Hello FOC,

I have a 2005 (55reg) focus hatchback climate.

about a month ago my eml light came on and popped up with P0420 on little code scanner.

As i didnt know the exact fault i guessed it was the rear lamda sensors.

My specific exhaust is a maniverter with twin cats / 4 lambda sensors usually found on the c-max.

I bought 2 new sensors from ebay for £20 hoping for a cheap fix, fitted them and needless to say it didnt fix the fault.

The eml light stayed on and the p0420 code remained after trying to turn the light off with my scanner.

I realised that the cat must be at fault so managed to get a replacment cat plus 4 sensors second hand..turned out my cat was indeed dead inside, chunks missing.

i fitted the cat and bingo the P0420 code had gone..only to be replaced with P0156 ( 02 sensor curcuit bank 2 sensor 2)

i thought that it might have a faulty sensor beoing 2nd hand, so i swapped one of my £20 ebay ones for it..

reset the eml and it was off for a day..then back on..swapped it for the other £20 eaby sensor..truned the light off and then it came back on after a day...

i bought a genuine lambda sensor for £100 thinking that the ebay ones were cheap crap..fitted it and the light stayed off for a week..then it came back on..i turned it off..5 days later its back on with the same code P0156..it doesnt do it on start up, usually as im driving.

i doubt 4 sensors are at fault, could this be wiring or ecu fault, the car drives fine and ive not noticed a massive mpg change..the only issues i have noticed is my dials flicker when i start the car at times,and i get a kind of popping through the speakers when i start the car even though the radio is turned down,and the engine sounds like its slightly not turning over as fast as usual on crank up...do i get a battery for it or at the least check running amps/voltage?

i have my mot in around a month and i would lilke to fix this prior.

Any help or advice would be helpfull and very very welcome.

Alex

sounds more likely to be the wiring than the sensor directly to me.....

so you have narrowed it down to a particular sensor have you?

yes i have found the sensor in question,

am i right in thinking the EML light wont fail the mot test, but obv if the emissions are out then that will.

ive checked the 4 wire on the sensor, the 2 heater wires are fine, plus its not giving a p0152 heater code.

The grey wire is giving me an earth, but i am unsure how / what to test on the signal wire..

i can strip/open the loom back to the ecu next to the battery but im just unsure what to check for...

volts? resistance etc?

Alex

im unsure about your problem but i can say that the eml light ON will fail the MOT, as my father in law's did, a few weeks ago.....

Any warning light ont he dashboard will fail an MOT, Basically you should find an earth point on the wire and a live point and just run the multimeter over it for resistance. You would need to check at different points along the wire to see where any damage may be.

A small update,

the p0156 code is still present.. the eml comes on for around a day maybe 2 then goes off for a few days., then comes back on for a couple of days.

Its seems it isnt the sensor, which leaves me to belive its the signal wire of the ecu.

I wil start by taking the engin eloom out and testing the wires..although im not sure how the ecu comes off from the side of the battery casing.

I am also hearing mixed opinions on the EML light being an mot failure.?

A very frustrated Alex

I have never seen a focus with twin cats or 4 lambda sensors?..

The EML light will fail the mot if illuminated. You can get away with other warning lights still as far as I'm aware, for example the battery light.

Did you ever sort this? I have the same problem & I also have the twin cat with 4 sensors. Bank 2 sensor 2 fault.