Codes P0130 and P0031 [Archive] (2024)

Chuck H

30th August 2017, 07:50

As some folks might remember, I had an "incident" a year or so ago where one of my O2 sensor wires worked loose from where I thought I had secured it after installing a header, melted through insulation somewhere, and shorted, blowing the 15A ECU fuse and killing the car at 70 mph on the highway.

Had it towed to a dealership (since I had no idea what the problem was), and they replaced the fuse and secured the wiring better. It's been running fine since then, but I've had the CEL on almost continuously for several months now. I need to get it cleared up in the next couple of months because I have to go for annual inspection/emissions test.

Pulled codes last night, and it's showing P0130 and P0031. I cleared them last night and the CEL was back on this morning after less than 2 miles of driving. Just wanted to double-check before I dive into trying to fix this sucker -- those codes refer to the front O2 sensor, correct? And should I try looking for loose connections, or do you think I should just bite the bullet and replace the front O2 sensor and the extension cable (I have the PPE long tube header, so extensions on both sensors)? I remember the mechanic saying that the connector (where the sensor pigtail meets the extension cable, I assume) partially melted, so I suspect that it will always have intermittent contact issues.

I also have access to all kinds of wire, crimp connectors, soldering irons, etc. at work, so if I do get a new sensor and extender cable, would it make sense to splice the extender to the O2 sensor pigtail basically giving it a really long pigtail and eliminate one connector in the circuit?

Ted928

30th August 2017, 19:36

Chuck H

8th September 2017, 21:49

Well, finally got under the car tonight, planning to remove the O2 sensor and extender and splice them into one long O2 sensor harness. But when looking at it, I realized it was my rear O2 sensor connector that touched the exhaust and caused my problems last summer. The front sensor and its connector look perfect. I pulled the heatshield off by the header so I could get to the other end of the extension and that connection felt a little loose, so I mated it better, restarted the car and the CEL was gone.

Unfortunately, my joy was short-lived. I re-started the engine twice -- no CEL, then decided to take a short ride and before I could even back out of the garage, it was back on. Pulled codes, and now it's throwing P0130, P0054, and P0134.

I hate to just throw money at it shotgunning the problem, because the front O2 sensor is $300, and mine only has 30,000 miles on it. Maybe I'll try the splicing thing after all and hope that fixes it. Otherwise, I'm stumped on this one. :ohno:

EDIT of EDIT: Just realized that I basically have nothing to lose hacking up my front O2 sensor if it's not working anyway. If the connectors on the extension harnesses are suspect, would it make more sense to cut the connector off the OEM sensor and splice wires in there to extend it long enough to reach the engine bay harness without the extension harness? That's assuming that the OEM sensor connector is higher quality than the ones on the extension cables.

fastredrat

9th September 2017, 08:20

OEM Denso A/F O2 sensor is available for under $150 at many online distributors.

One example :
https://www.autopartskart.com/mazda-mx5miata-2012/air-fuel-ratio-sensor.html?partno=np2349093&utm_source=google&utm_medium=shopping&utm_campaign=mazda&prodid=802829201210328np2349093&gclid=CjwKCAjwos7NBRAWEiwAypNCe5beDZFCfvBxG-arD-roE9-2AeEFG1CB_q1HmHjPLfF29J6f4bZ82xoCMEwQAvD_BwE

MikeF

9th September 2017, 09:50

If you can, pin check the harness from the ecu to the connector to check resistance, open or short to ground. Plug Ecu back in and check for voltage at the "heater" circuit at the sensor connector when cycling key on.

Typically the "sensor" wires are shielded, to keep outside sources from adding signals from adjacent wires and influencing the signal that the Ecu it seeing.

I would avoid changing anything on the factory harness if you can and focus on the extended harness. Hopefully that is where your problem lies. Also the AF sensor might not like all the vibration that the header is potentially going through (possibly).

Chuck H

9th September 2017, 18:38

Well, went to all the trouble of lengthening the original sensor and removing the extender cable, and no luck -- same codes: P0054, P0130, P0134. So either the original sensor is completely dead after 32,000 miles, or I've got a problem in the engine harness.

