DPF problems are something we see regularly on diesel Land Rovers at Hunter Cuthill, but one recent Discovery Sport was a good example of why simply carrying out another regeneration isn’t always the right answer.
The vehicle had returned with EGR insufficient-flow and DPF-related concerns. The obvious temptation with a blocked diesel particulate filter is to regenerate it, clear the faults and send the vehicle on its way.
Sometimes that works.
Sometimes it only treats the symptom.
What we found
We began by checking the EGR pressure pipes to make sure they were actually flowing and giving us reliable information. At the time of testing, the pressure pipes checked out correctly.
We then removed and inspected the EGR cooler filter.
It was heavily restricted with soot, despite having been replaced only a relatively short time earlier.
That immediately raised another question: why was it blocking again so quickly?
Further investigation showed excessive soot travelling downstream through the exhaust system. The customer advised us that the DPF had previously been replaced elsewhere approximately 12 months earlier.
Its external condition, however, gave us reason to investigate further rather than simply assuming the DPF was doing its job correctly.
DPF faults usually have a cause
A DPF is designed to catch soot and periodically burn that soot away during regeneration.
If something upstream is causing excessive soot production, or the DPF itself is damaged or no longer functioning correctly, repeated regenerations won’t solve the underlying problem.
Common contributors can include:
- EGR system faults
- EGR cooler restrictions
- Boost or intake leaks
- Incorrect air-flow readings
- Thermostat or operating-temperature problems
- Injector or combustion problems
- Faulty pressure sensing
- Driving conditions that prevent regeneration
- A DPF that is damaged, overloaded or no longer performing correctly
This is why we look at the whole system rather than a single fault code.
A regeneration can still be a useful diagnostic step
There are situations where an on-car regeneration is absolutely worth trying.
We regularly use DPF pressure readings, calculated soot loading, temperatures and live engine data to decide whether regeneration is sensible and safe.
But if a vehicle repeatedly returns with the same problem, it is time to stop resetting the symptom and find out why it keeps happening.
At Hunter Cuthill in Geelong West, we diagnose and repair DPF, EGR, AdBlue and diesel-emissions faults across Land Rover, Range Rover, BMW, MINI and Jaguar vehicles.
Sometimes the cheapest repair is a regeneration.
Sometimes the cheapest repair in the long run is finding out why it needed one in the first place.