DPF or AdBlue fault? Tell them apart first.
Two amber lamps sit on the same dashboard, but they belong to two different systems and mean two different jobs. One is a filter that traps soot, and the other is a fluid that treats the exhaust gas. Knowing which you have before you call saves you being quoted for the wrong thing, and this page shows you how to tell.
- Delete on your driveway
- Repair at JF Automotive
- Delete from £245
What each warning looks like
The symbols differ by make, so read the message as well as the picture. Quote it to us as it is written.
DPF: a box with dots and a pipe each end
The filter is loaded, or a regeneration has failed. Steady amber usually means it wants a long drive. Flashing, or with a message, means it has stopped trying on its own. There is no countdown, but limp mode follows if it is ignored.
“Diesel particulate filter: see owner's manual”AdBlue: a canister, a tank, or words
The VW group draw a canister pouring, Mercedes and PSA draw a tank, and many makes just write the words. Very often it comes with a mileage countdown to no-start. The SCR system has logged a fault or believes the tank is low.
“Add AdBlue: no engine start in 600 mi”Or just the engine light
Ford, BMW, Land Rover and others report both systems through the ordinary engine lamp, with the detail in the driver display or not at all. Then the stored code is the only way to tell, so send it to us if you have it.
“Emissions fault: reduced power”What each one is, and what goes wrong
Both sit in the exhaust of a modern diesel and both are watched by the engine ECU. That is where the similarity ends.
The DPF
- A ceramic filter that traps soot, then burns it off when the exhaust is hot enough for long enough
- Blocks when it cannot regenerate: short journeys, a failed sensor, a sticking EGR valve, a glow plug
- Fixed by finding the cause and running a forced regeneration, though ash, unlike soot, needs cleaning or replacement
- Codes: P2002, P2452, P2453, P2463, P242F
Most blocked filters we see are not dead filters. The car has stopped regenerating for a reason, and finding that reason is where JF Automotive start.
DPF delete or fix →AdBlue and SCR
- A urea fluid sprayed into the exhaust to turn nitrogen oxides into nitrogen and water
- Faults when a sensor, heater, pump or injector fails, or the fluid is bad, and a top-up rarely clears it
- Fixed by finding the failed part, and the countdown resets when the fault is repaired, not before
- Codes: P203F, P204F, P207F, P20E8, P20EE, P229F
From the driver's seat every AdBlue fault looks the same. Underneath it is nearly always one of a handful of things, and diagnostics on the ramp tells them apart.
AdBlue delete or fix →They are often faulted together on a car that does short journeys, because neither system gets the heat it needs. A car with both lamps on is not two disasters. It is usually one cause showing up twice.
What is behind almost every AdBlue fault
You see one amber lamp, one message and one countdown. Underneath, it is almost always one of these.
- Crystallised urea - AdBlue crystallises as it dries, around the injector nozzle, in the dosing line and in the tank, and wrecks the fine spray the system depends on. Short journeys, long spells parked and spillage while topping up all make it more likely.
- A failed NOx sensor - there are two of them, one either side of the catalyst, in a hot dirty part of the exhaust. It is one of the commonest failures on the whole system. A dead sensor makes the car believe the SCR is not working when the dosing side is fine.
- A failed AdBlue pump - it has to build and hold pressure for dosing to happen at all. As it weakens the car logs a pressure fault, stops dosing and starts the countdown.
- A failed tank heater - AdBlue freezes at minus 11 C, so the tank and lines are heated. When the heater or its sensor fails the system faults in the cold and seems to clear when it warms up, which is what makes it frustrating to chase.
- A blocked injector - it sprays into the exhaust stream and takes a beating from heat and contamination. Partly blocked, it gives an intermittent fault for weeks before it settles into a permanent one.
- A software fault - not every AdBlue fault is a broken part. Sometimes the control software has latched onto a fault, sometimes it is a known issue the manufacturer has released an update for, and sometimes a single out-of-range reading was never cleared. These are the cheapest to put right and the easiest to miss.
From two lamps to one answer
Tell us what the dash says
Send us the registration, which lamps are on, the message as written, any countdown miles, and any code you have.
We tell you which it is, and what it means
From the message and any code, we tell you whether it is the filter or the fluid. If it sounds like a long drive will clear it, that is what we will say. Then it is your choice: delete or repair.
A price, or a workshop booking
For a delete, one fixed figure from the registration and a booking link for your driveway, sooner if the countdown is low. For a repair, the car goes to JF Automotive in Maidstone, who diagnose it on the ramp and quote it before any work starts.
Deleted on the driveway, or fixed at the workshop
For a delete, we read and keep the original file, write the new one and road test it, about an hour at your home or work. For a repair, JF Automotive read the codes and live data from both systems, find the cause, put it right, regenerate the filter if it needs it, and road test it.
Get my price
Give us the registration, which lamps are on, and where you are. We tell you which system it is and, for a delete, come back with a fixed price and a booking link, usually the same day. For a repair we pass you to JF Automotive.
- From £245, quoted on the car
- Fully insured, at your home or work
- No workshop visit, no courtesy car needed
DPF and AdBlue, the questions we get asked
Both lamps are on. Is that two repairs?
Usually it is one cause. A car that does short journeys starves both systems of heat, so the DPF cannot regenerate and the AdBlue injector crystallises. Fix the cause, regenerate the filter, replace whatever has actually failed on the SCR side, and the two lamps go out together. That is physical work, so it is one visit to JF Automotive rather than two.
Can I just top up the AdBlue?
If the message says the tank is low and there is no fault message, yes, top it up and drive it. If the lamp stays on after a top-up and a drive, the car does not believe the sensor, and that is a fault. The full checklist is on the AdBlue light page.
Can I just drive the DPF clear?
Sometimes, if the lamp is steady and the car is otherwise fine. Try twenty minutes above 2,000 rpm at a steady speed. If it is flashing, the engine light is on too, or the car is in limp mode, it has stopped trying on its own and needs a forced regeneration and the cause finding.
Can either be deleted?
Yes. Both can be switched off in software, on the driveway, from the original file, which we keep. The legal position is set out here, and each service page gives a price for either job.
Backed by JF Automotive
Remaps UK is the mobile arm of JF Automotive, a Maidstone workshop that has been tuning cars for thirty years. The files, the calibration work and the rolling road behind your job are theirs. If a job turns out to need a ramp or a dyno session rather than a driveway, it goes to them, and you are not passed to a stranger.
About JF Automotive →Where to go next
AdBlue delete or fix
The two jobs, the nine faults we find, the price, and the legal position in one place.
Read more → The filterDPF delete or fix
What blocks a filter, what clears it, what a forced regeneration is, and the software option.
Read more → Just the engine lightEngine light on
Steady or flashing, what it usually turns out to be, and what a proper read involves.
Read more →