AdBlue temperature sensor fault.
P2042 — also written P2O42, P 2042, 2042 — is the OBD-II code for reductant temperature sensor (adblue/scr). Same code, same fix: this page covers every spelling of it.
This is the 'brain' of the AdBlue system getting confused about how cold the fluid is. It's a classic headache on modern Euro 6 French cars and Vauxhalls where the sensor decides to pack up just as the warranty ends.
P2042 is a sensors fault code, typically costing £100–£400 to put right in a UK garage.
What P2042 actually feels like to drive
- The dreaded 'No Start in 500 miles' countdown appearing on the dash.
- AdBlue warning light is on, even though the tank has just been topped up.
- Engine stays in 'limp mode' with restricted power on the motorway.
- Warning light disappears on a dry day but comes back as soon as it rains.
- The car smells slightly of ammonia near the rear wheel arch.
What causes P2042?
- Sensor failure
- Wiring
UK vehicles that throw P2042 most often
- Peugeot 3008/5008 1.6 & 2.0 BlueHDi (2015-2020)
- Citroen Berlingo/C4 Picasso 1.6 BlueHDi (DV6FC)
- Vauxhall Insignia B 2.0 CDTi (2017-2022)
- Mercedes-Benz Sprinter 2.1 CDI (W906/W907)
- Ford Transit Custom 2.0 EcoBlue (2016 onwards)
- Audi A4/A6 2.0 TDI (Ultra models) 2014-2018
How P2042 is fixed
- Sensor replacement
The P2042 misdiagnosis that wastes money
I’ve lost count of how many times I’ve seen people chuck a brand new £300 AdBlue pump at a car for this code, only to find the light stays on. On most Euro 6 diesels, the temperature sensor is integrated into the delivery unit or the tank itself. In our shop, we often find it’s not the sensor at all, but the 'green crusties'—urea crystal build-up in the multi-plug or a broken wire just behind the rear axle where the harness gets battered by road salt and spray. Look for the simple stuff before replacing the expensive plastics.
What a UK garage should charge for P2042
A basic diagnostic scan is usually £50–£80 at an indie, while a main dealer will sting you for £120 plus VAT just to plug it in. If it’s just a wiring repair, you’re looking at £100-£150. However, if the sensor is baked into the tank (common on PSA vans), a genuine replacement can be £600-£900. Aftermarket repair kits from brands like Bosch or HIDRIA are around £250-£350, plus 2-3 hours of labour. Expect to pay at least 30% more at a main dealer for the exact same plastic bit.
P2042 repair cost in the UK
Most P2042 repairs land between £100–£400 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 P2042
If your garage says you need a whole new AdBlue tank because 'the sensor isn't sold separately,' they aren't necessarily lying, but they aren't trying hard enough either. On many Peugeots and Citroens, you can actually get aftermarket repair kits or use a specialist like 'ACtronics' to fix the board. Insist on a 'continuity test under load' on the wiring harness before they order the tank. If they just clear the code and it comes back in two days, you’ve been fobbed off. Also, ask if they can recalibrate the 'denox' system after the fix, or you'll still be stuck in a countdown clock.
Can you drive with P2042?
Drivable but countdown may start.
Urgency: medium.