Rear O2 sensor isn't switching — heater or element failure.
P0146 — also written PO146, P 0146, 0146 — is the OBD-II code for o2 sensor circuit no activity (bank 1, sensor 3). Same code, same fix: this page covers every spelling of it.
This code means the very last sensor in your exhaust chain—the one checking the final stage of cleaning—has stopped talking to the ECU. It's extremely common on long-wheelbase Vauxhalls and older Jag saloons with complex emissions setups.
P0146 is a emissions fault code, typically costing £90–£320 to put right in a UK garage.
What P0146 actually feels like to drive
- EML light stays on, even after a reset.
- Passed the MOT emissions test but the light is still staring at you.
- A slight drop in MPG, though not as drastic as a front sensor failure.
- The car feels 'flat' when cruising at 60mph on the A-road.
- Sometimes a faint smell of rotten eggs from the tailpipe if the sensor has failed 'rich'.
What causes P0146?
- Failed sensor heater
- Failed sensor element
- Open circuit heater
UK vehicles that throw P0146 most often
- Vauxhall Insignia 2.0 CDTi (A20DTH) 2008-2015
- Jaguar XF 3.0 V6 Petrol 2008-2012
- Land Rover Discovery 4 5.0 V8 2009-2013
- Range Rover Sport 4.2 Supercharged 2005-2009
- Vauxhall Astra J 1.6 VVT 2009-2015
- Volvo V70 2.5T 2007-2010 (B5254 engine)
How P0146 is fixed
- Replace sensor
The P0146 misdiagnosis that wastes money
I see folk throwing money at new catalytic converters far too often with this code. They assume 'no activity' means the cat isn't working, but P0146 is purely an electrical 'is it alive?' check for the sensor itself. I’ve also seen DIYers replace the pre-cat or the main post-cat sensor by mistake. Bank 1, Sensor 3 is the one furthest down the pipe, often after a secondary cat. Check the loom first; I’ve had many a Land Rover where the wiring has simply melted against the exhaust heat shield before you go buying parts.
What a UK garage should charge for P0146
A decent diagnostic plug-in will run you £50 to £80 at an indie. For the part, don't buy the £20 eBay specials; they last a week. A Bosch or NTK sensor will cost between £70 and £140 depending on the lead length. Factor in an hour of labour (£60–£100) because these rear sensors are usually rusted solid into the pipe and need the oxy-acetylene torch to move. If you go to a main dealer, expect a bill closer to £350 once they've added their 'genuine' part markup.
P0146 repair cost in the UK
Most P0146 repairs land between £90–£320 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 P0146
If you're taking this to a garage, ask them to 'graph the live data' for Sensor 3 while the car is at operating temperature. If the line is a flat 0.45V, the sensor is dead or the wire is snapped. Don't let them just 'clear the code and see'—it'll come back as soon as the drive cycle hits the motorway. Also, insist they check the fuse for the O2 heater circuit; on some Peugeots and Citroens, a blown fuse for something totally different can take out the sensor power, making you think the sensor is a dud when it's just got no juice.
Can you drive with P0146?
Yes.
Urgency: medium.