E250 CDI limp mode problem

[gunning]

Hi guys,

Looking for some advice please....

I have an E250 CDI B/E

It’s throwing up the following fault codes:
P246397 unknown fault
P008700 fuel pressure too low
P025284 particulate filter differential
P245328 pressure sensor bank 1 offset outside tolerance

Are these related or separate reasons for it going into limp mode. Sometimes it drives really well? Most of the time it’s in limp mode.

Before I take it to an MB specialist just wanted to know what the issues were with it.

Any help would be much appreciated

 

[OneForTheRoad]

Alot of error codes are daisey chains from just 1 fault. Yours points to a dpf fault.

 

[jon1971]

Hi guys,

Looking for some advice please....

I have an E250 CDI B/E

It’s throwing up the following fault codes:
P246397 unknown fault
P008700 fuel pressure too low
P025284 particulate filter differential
P245328 pressure sensor bank 1 offset outside tolerance

Are these related or separate reasons for it going into limp mode. Sometimes it drives really well? Most of the time it’s in limp mode.

Before I take it to an MB specialist just wanted to know what the issues were with it.

Any help would be much appreciated

dpf blockage

 

[gunning]

Thanks guys, gone into TMS MB specialist in Truro now. I’ll await his report

 

[400ixl]

It actually points to a sensor fault, not a DPF fault. Probably 2 sensors as there is a tolerance difference between them. DPF issue is a knock on from this stopping the DPF regen activating.

 

[jon1971]

It actually points to a sensor fault, not a DPF fault. Probably 2 sensors as there is a tolerance difference between them. DPF issue is a knock on from this stopping the DPF regen activating.

Its more likely a emission fault that has caused the dpf to block, so sensor flag fault, sensors very rarely fault and 9 out of 10 times a new sensor will flag same fault a few cycles later, if it turns out to be dpf blocked make sure you clean the lamba sensor properly as these get so blocked they cant read and will keep it in regeneration. they only use one for dpf monitor its just a temp sensor.

 

[jon1971]

It actually points to a sensor fault, not a DPF fault. Probably 2 sensors as there is a tolerance difference between them. DPF issue is a knock on from this stopping the DPF regen activating.

Its more likely a emission fault that has caused the dpf to block, so sensor flag fault, sensors very rarely fault and 9 out of 10 times a new sensor will flag same fault a few cycles later, if it turns out to be dpf blocked make sure you clean the lamba sensor properly as these get so blocked they cant read and will keep it in regeneration. they only use one for dpf monitor its just a temp sensor. if your car is maintained properly there is no need for regeneration our merc hit 129k before it did its first regeneration.

It actually points to a sensor fault, not a DPF fault. Probably 2 sensors as there is a tolerance difference between them. DPF issue is a knock on from this stopping the DPF regen activating.

 

[400ixl]

Are you confusing a DPF and a catalytic converter here? The Lamda (O2) sensors control the air to fuel ratio by reading the levels either side of the catalytic convertor, not the DPF. Although they are part of the overall system and if they fail (which does happen far more than the clog) it will cause a fault code and stop a regen happening.

Diesels regenerate every 300 miles or so provided the car is driven appropriately (As in journeys long enough to get the exhaust up to temperature to allow the process to start). Its part of the cycle that happens to stop the DFP filling with soot.

If the regen does not happen then the DPF will fill with soot which will block it. Other than not doing journeys that allow the regen to happen, one of the main reasons is that a sensor fails which triggers a fault code and that stops the ECU starting the regen. Over time these missing regens mean the DPF fails and the car goes into limp mode. Typical sensors that fail are the turbo temp, exhaust temp, Exhaust pressure, DPF and O2 sensors. You do also have to consider the EGR valve and the MAF sensor as well, but they are less likely to give this fault.