P0141 is a heater fault in the rear oxygen sensor, the one behind the catalytic converter. Unlike the front sensor, this one does not control fuelling, so it affects what the car can monitor rather than how it drives. Diagnose soon and drive gently. Indicative UK repair cost is £60 to £300.
That difference is the whole character of this code. The front sensor is part of the control loop: the engine fuels from it. The rear sensor is a referee. Its only job is to watch what comes out of the converter and compare it with what went in, which is how the car decides whether the converter is still working. So when its heater fails, nothing about the way the engine runs changes at all. What changes is that the car can no longer run its catalyst check properly.
There is a consequence of that worth knowing before you spend anything, because it catches people out: fixing P0141 occasionally reveals a catalyst fault that was hiding behind it. With the rear sensor's heater dead, the monitor that would have flagged a tired converter may never have been able to complete. Replace the sensor, let the car run its checks, and P0420 can appear a few days later. That is not the new sensor causing a problem. It is the car finally able to tell you something it had been unable to test.
Can I drive with P0141?
Diagnose soon, drive gently. Of the oxygen sensor codes this is the least urgent in terms of how the car behaves. There is no economy penalty worth measuring, no driveability complaint, and nothing wearing out faster because of it. The two reasons to deal with it are the MOT and the point above: a car that cannot complete its emissions self-checks is a car keeping information from you.
What P0141 means for your MOT
The lamp, and realistically the lamp alone. It is a major defect under section 8.2.1.2 of the DVSA MOT inspection manual for petrol cars first used on or after 1 July 2003, and the sensor is a named component under 8.2.1.1 where emissions equipment that is missing, obviously modified or obviously defective fails on any vehicle first used on or after 1 September 2002.
The measured gases are a different story from the front sensor's heater fault. Because this sensor plays no part in deciding how much fuel the engine gets, a dead heater here has no path at all to the carbon monoxide, hydrocarbon or lambda figures the tester records. Those will read exactly as they would have done with a perfect sensor fitted. So this is a code where the honest answer is that your car will fail on the light while producing clean numbers, and nothing about the gas test tells you anything useful.
What usually causes it
- A failed heater in the rear sensor. The usual outcome. The rear sensor sits further down the exhaust where it is colder and wetter, and it is exposed to more road salt and spray than the front one, which is why these often fail before their front counterparts despite doing less work.
- A fuse or supply fault. Where the heater circuits for both sensors share a supply, one failure takes out both. If the front sensor's heater code is stored as well, that shared supply is the first thing to look at rather than the last.
- Wiring damage underneath the car. This sensor's lead runs along the underside, which means stone chips, corrosion at the connector, and in a lot of cases a lead that has been crushed by a jack or caught on a ramp.
What it costs to fix in the UK
£60 to £300. A sensor is the bulk of it, and fitting is usually straightforward because the rear sensor is generally reachable from under the car. The top of the range is where it has rusted into place, which under a British car with a few winters behind it is more likely here than at the front, and where the fitting becomes a penetrating-oil-and-patience job.
Factor in the possibility described above: if a converter fault emerges once the sensor works again, the bill does not stop at the sensor. Reading what a car diagnostic costs in the UK alongside that is worth doing before you commit.
These are indicative UK ranges for guidance only. Actual causes and prices vary by vehicle, and a stored code points to a system, not always the exact part.
What to check first
- Look at whether the front sensor's heater has flagged too. Two heater codes together point at something they share, and one on its own points at the sensor named in it. That is thirty seconds of reading that decides the whole approach.
- Get under the car and follow the lead. This is the sensor where physical damage genuinely competes with electrical failure. Look for a crushed or stretched lead, a connector full of water, and corrosion where the lead is clipped to the underbody.
- Test the heater circuit at the sensor plug. Resistance across the heater pins and supply voltage at the feed, which between them separate a dead element from a circuit that is not being fed.
- Plan for the catalyst monitor to run afterwards. Once the sensor is working, drive the car normally for a few days and read it again rather than assuming the job is closed. If a converter code appears, you have learned something real, not caused something new.
Related codes
- P0135, oxygen sensor heater circuit (Bank 1 Sensor 1). The same fault on the front sensor, where the consequences are quite different, and the page with the shared-fuse test set out in full.
- P0420, catalyst efficiency below threshold. The code that can surface once this sensor is working again, and the reason not to treat the sensor as the end of the story.
- P0133, oxygen sensor slow response (Bank 1 Sensor 1). Useful for understanding the difference between a sensor that controls fuelling and one that only observes.
Get it narrowed down before you spend
A stored code tells you which system is unhappy, not which part has failed. If you want it narrowed down before you spend anything, send the code and your symptoms and a mechanic will read them personally. Quick Diagnosis is £20, and if we can't help, you don't pay.
Written by the First Diagnostic mechanic. Over a decade in the trade: a VW-only workshop running diagnostics and electrical repair, then BMW-only through to full engine rebuilds. Now an independent all-makes workshop, plus building and wiring drift cars for competition, including trackside work as head mechanic. More about who reads your codes.