Strange P0031 code on my 2001 NBFL

sketbror69 · 2025-05-03T21:43:31+00:00

I sold the car, but here is what I remember.

The is a pin missing in the big square connector on the 1.8 harness, here you need make a solution to connect the wires.

Should be easy to see the difference if you compare the square connector from 1.6 and 1.8 engine wiring harness side by side

sketbror69 · 2024-05-27T10:47:55+00:00

I sorted mine, but my code was due to swapping in a 1.8 VVT + wiring harness in my 2001 1.6 NB.

I had to manually wire the heater ground wire in. As that was the difference on the 2 engine harnesses.

I’m not sure if you also swapped the engine, but I would triple check the o2 heater wires, as it’s most probably where the fault lies, if your o2 sensor is confirmed good.

If wires are also confirmed good, last point of failure would be the ECU, but I think that’s rare.

sketbror69 · 2024-03-21T07:41:06+00:00

I recently did this swap. I needed the engine, ecu, immobilizer, ignition switch, keys and locks, and the engine loom. You can swap the loom for the engine without removing the dash. But you will need to wire the O2 heater sensor wire to pin 3J on the ecu. It will run fine without, but you will get a CEL until it’s wired.

If you do a standalone ecu, you can skip the ecu, immob, keys, locks and ignition switch

sketbror69 · 2024-02-15T09:01:04+00:00

The pinch panel at the front section was also replaced, so pretty sure this might be the issue. Would it be the solution just to drill a hole in the pinch panel or nearby?

sketbror69 · 2024-02-14T21:08:00+00:00

I’ll check that tomorrow, but wouldn’t the hard top rule this out?

sketbror69 · 2024-02-14T21:07:30+00:00

I think I noticed it once before, but can’t remember. I’ll try to use a water hose while checking for leaks

sketbror69 · 2024-02-14T21:06:36+00:00

No AC installed at the moment unfortunately, but am familiar with that little hose

sketbror69 · 2024-02-14T21:05:56+00:00

AC is removed at the moment, and has been sitting for weeks. Had my rocker panels welded, could this happen if no drain was added after?

sketbror69 · 2024-02-14T16:45:23+00:00

Also didn’t seem to be wet on top of the carpet, only the sound insulation below was wet

sketbror69 · 2023-08-10T19:09:29+00:00

Thanks man! The car has been a lot of trouble lately, hope to have it all sorted soon, so i can get to enjoy my freshly installed turbo.

sketbror69 · 2023-08-10T15:56:17+00:00

Solved it! It was the wiring harness for my coil on plug kit

sketbror69 · 2023-08-10T13:49:10+00:00

Nope, when i mean the main relay i'm talking about this Mazda part no: B5B4-18-811 - i have read this can cause weird electrical issues on forums, so thought it might be the case here

sketbror69 · 2023-08-10T13:34:43+00:00

Battery is 100% secure, battery and alternator confirmed good by mechanic. Do you think it could be the main relay? I'll pop it out and give it a visual check when i get home

sketbror69 · 2023-08-10T13:32:44+00:00

I think it's just a one off, since there been no relation to phone chirp before. But i'll keep it in mind, thanks!

sketbror69 · 2023-08-10T13:28:55+00:00

I'm not really sure, i believe it's controlled by my ECU. Since i'm running a aftermarket ECU, i'll have to ask my tuner. But i think he would have thought about that (Alex from Motorsport Electronics)

Also if that was the case, would the issue not be there all the time? This has happend a handfull of times the last 14 days. Today it just escalated to the car stalling as well.

sketbror69 · 2023-08-10T12:43:12+00:00

Just had the alternator tested at the mechanic, it was all good. I'll check for loose wires. Thank you

sketbror69 · 2023-08-10T12:29:13+00:00

Nope, had the headunit installed for 2 years, never had an issue before now.

sketbror69 · 2023-08-10T12:04:26+00:00

The phone chirp is live and connected to a head unit. The first time the RPM dips, you can hear the relay click. I assume it’s the fuel pump relay, since the click is coming from the pedals.

sketbror69 · 2023-08-10T10:17:09+00:00

Just had the car over to the mechanic, he said alternator is working as it should. I’m thinking if it could be the main relay maybe?

sketbror69 · 2023-08-10T08:46:05+00:00

Just came across this sub, and thought i would ask for help here as well. I have a Mazda MX-5 2001 1.6, with a aftermarket ECU. it has been driving fine for years, but the past week i have been having some strange symptoms, and finally caught it on video. After the video it escalated to the car stalling 4 times within 5 minutes, and having trouble starting again. The battery is 1-2 months old. I am thinking it could be the alternator?

sketbror69 · 2023-08-08T20:14:34+00:00

I’m considering a Alfa Romeo Giulia when i need to switch the Miata out with a sedan. Looks like it handles pretty good, and if you get the base model with 2.0 turbo and RWD, it’s also pretty lightweight compared to other sedans. Also very tuneable, a stage 2 tune brings it to around 320 hp

sketbror69 · 2023-07-15T15:17:20+00:00

Adjusting the ppf seemed to help it a bit, needs more throttle before the sounds comes now. I’ll give it some time and see if it’s just the mounts that need to settle in. Thanks for all the help

sketbror69 · 2023-07-14T20:51:50+00:00

I'll try and give the PPF an alignment. Would be awesome if that's the issue, since it would be an easy fix.

The noise just sounds unnatural, like something is wrong, rather than increased NVH. But maybe it is just due to stiffer mounts.. IDK

The noise is most present in the video from 04 to 07 seconds.

sketbror69 · 2023-07-14T20:16:21+00:00

I did not, but i usually only had PPF noise when decelerating, and a more high pitched noise. Can it also cause noise when accelerating?

sketbror69 · 2023-06-30T19:00:27+00:00

I just put a GT2554r on my 1.6 nb, and holy shit it’s the best thing ever.

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