Service

Mercedes DPF, AdBlue & EGR Repair in London

We diagnose and fix Mercedes DPF, AdBlue (SCR/NOx) and EGR faults at their root cause — whether that is a blocked DPF, a failed AdBlue injector, a NOx sensor, a split EGR cooler or differential pressure sensor — and clear the associated limp-mode warnings permanently.

DPF, AdBlue & EGR
Price: Diagnostic from £85. Repair quoted after fault confirmed. Typical time: Diagnostic: 1–3 hours. Repair: varies.
Get a fixed-price quote 0333 567 2161

Modern diesel Mercedes engines — OM642, OM651, OM654, OM656 — are clean and efficient, but they rely on three closely linked emissions systems: the DPF, the AdBlue SCR system, and the EGR. Get one wrong and the car goes into limp mode. We work on all three every day.

DPF: cleaning vs replacement

A blocked DPF does not always need replacing. We start with a full diagnostic (soot and ash loading, differential pressure, live regen behaviour) and decide whether an off-car clean, a forced regen, or a replacement is the right answer. Replacing an expensive DPF when the root cause is a failed injector or glow plug wastes your money.

AdBlue / SCR faults

Common AdBlue faults on Mercedes are failed NOx sensors, crystallised AdBlue injectors, blocked lines and failed SCR heaters. We read the SCR control unit, test flow and pressure, and replace only the component that has actually failed.

EGR cooler failures

On OM642 and OM651 engines a leaking EGR cooler is a common cause of coolant loss, white smoke, and repeated overheating warnings. We pressure-test the cooling system and replace the cooler if confirmed.

What's included

  • DPF soot / ash analysis via Xentry live data
  • Forced regeneration
  • DPF off-car cleaning (specialist partner)
  • AdBlue system diagnostics
  • NOx and AdBlue injector replacement
  • EGR valve / cooler replacement
  • Full fault code clearance and limp-mode reset

Common symptoms we see

  • "Engine malfunction" warning
  • "AdBlue: starts not possible in X miles"
  • Limp mode / reduced power
  • Black smoke / white smoke
  • Repeated DPF regen cycles
  • Coolant disappearing with no obvious leak

Frequently asked questions

  • Can a blocked DPF be cleaned instead of replaced?

    In most cases yes. We check soot and ash loading on Xentry first. If ash loading is below the limit, a forced regen or an off-car clean usually restores function. Only when ash loading is beyond the service limit do we replace the DPF.

  • My Mercedes says "AdBlue: starts not possible in 900 miles". Can you fix it?

    Yes. The countdown is triggered by a specific fault in the AdBlue / SCR system — usually a NOx sensor, AdBlue injector or SCR heater. Once the root cause is fixed and verified, we clear the countdown on Xentry.

  • What are the symptoms of a failed Mercedes EGR?

    Rough idle, reduced power, coolant loss (if the EGR cooler is leaking), white smoke, and fault codes relating to EGR valve position or cooler leaks.

Quick quote

Get a quote for dpf, adblue & egr

Tell us the model, the reg and what’s happening — we’ll come back with a fixed price.

Which Mercedes do you drive?

Tell us about your car so we can prepare an accurate quote.

What do you need?

Choose the closest match — we'll discuss the details when we call.

How can we reach you?

We'll call or email within a few hours with a quote. No obligation.

Or call 0333 567 2161

Book your Mercedes in for dpf, adblue & egr

Genuine parts. Dealer-level tooling. 12-month workshop warranty.

Request a quote 0333 567 2161