# NOx sensor fault | what to do now > NOx sensor fault: Component risk. A NOx sensor fault is the most common collateral failure after AdBlue contamination —… - URL: https://adblueinfuel.co.uk/nox-sensor-fault/ - Focus: nox sensor fault - Updated: 2026-09-22 - Phone: 01295 380724 (From just £89 call-out fee) - Publisher: AdBlue in Fuel — a service by Forecourt Assist — Forecourt Assist is a trading name of Fuel Fixer Ltd, company no 08520551, registered at Fairway House, Portland Road, East Grinstead, RH19 4ET, a company of Fuel Fixer International. --- ## NOx sensor fault Short answerA NOx sensor fault is the most common collateral failure after AdBlue contamination — and also the most common cause of an SCR fault with no contamination at all. Get it confirmed before buying one. Call 01295 380724. Most SCR systems run two NOx sensors, one upstream and one downstream of the catalyst, and the difference between them is how the vehicle proves conversion is working. They sit in a hot, corrosive exhaust stream and they are a known wear item. They are also what fails after contaminated fluid has been dosed. Crucially, a genuine conversion failure and a failed downstream sensor produce a very similar fault, and only live data separates them — which is why sensors get replaced unnecessarily so often. Call 01295 380724 From just £89 call-out fee ## NOx sensor fault — the severity verdict **Key facts** | Severity | Component risk Frequently needs SCR component work rather than a drain. Quoted before a technician travels. | What went where | NOx sensor fault | Direction | SCR system fault | Typical cost | £160–£600 typical total, from a £89 call-out | Time on site | About 75 minutes | Call-out | From just £89 call-out fee | Helpline | 01295 380724, 24 hours £89 is the call-out. An AdBlue tank drain and flush is quoted on the phone before a technician travels. If the SCR system needs component replacement — dosing injector, pump, tank or catalyst — that is separate, and you will be told before any work starts. If this is a job we cannot fix at the roadside, we will tell you that on the phone rather than after we arrive. ## What to do right now - Get live data read before ordering a sensor — they are not cheap and they are frequently replaced in error. - Note whether the fault appeared after a contamination event or on its own. - Call 01295 380724. ## What a technician actually does Live upstream and downstream NOx values compared against expected conversion, the wiring and connector checked, the specific sensor confirmed, and replacement quoted before it is fitted. ## Why this is not the same job as the other direction This is an SCR system fault rather than a wrong fill, so the first job is reading the codes rather than guessing at a part. The same dashboard message covers a bottle of fluid and a catalyst. ## Common questions ### Can I drive with a NOx sensor fault? Often yes for a short period, but a fault that the system reads as failed conversion leads into the inducement sequence, so it is not something to leave. ### Why do NOx sensors fail so often? They live in hot, corrosive exhaust gas and they are a wear item. Contaminated AdBlue dosed into the exhaust accelerates it considerably. ### Is the sensor or the catalyst at fault? That is exactly what the live data answers, and exactly why a sensor should not be bought on the strength of a code alone. ## What customers say 4.8 out of 5 from 2,190 Trustpilot reviews. What reviewers mention most is that the technician stayed calm and professional with a driver who was embarrassed and stressed, and that somebody arrived when they said they would. The most common criticism is price. People do not expect a wrong-fluid job to cost what it costs, and that is a fair complaint to publish rather than bury. The answer is the From just £89 call-out fee, a quote given on the phone before a technician travels, and being told when a job cannot be done at the roadside rather than after somebody has arrived and charged for the visit. ### Related AdBlue problems AdBlue warning lightAdBlue countdown and no restartAdBlue limp modeAdBlue system faultAdBlue crystallisationAdBlue tank drainAdBlue system flushBlocked AdBlue injectorAdBlue pump failureFrozen AdBlue ### Start from a symptom instead AdBlue warning light is onA countdown to no restart is showingThe engine will not restartPower loss or limp modeWhite crystal deposits on or under the vehicleThe AdBlue gauge reads wrong ### By vehicle class CarsVansPickupsHGVsBuses and coachesMotorhomesAgricultural and plant ### Where we cover NOx sensor fault in BasingstokeNOx sensor fault in BuckleyNOx sensor fault in Conwy ## Who you are dealing with AdBlue in Fuel is a service by Forecourt Assist. Forecourt Assist is a trading name of Fuel Fixer Ltd, company no 08520551, registered at Fairway House, Portland Road, East Grinstead, RH19 4ET, a company of Fuel Fixer International. Fuel Fixer International is owned by Stockbridge Capital Holdings. Reference: Urea (Wikipedia). ## Across the Fuel Fixer network Diesel in PetrolFuel Doctor FleetFuel Fixer IrelandMisfuel DoctorEvery brand above belongs to Fuel Fixer International, owned by Stockbridge Capital Holdings. The directory lives on the operator's own site: forecourtassist.co.uk/network.