Luckily, I didn't hack up the extension cable, so I guess the next step is to order a new sensor and try it with the extension harness. If the codes don't go away, then it may be a trip to the dealer to figure out what the heck is wrong with the harness. :(

I wonder if Mazda could have made those O2 sensor plugs in the engine harness any less accessible, if they put their top people on it. It took me hours to swap the stupid sensor because I had to pull the header heat shield, the battery and tray, and the alternator just to get my hands down to those plugs. :realmad:

TopDownIfNoFrostBite

9th September 2017, 21:06

Jim Boemler

10th September 2017, 02:37

Chuck H

10th September 2017, 13:30

I thought about taking the wheel off, but had the car up on ramps at that point. And it wasn't high enough to really come in from the bottom. I either need to get some taller ramps, or next time put the back on the ramps and lift the front up higher on jack stands. Plus the long tube header really takes up a lot of room on that side of the engine and makes it hard to get at anything behind it.

Unfortunately, I may have put on a pound or two in the last few years, and I can't squeeze under cars as easily as I used to. :bang:

Only good thing is that I finally notched the two holes on the bottom of the heat shield in the engine compartment so I only have to loosen those two bolts and remove the nut and I can get that sucker in and out. Those two bolts are a nightmare to get to. I was really tempted to just leave that out, but I don't think the "ceramic" coating on my header is all that good, and I didn't want to mess up anything else under there. If I ever replace the header with something else, I'm springing the extra money for SwainTech coating, because I've used that before and I know how well it works. I had to start the car for maybe 30 seconds at one point, and the header was too hot to touch for 10 minutes after that.

Chuck H

11th September 2017, 08:17

Hate to bump my own thread, but I was curious how the ECU reacts when it thinks the front O2 sensor isn't working.

I plan to try some logging tonight to see what my A/F readings and fuel trims are looking like, because I would swear that the car isn't in some limp mode. It's probably running a bit rich, because mileage isn't spectacular and the tailpipes are a bit sooty, but it runs pretty smoothly and makes decent power and it will pull right to the raised redline. So either the limp map is tuned pretty well for performance or it's still getting decent A/F readings from the sensor, even though it fails the heater resistance test. :dunno:

olgzr

11th September 2017, 12:50

Hate to bump my own thread, but I was curious how the ECU reacts when it thinks the front O2 sensor isn't working.

I plan to try some logging tonight to see what my A/F readings and fuel trims are looking like, because I would swear that the car isn't in some limp mode. It's probably running a bit rich, because mileage isn't spectacular and the tailpipes are a bit sooty, but it runs pretty smoothly and makes decent power and it will pull right to the raised redline. So either the limp map is tuned pretty well for performance or it's still getting decent A/F readings from the sensor, even though it fails the heater resistance test. :dunno:

I may be mistaken, but the heater is a separate circuit from the circuit that measures the mixture. The heater can be open and the 02 sensor part still works but the sensor takes longer to get up to its operating temperature. That's why it has 4 wires.

TopDownIfNoFrostBite

11th September 2017, 16:57

Chuck H

13th September 2017, 22:23

I know everyone on here is probably tired of hearing about my trials and tribulations, but I'll update this anyway. :p

Replaced the front O2 sensor tonight with the OEM Denso equivalent and re-installed the GWR extension cable that came with my header, but dressed the extensions a little differently to try to keep them even further from the header primaries. It seems to have been a success -- took a short drive and no codes, even when I checked with my EcuTEK. Before I couldn't even back out of the garage without getting P0130 and P0134. :D

And thanks to TopDown for the suggestion to go through the wheel well. Even with re-dressing the extension cables, it was probably a half hour job that way instead of 3 or 4 hours the hard way I was doing it before. :thumbs:

I bought a new rear sensor as well, and a replacement extension cable from GWR. Just waiting for the extension to come in and I'll replace that one as well, since the plugs are all melted and make intermittent connection, I believe.