508 1.6 e-hdi intermittent limp mode

[DimitarK]

Hi all.
I recently got a 508 1.6 ehdi from 2011, aka one of the first generation with all their quirks ..
The car is the robotic gearbox which i believe has nothing to do with the problem that it experiences ..

When driving on the highway the car randomly goes into limp mode without any particular reason ... sometimes it need about 15 kilometers with 110-130 km/h .. some times it takes 150 kilometers to get a limp mode ...

It does not spit any errors on the dash, or on a regular elm bluetooth while the car is in limp mode.
Right after shutting off and starting again - the car drives absolutely fine until it does the same ... it has done it only on highway so far at least 5-6 times for the last 3 weeks.

My lexia was not working so i had sent the car to a local workshop who found a stored error for overboost.
- P2563 (Boost pressure magnet valve too high)
- P1496 (Boost pressure too high)
- P11AA (Boost pressure over max value)
They did change the magnetic valve for the turbo vanes and have tested vacuum supply. Tested the car and got it back to me ..

And so this weeked had a first longer drive on the highway - Kaboom - the same situation out of nowhere ... happened only once though .. after shut down this time the car had trouble starting ... starts almost like one of the injectors is not really working ... even died ... but after about 10 seconds of the car coughing and running rough - it went fine ... and was able to drive 60km more on the highway without any errors ...
Back home i got my lexia to start up and after diagnostics it did not show any errors .. like nothing ..

Not to mention that for some reason the version of lexia (diagbox) that i got is somehow not showing me any menu with stored errors that have appeared back in the time ..


So the question is - does anybody have an idea what to start suspecting? Also how can i access errors stored from diagbox ...? I really would like to see what was the cars reason for going into limp mode ..

[PaulC5]

Maybe the latest problem is different, possibly a fuel one. Has the fuel filter been changed recently or if not is it due ?

[DimitarK]

The fuel filter has been changed 3000kms ago together will oil service and air filters …
Its an interesting problem that i frankly am a bit puzzled over ..
I even considered the mechanism of the turbo vanes that may be failing or something of that sorts..?

[DimitarK]

Ok seems like i got my diagbox back up and running … the error still comes every now and then, sometimes after driving 300kms, sometimes after driving 2 kilometers (right after it had shiwn up again) and only on highway speeds..

Started suspecting dpf regen problem so i check when was the last time it was regeneated and that seems very puzzling - 4000kms …
My prrvious 1.6 hdi was doing regens every 1000-1500kms ..
I am suspecting the car is trying to start the regeneration while i am doing highers engine speeds and loads on the highway, but cant and goes straight in to limp mode …
While i was looking around the menus i also found latest engine cutoff reason .. which is also strange as hell …

Diagbox also seems not to be able to recognize the gearbox ecu when doing initial diagnostics check …
It is the robotic semi-automatic box ..

Anyone having an idea if the 4000 kms since last regen is strange?

Should i suspect some differential pressure sensor fail.. or the hoses getting to it also…?

[LedZep]

4k km seem too much for regeneration. I noticed that the ash level in fig. 3 is 100%. In any case you have to check all the values of dpf like deferential pressure e.t.c. Check this video.

[DimitarK]

Yea that seems also a bit weird because ash level is showing 100%, meanwhile differential pressure is like 2 mbar ..
I guess i will try to reset the dpf interval and force a regeneration ….

To start with

[LedZep]

Yea that seems also a bit weird because ash level is showing 100%, meanwhile differential pressure is like 2 mbar ..
I guess i will try to reset the dpf interval and force a regeneration ….

To start with

Force regeneration is not a good idea. You risk damaging the dpf because of stressing it and maybe crack due to high temp.You have to find the cause why the dpf is not regenerating. I'm not an expert in 1.6 engine but i know that some engines for example use the glow plugs and extra fuel to regenerate increasing temp to flame the ash, other heat with a diesel injector in dpf and other with eolys additive to lower the temperature to burn the ash.Probably even if you try to force regenerate the dpf, ECU won't allowed it because it sees that the dpf is 100% clogged or for the real cause of the problem and wrong values. IF YOU BYPASS BY RESETTING THE DPF LIKE THAT YOU FIT A NEW DPF AND YOU FORCE REGENERATE, YOU RISK EVEN THE CAR TO CATCH FIRE BECAUSE IT WILL INCREASE THE TEMP BY INJECTING EXTRA FUEL TO BURN THE ASH. Because the car is used and you don't know the history of it, be more suspicious because there are NO codes about dpf events even if the deferential pressure is ok. I've heard about a case with "gizmo" installed in can to simulate the right values to ECU that DPF is "happy" to bypass the clogged dpf without changing it for example.Also the fact that there are no codes stored in ecu is another sign that something is wrong.In my lexia all the events are stored every time that i had something going on.Maybe a remap to get rid of emissions codes? Who knows.

[DimitarK]

Ok i took a while since i have reported on the issue.
SO it turned out that the diagbox that i got was not exactly working properly ... it was never able to reset error codes and it simply did not want to do any changes to the actual parameters of the car.
Got a new version installed on a brand new windows and it now seems to be able to reset error codes ... most of them anyway.
I have done the DPF reset interval .. or in other words told it that i have changed the DPF so the kilometers left are back to more than 0

What bugs me a lot is ... the gearbox ecu seems not to be recognized (thats with both the old diagbox and the brand new one) - the car does not use the start-stop system .. and when i took a ride with the pc connected and looking at the start-stop parameters - it does say that the neutral switch is not in the right position ... no matter what i do ... i believe this prevents the car from allowing it to use the start-stop ..
And somehow this may be connected to the problem i get on the highway ... car gets warm and wants to regenerate - but it does not get the allowance from the gearbox ...i believe ... but i can be very wrong ... anyway the limp mode does not spit any error codes out ... and i dont seem to be able to see any saved codes still - that is very very annoying

I have a suspicion that the previous owner has changed the gearbox at some point and never really put it in the BSI configuration ... can that be an issue? Are these gearboxes supposed to have the VIN number set correctly so they can work together with the rest of the car?
The same ECU not recognized is showing up on the RT6 unit and the voltage governing ecu (whatever the hell that is) - the car is able to talk with the battery and the state of charge seems fine ...

Is there a gearbox reset procedure or some way to reprogram the vin number in the gearbox? or the gearbox number in the BSI ..?

[DimitarK]

Ok new update.

Problem is still not fixed and i have not worked a lot on it. But today i decided to check with an old diagbox (7.57)

To start with - the gearbox ecu is not recognized:

Turns out one of the errors on the BSI is showing gearbox communications issues. Error code U1109

Seems like this error is bound to disable the start-stop as well ... and it was confirmed by checking the last few reasons start-stop was not triggered:

My next step will be to try and get a wiring diagram to check the fuses and maybe track a few wires that may have gone bad ... but if anyone has an idea what else i can get into looking - you are more than welcome to shoot here

Does anyone have a wiring diagram available??