DPF light still coming up after two cleans?

[Sophieeleanorx]

I have a Peugeot 308 14 plate, it was going into limp mode so had the dpf cleaned and it was ok for a few days the back into limp mode again. Took it back for another clean mechanic said it was clean nothing coming out of it on the last flush. 2 weeks later it’s back again.
Not sure whether to take it to Peugeot now and get charged an arm and a leg or whether to take it back to my usual mechanic and have a new dpf. Could it be anything else?

Thanks in advance

[0ddball]

There is usually a pressure sensor which measures the pressure before and after the dpf. The difference in pressure is used to calculate how blocked/full it is. If either of the pipes to the sensor, the sensor itself, or the wiring to it are damaged, the ECU will get a false reading.

You really need to know what error code is causing the limp mode.

[Otispunkmeyer]

0ddball said:

There is usually a pressure sensor which measures the pressure before and after the dpf. The difference in pressure is used to calculate how blocked/full it is. If either of the pipes to the sensor, the sensor itself, or the wiring to it are damaged, the ECU will get a false reading.

You really need to know what error code is causing the limp mode.

That depends

I know of some OEMs where there are 2 calculations. Open and Closed loop. The closed loop one uses the sensor for dP reading, but only at higher speed/higher loads. At lower speed/load (like urban driving) they use a open loop method which is basically a best guess based on fuel and air used. Its a model.

It is possible for the two to go out of sync. After manual cleaning you should reset the DPF parameters in the ECU (ie reset that open loop model and any regen flags). There are tools that do this, but in my experience, it doesn't always work. I've force regenerated DPFs before and then had the car perform a regeneration again on the very next drive because the diagnostic tool couldn't reset the DPF information (even though it said it had).

How has he been cleaning the DPF?

[Automaton]

Because it's an emissions fault the code will be readable with any half decent ebay obd2 code reader and a free app like torque lite.
If its the modeled/simulated reading causing a fault then a long motorway drive of an hour plus should reset it but obviously that's not a great idea if it's in limp mode.
It could be the delta pressure sensor or it could be something like a collapsed filter or holed filter or an obstruction or leak elsewhere in the exhaust could potentially throw it out.
Could also maybe be an exhaust temperature sensor.
I found this with a quick Google.. https://www.google.com/url?sa=t&source=web&amp...

Edited by Automaton on Monday 2nd November 11:13