Downstream sensor flat-line signal.
P0140 — also written PO14O, P 0140, 0140 — is the OBD-II code for o2 sensor no activity (bank 1 sensor 2). Same code, same fix: this page covers every spelling of it.
This is your post-cat sensor (the 'policeman') going flat-line, usually because the sensor's dead or the wiring's been chewed by the elements. It's a classic MOT fail on many common UK hatchbacks like the Corsa or Fiesta.
P0140 is a sensors fault code, typically costing £100–£300 to put right in a UK garage.
What P0140 actually feels like to drive
- The EML (Engine Management Light) is staring you in the face on the dash.
- Absolutely no change in how the car drives—it's usually perfectly smooth.
- A slight increase in fuel consumption as the ECU falls back to 'safe' maps.
- Failures on the MOT 'Major' defect list for having an active EML.
- The light might go out for a day after a long run, then pops back on during a cold start.
What causes P0140?
- Failed sensor
- Wiring fault
UK vehicles that throw P0140 most often
- Vauxhall Corsa D/E 1.2 & 1.4 (A12XER/A14XER) 2010-2019
- Ford Fiesta 1.25 Zetec (Sigma) 2008-2017
- Volkswagen Golf MK6 1.4 TSI 2008-2013
- Mini Cooper R56 (N12/N16 engines) 2006-2013
- Nissan Qashqai 1.6 Petrol (HR16DE) 2007-2013
- Peugeot 208 1.2 PureTech 2012-2018
How P0140 is fixed
- Sensor replacement
The P0140 misdiagnosis that wastes money
I’ve lost count of how many times I’ve seen brand-new cats fitted because a 'mate with a scanner' saw this P0140 code and assumed the catalytic converter was dead. It’s total madness. You get guys spending £400 on a cheap, nasty aftermarket cat that’ll never pass an MOT on emissions, when the real culprit is a £60 sensor or a broken wire near the heat shield. It's almost always the sensor's internal heating element or the signal line failing, not the cat itself. Don't throw the baby out with the bathwater.
What a UK garage should charge for P0140
You’re looking at about £50 to £80 for a decent diagnostic plug-in to confirm it’s the sensor and not the loom. A quality Bosch or NTK replacement sensor usually runs between £70 and £130 from a motor factor like Euro Car Parts or GSF. Labour is usually an hour—around £60 to £90 depending on if the old one is seized. If you go to a main dealer, expect to pay £300+ because they’ll charge £150 an hour and mark up the part by 100%. All in at an indie, it’s a £180-£220 job most days.
P0140 repair cost in the UK
Most P0140 repairs land between £100–£300 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P0140
If you're taking this to a garage, ask them to 'back-probe the signal wire with an oscilloscope or a high-end live data tool' rather than just reading the code. If they just say 'it needs a sensor' without looking at the wiring, walk away. On these modern VAG or Ford engines, the loom can rub through against the subframe. Also, insist on a Bosch, Denso, or NTK sensor. I refuse to fit those 'universal' £20 jobs from eBay—they have the wrong resistance and you’ll be back in my workshop with the same light on within a fortnight.
Can you drive with P0140?
Drivable.
Urgency: low.