P0031 troubleshooting

Technical Area Engine, Transmission, Exhaust etc
1

[ edit: turned out to be a fault O2 sensor (front) ]

Hi everyone

  1. My model of MX-5 is: MX5 NB-FL
  2. I’m based near: Manchester
  3. I’m looking for technical help or recommendations on:

I have been trying to track down a pesky P0031 code which indicates a short / open circuit at the front O2 sensor.

Having had a peak at the wiring (see attached) I get some strange voltages. I am very very bad at car electrical stuff so any help is greatly appreciated. Annoying the Haynes doesnt have a wiring diagram that I could see.

the blue and white ones seem to be relating to a signal with the black ones being the power for the o2 sensor pre heater?

Tom

mx5 1
mx5 1740×674 68 KB

2

With the the sensor disconnected, check the resistance of it through the black wires (just to confirm, the back wires have silver coloured terminals not gold), you should get between 5.0 and 6.8 ohms. That checks the integrity of the heater element and as a guess is where your problem will lie. You should have a 12 volt feed between one of the black wires and body ground, when connected and with the ignition on.

3

Thanks Rob! Looks like my sensor is a dud. I gave the contacts a clean and I’m getting 12v now for the heater so will get a replacement.

Thanks

EDIT: to confirm it was the old sensor that was a faulty, a £30 ebay replacement has cured the problem