiring somewhere.

I pulled everthing out and tried to check contunity between the ecu connector and where the O2 plugs in, but I get nothing on any of the spots. Which means one of 2 things: either A: All 3 of the wires are broken/fried or B: Im doing it wrong. I tend to lean towards B.

So now I plan to un wrap all the wires and see if anything is broken anywhere. then maybe go about replacing them all. Yay...

[Jeff23spl]

I understand that your added AFR gauge works and read something that move when you change the engine running conditions. Then your OEM AFR from the oem sensor is pinned to 14.85 but you don't know when it quit working because you don't check it often?

If the AFR is really at 14.85 constantly, our LTFT/STFT are going to be maxed out on the low side and this should give a cell ? How reading of the added gage compare to the oem one ?

1 You can't mix speed and mz3 sensors because the speed use a wideband as the primary VS a narrowband for the mz3 and any secondary probes.

2- You can compare the value from Cobb AP with an OBD2 bluetooth dongle and Torque or another APP on your cell phone. That one could gives primary and secondary reading from the oem probes.

For the wiring, i would check critical region first. There isn't much current into that circuit to overload the wires so it must be a mechanical issue.
I would check around the exaust for burned wires. Then check if you have something that could squeeze the wire harness...(usually new parts install) You can also check for screw into the wire harness...(i did see that once...)
Then you could check all the connectors. start at PCM and look for loose or bent terminals. Check other plugs for the same thing...

Not sure if a fuse is used inside that circuit...It won't hurt to check them too.

[maisonvi]

Originally Posted by Jeff23spl I understand that your added AFR gauge works and read something that move when you change the engine running conditions. Then your OEM AFR from the oem sensor is pinned to 14.85 but you don't know when it quit working because you don't check it often? If the AFR is really at 14.85 constantly, our LTFT/STFT are going to be maxed out on the low side and this should give a cell ? How reading of the added gage compare to the oem one ? 1 You can't mix speed and mz3 sensors because the speed use a wideband as the primary VS a narrowband for the mz3 and any secondary probes. 2- You can compare the value from Cobb AP with an OBD2 bluetooth dongle and Torque or another APP on your cell phone. That one could gives primary and secondary reading from the oem probes. For the wiring, i would check critical region first. There isn't much current into that circuit to overload the wires so it must be a mechanical issue. I would check around the exaust for burned wires. Then check if you have something that could squeeze the wire harness...(usually new parts install) You can also check for screw into the wire harness...(i did see that once...) Then you could check all the connectors. start at PCM and look for loose or bent terminals. Check other plugs for the same thing... Not sure if a fuse is used inside that circuit...It won't hurt to check them too.

Yeah it was suggested to me to plug in an OBD2 bluetooth and test that. I have one that I loaned out, I will get it back this weekend.

From what I can tell via the shop manual there isnt a fuse in the line at all.

I am thinking about hooking eveyrthing back up and checking if Im getting any voltage movement on the wires when the car is running.

[Jeff23spl]

Originally Posted by maisonvi Bench tested the new and old O2 Via this method: Driveway Diagnostics - Bad Oxygen Sensor - Jp Magazine.

That test method is for a narrowband sensor while ours is a wideband with 5 wires. So you won't see voltage going arounf 0.5v like the narrow explained in the link above...


look at this info:
How 5-Wire Sensors Work (Tech Edge)

[maisonvi]

Originally Posted by Jeff23spl That test method is for a narrowband sensor while ours is a wideband with 5 wires. So you won't see voltage going arounf 0.5v like the narrow explained in the link above... look at this info: How 5-Wire Sensors Work (Tech Edge)

I will have to read that, but that's good to know how it's differnt. I'm checking the harness as specified in the shop manual.

Sent from my SM-G900V using Tapatalk

[570msp]

I had something short out on me awhile ago causing my car into limp mode and my AFRs to stay around 14. Check your eng bar fuse. It's quick and something to try. Just thought I'd throw in my suggestion

[mr.speedy3]

I had this happen to me before. My results were hopefully more painful than yours. Ended up being an ECU. Although with my issue, it would peg the AFRs ta 14.85 for a few minutes (5-10 IIRC) then start reading (among other issues).

I am told sometimes that the AP may not read back AFRs (instead it'll show 14.85) until the O2 is up to some internal temp.

Sorry if I missed it, but are your AFRs actually affected? As in, does the car actually function correctly outside of the AP not reading correctly, or does it stumble all the time, or maybe at just part throttle?

[Mazdazilla6]

@maisonvi; Did you ever find out what caused the damage to the first one? It kind of looks like heat damage. If that's the case then I would definitely be chasing wires. Heat causes resistance and excessive resistance can cause wires to burn up.

[maisonvi]

Originally Posted by Mazdazilla6 @maisonvi; Did you ever find out what caused the damage to the first one? It kind of looks like heat damage. If that's the case then I would definitely be chasing wires. Heat causes resistance and excessive resistance can cause wires to burn up.

It fell of its mounting and was resting on the downpipe for an un known amount of time.

I really have had zero time to look at this in the past 2 weeks. I just got to looking at it and I think I found the solution, a tiny break in the ENG BAR3 fuse. I couldnt really even see it but my meter says it not connected. I will get a new fuse and put it all back together. Hopefully that fixes it.

[Jeff23spl]

Good one. it is harder to find a broken fuse that isn't blown.

[Texasgunslinger9]

Just wondering did a new ENG BAR Fuse fix the problem? i have intermittent AFR stuck at 14.85 with P064D code.

[maisonvi]

Originally Posted by Texasgunslinger9 Just wondering did a new ENG BAR Fuse fix the problem? i have intermittent AFR stuck at 14.85 with P064D code.

Yeah, it had the tiniest of breaks in it. It looked fine holding it at arms length, but up close you could see that it had separated. Only way I found it was testing all my fuses with a multimeter.

[Texasgunslinger9]

Checked all my wires and fuses and everything was good. Found another discussion and someone said he replace spark plugs and that it helped him. I had I think about 20kish on mine. Replaced them and haven't had a problem with a stuck AFR at 14.85 or code p065d. I've seen a few other forums on SVT sites having similar problems and they are always followed with misfires. I personally didn't feel any large misfires, but it might have been small ones causing the PCM to think the o2 is malfunctioning. Just my opinion though. But I replaced spark plugs again with Denso ITV22 set at .028" and been running great with no problems. Hope this helps.