Limp home and dpf regen

[galloot633]

Twice my cv90 has been in the garage for work that triggered limp home mode , and both times I was told the dpf needed a forced Regen after the work had been done , is this always the case after running for approx 100 miles in limp mode
Dave

[terp70]

Hi, somehow the engine is generating to much smoke (and cached by the DPF). Cloud be a faulty Oxygen sensor (too rich mixture fuel air) or defect injector. In some cases the engine is burning oil due to leak, causes the engine to smoke (but don't see because DPF takes it out). Look at the Oxygen sensor, is it full of carbon or oily? Any error messages prior to the DPF full message?

terp70

[galloot633]

The car runs fine between those two faults ( egr problem and blown turbo hose ) I'm curious as to how long you can drive in limp mode before the dpf requires a forced regen
Dave

[skyship007]

Originally Posted by galloot633

Twice my cv90 has been in the garage for work that triggered limp home mode , and both times I was told the dpf needed a forced Regen after the work had been done , is this always the case after running for approx 100 miles in limp mode
Dave

You need to get the hidden fault codes read to see what is listed. No need to get a forced Regen unless you get an associated DPF warning light.
There are quite a number of causes for limp mode other than the DPF. A dirty or broken MAF sensor is a popular one and they can sometimes be cleaned up with a spray (MAF cleaner or very good quality contact cleaner).

Limp mode does result in a richer mixture, so driving too far can result in a DPF getting rather dirty, particularly if it was close to needing a normal Regen or nearly blocked with Zinc ash.

[terp70]

Its chicken-egg, limp-mode can be caused by blocked DPF or DPF can be blocked because of driving to long in limp-mode. If you keep on pushing acceleration and car will not accelerate further, air-fuel gets richer and can cause DPF to be more block resulting in limp-mode. Its needed to get to the root cause of the problem. Rich air-fuel can be caused by a lot of different things. Normal if DPF is full, driving 20-30min at 2000-2500 rpm will clean it. If not there is something wrong deeper in the system. Try to make VIDA readout. Simple ODB2 tools do not always get deeper faults in a Volvo.

[galloot633]

That's what I thought , once the fault was repaired the dpf would self generate , but the garage said the car wouldn't get out of limp home until a forced Regen , a sort of catch 22 scenario
Dave