High mileage, slow traffic and tired NOx sensors
A diesel that earns its keep around central Croydon, as a private hire car, a delivery van serving the shops near Surrey Street Market or a trader's pickup, can rack up serious mileage without ever getting far from the Clocktower. Much of it is at walking pace along London Road and Brighton Road, with bus stops, signals and constant stop-start. Short gaps between fares mean the engine is often switched off hot and restarted soon after, which is when deposits tend to form at the dosing injector. That's hard use for an SCR system.
NOx sensors sit in the exhaust stream and run hot, and on high-mileage diesels they're among the more common AdBlue-related failures. A tired sensor can read wrongly rather than fail outright, so the ECU decides the SCR catalyst isn't working and sets an efficiency fault even though the dosing is fine. Swapping parts on a guess gets expensive quickly, which is why we compare live readings from the upstream and downstream sensors before recommending anything. We also check the wiring to each sensor, since connectors near the exhaust can corrode and give readings that look like a sensor failure.
For drivers whose car is their income, the countdown is the real worry. We'll tell you straight how many miles you have and whether it's sensible to keep working until the booking. Once we've confirmed the fault you get a written quote, and simpler jobs such as a sensor or dosing module are often finished within the day if the part is available. Larger jobs, such as a tank module, may need ordering.
From the town centre it's about 4.5 miles to Soho Mills, over the Flyover and along Croydon Road through Waddon and Beddington. Croydon has six camera-enforced Healthy Neighbourhood filters, so stick to the main roads rather than cutting through side streets you don't know. If the countdown has run out, we can arrange collection instead. Repairs come with a 3-month workmanship warranty.