NOx Sensor Fault Cost: What You Pay to Diagnose and Sort It

Quick answer: The cost of a NOx sensor fault depends on what the diagnosis finds. With us, the mobile diagnostic visit is £185 and it’s included in the price if the full fix goes ahead on the day. If the cause is wiring, a connector or the fluid, a garage can often sort it cheaply. If a sensor really has failed, you have two routes: a replacement through a garage or dealer (we don’t fit sensors, so get a written quote that includes the part, labour and any coding), or, for eligible off-road, export or motorsport vehicles, our software service from £249 with a lifetime warranty. The expensive mistake is paying for a part before anyone has proved it’s the part that failed.

A NOx sensor code usually arrives with a warning light, sometimes an AdBlue countdown, and then a quote. This guide explains what you’re actually paying for at each step, so you can compare options with real readings in front of you. For how the sensors work and why they fail, see NOx sensor faults explained.

What does it cost to diagnose a NOx sensor fault?

Our mobile diagnostic visit is £185. We come to your home, workplace or depot, read the stored codes with their freeze-frame data, and test the system live: both NOx sensor readings with the engine running, the wiring and connectors, dosing pressure, AdBlue quality and the heater. You get written findings and control module resets, and the £185 is included in the price if the full fix goes ahead on the day.

That step matters because a NOx code doesn’t always mean a failed sensor. Codes like P229F and P2201 can be set by wiring, a connector or a fault elsewhere in the system, and P20EE is more often an injector or dosing problem than a sensor.

What if it’s not the sensor?

Then it’s often the cheapest outcome. Damaged wiring, a corroded or loose connector, a blown fuse or stale AdBlue can all set NOx-related faults. We don’t fit parts or do wiring repairs, so if that’s what the readings show, we tell you, and any garage can usually put it right. The written findings tell them exactly where to look.

What does a sensor replacement involve?

If a sensor has genuinely failed, a garage or dealer can replace it. Most vehicles with AdBlue have two NOx sensors, one before and one after the SCR catalyst, so the diagnosis should say which one. When you ask for a replacement quote, check it covers:

• the part itself, and whether it’s genuine or aftermarket;
• fitting labour, including access on your vehicle;
• any coding, adaptation or resets the vehicle needs afterwards;
• whether the price includes the other sensor if it’s likely to follow.

We don’t quote for sensor replacement because we don’t do it. Get the figure in writing from the garage or dealer so you’re comparing like with like.

What does the software route cost?

Our software service, including a NOx sensor delete, starts from £249 for eligible vehicles, with diagnostics included. ECU unlocking, where a vehicle needs it, is quoted separately before any work starts. We save your original ECU file first, and the work carries our lifetime warranty: if the work we carry out ever gives trouble, we put it right at no charge. Our AdBlue delete cost page explains what moves a quote within our range.

Removing or disabling emissions equipment, including the AdBlue/SCR system, is not permitted on vehicles used on public roads and can affect your MOT, insurance and compliance. Deletes are carried out for off-road, motorsport, competition and export vehicles, and we check vehicle and use eligibility before any software work. Read is an AdBlue delete legal in the UK? before deciding.

What are the hidden costs of leaving it?

• A no-start. Many NOx faults start an AdBlue countdown. Once it reaches zero the engine won’t restart, and a recovery truck to a garage costs money and time. Our guide to the no-start countdown explains the timeline.
• Repeat code clears. Paying for a clear that comes back in a day or two, and losing the freeze-frame data that would have found the fault.
• The wrong part. Replacing a sensor when the real cause was the wiring or the injector, and still having the warning afterwards.
• The MOT. A live emissions warning can be an MOT problem, so a fault left until test day can mean a retest.

How do I keep the cost down?

Get a diagnosis before you buy parts, don’t keep clearing codes, and act while there are still miles on any countdown. Send us your registration, the exact dash message and any code you’ve been given, and we’ll tell you what the visit involves before we set off.

Do you come to me?

Yes. We’re mobile across London, Surrey, Sussex and Kent from our base near Gatwick, 8am to 8pm, 7 days a week, and work at homes, workplaces and depots, subject to technician availability. Send your registration and postcode and we’ll confirm whether we can attend and when. The full list of towns is on our areas covered page.

Want it looked at? Get a fixed quote with your registration and the exact dash message. Or call 0207 046 1823 (London and Kent), 01483 963253 (Surrey), 01293 366085 (West Sussex), 01273 950316 (Brighton and East Sussex), or WhatsApp 07403 415966.

NOx sensor fault cost: frequently asked questions

About the author. Written by Mobile AdBlue Fix, a mobile AdBlue, NOx and SCR specialist based near Gatwick and covering London, Surrey, Sussex and Kent. We diagnose with manufacturer-level equipment before recommending anything, check vehicle and use eligibility before any software work, save your original ECU file, and back our work with a lifetime warranty. How our warranty works.