Long days at 20mph and what they do to SCR
Walk down a street in the Totterdown Fields estate or Summerstown and many of the cars squeezed in on both sides are small petrol hatchbacks, which don't use AdBlue at all. The diesels that do are mainly the vans delivering along the A24 and the private hire estates working between Tooting Broadway station and St George's. They cover a lot of miles, but much of it is at 20mph, with the engine idling at the Broadway junction. Hospital staff commuting by car add a few more to the mix.
That kind of mileage is hard on the SCR system in two ways. The exhaust spends long periods below the temperature at which dosing works best, so urea deposits build up around the injector. And high total mileage takes its toll on NOx sensors, which sit in the hot exhaust stream and eventually start reading wrongly. Both lead to the same warning on the dash, so guessing between them is a quick way to waste money.
We read the SCR data rather than guess: dosing quantities, NOx readings before and after the catalyst, and how the system behaves once the exhaust is properly hot. Vans usually carry larger AdBlue tanks and some have more complex dosing layouts, but the diagnostic approach is the same. Once the cause is confirmed, you get a written quote, and we'll be straight with you about how long the vehicle will be off the road. For private hire drivers we can often book an early diagnosis, so you know where you stand before the day gets going.
The drive is about 5 miles: Mitcham Road east from Tooting Broadway, through Mitcham to the Cricket Green, then Cranmer Road and Carshalton Road south to Hackbridge. If you're coming from the Trinity Road side, head down to Tooting Broadway first. On narrow terraced streets a van that won't restart is hard to deal with, so tell us if recovery is needed. Repairs carry a 3-month workmanship warranty.