Should limp mode for a blocked DPF reset itself after a long run given the restricted engine performance?

[andyandjulie]

Hi All

Me again.

Recently I had the DPF warning light coming on and I tried to clear it with a good hard long run. This did not work and the car went into limp mode (restricted power and a 2.5K rev limit). I added a decent brand of in-tank DPF cleaner in a good concentration and went for another very long run (albeit with a rev limit). This also did not seem to work but on the advice of a trusted local expert, I scanned for DTCs and reset the blocked DPF code. The car is fine now and the DPF DTC code and problem has not returned.

I would have thought that the car should have put itself right after the second long run with the in-tank DPF cleaner added because it seems to have regenerated the DPF, but it did not reset the DTC fault code. I'm aware of the theory that it takes 3 normal warm up cycles to reset certain faults but the car had had this too. The blocked DPF DTC did not disappear untill I used my diagnostic tool to clear the DTC for the blocked DPF and it's been fine since.

Please let me know what you think guys..

Regards

Andy

[mickthemaverick]

That sounds like a normal sequence to me. Once the ECU has stored a DTC it generally needs a diagnostic tool to clear it.

[Paul-R]

How many miles has the vehicle done?

[Sloppysod]

How long have you had the car, do you know its service history as it's very possible the Eloy tank is low or empty, that's why it worked when you added the fluid to the fuel tank.
I forced the regen cycle on my old C5 by driving at about 50mph with the revs above 2500rpm for a 10 mile, you need to get the exhaust hot.

[andyandjulie]

That sounds like a normal sequence to me. Once the ECU has stored a DTC it generally needs a diagnostic tool to clear it.

Hi Mick

Yes that's what I thought, but a garage told me it should reset after 3 full warm ups. I didn't think it was right either. So the car should have regenerated naturally/passively? when I did the first fast trip? That was my thinking. I'm wondering if what Sloppysod has said further down has any bearing, although my diagnostic tool says there's plenty of EOLYS fluid. I'm thinking I'll be using DPF cleaning additive more often.

Thanks

[andyandjulie]

How many miles has the vehicle done?

Hi Paul

36K now, and it does get a bit of motorway driving (25 mins) every week day.

Thanks

[andyandjulie]

How long have you had the car, do you know its service history as it's very possible the Eloy tank is low or empty, that's why it worked when you added the fluid to the fuel tank.
I forced the regen cycle on my old C5 by driving at about 50mph with the revs above 2500rpm for a 10 mile, you need to get the exhaust hot.

Hi Stu

18 months ish. The service history is decent, it only had 12K on it when I bought it and I've done servicing ever since as per DS schedule. I understand what you say about the EOLYS fluid but the scan tool says I've got quite a bit left.

I'd love to know how you can tell if the car is regenerating. I've tried the LED on the door mirror trick which was suggested by Tricoloured on this forum (brilliant idea) but it has never lit up. I wish DS made it easier to check.

Thanks

[RichardW]

DPF blockage is never really the problem - it's almost always a symptom of something else. It needs a decent scanner that can see the live data to try and figure out what is going on. If it's very blocked for some reason then it won't try and regen it, as to do so might melt / set fire to it.

[tricoloured]

Hi Andy

Does the LED you've fitted light up when you turn on the heated door mirrors ?

It should do.

Bobby

[andyandjulie]

Hi Bobby

Yes it does, thanks for the tip too.

Andy