2008 Fiat Scudo Overboost error code
Discussion
Arrrrgggghhhhhhhhhh
I'm new here so thanks for having me and apologies for starting with a Fiat 2.0Hdi problem.
I'm getting Limp mode with error code P0234 (Turbocharger"A" Overboost ) no other codes when all is connected, I've got an ODB reader with live data (limited) which shows my MAP being 104Kpa at idle, acclerating in 3rd up a hill (repeated route to test) trips into Limp Mode with P0234 and way over 220Kpa. So its not releasing pressure to be expelled by the exhaust)
So i've checked the wiring,the vacuum hoses, the vacuum pump output and replaced the Boost Solenoid ( the old one was very draggy) all to no avail.
I pulled the turbo out yesterday (no easy task on a Scudo) give it a good clean, found a sticky Vane. Reassembled it and it's working very smooth (the vanes are moving freely with no resistance). I tested the actuator using a vacuum pump and it works OK(ish), its a bit wobbly and the first 5mm or so is loose ( when not unde pressure), it takes a bit of pressure to get it going (about .3bar , reaching maximum at about .8bar).
I'm at a loss as to what to do to be honest, my instinct its the Vacuum Actuator is at fault as Its very slow to do anything (I've also observed it on the van during start up and it barely moves.
Anybody got any help they can throw my way?
I'm new here so thanks for having me and apologies for starting with a Fiat 2.0Hdi problem.
I'm getting Limp mode with error code P0234 (Turbocharger"A" Overboost ) no other codes when all is connected, I've got an ODB reader with live data (limited) which shows my MAP being 104Kpa at idle, acclerating in 3rd up a hill (repeated route to test) trips into Limp Mode with P0234 and way over 220Kpa. So its not releasing pressure to be expelled by the exhaust)
So i've checked the wiring,the vacuum hoses, the vacuum pump output and replaced the Boost Solenoid ( the old one was very draggy) all to no avail.
I pulled the turbo out yesterday (no easy task on a Scudo) give it a good clean, found a sticky Vane. Reassembled it and it's working very smooth (the vanes are moving freely with no resistance). I tested the actuator using a vacuum pump and it works OK(ish), its a bit wobbly and the first 5mm or so is loose ( when not unde pressure), it takes a bit of pressure to get it going (about .3bar , reaching maximum at about .8bar).
I'm at a loss as to what to do to be honest, my instinct its the Vacuum Actuator is at fault as Its very slow to do anything (I've also observed it on the van during start up and it barely moves.
Anybody got any help they can throw my way?
Thanks for the replies and sorry for taking so long to reply myself ( the forum wouldn't let me).
Yeah it's a bit turbo, since my first post I've replaced the turbo as there was little damage to it and the actuator wasn't working correctly. Unfortunately I'm still getting the p0234 overboost error and limp mode.
There a no breaks in the vacuum lines but the fitting onto the actuator isn't as tight as the other fittings, could it be leaking out of there as the vacuum is applied?
Yeah it's a bit turbo, since my first post I've replaced the turbo as there was little damage to it and the actuator wasn't working correctly. Unfortunately I'm still getting the p0234 overboost error and limp mode.
There a no breaks in the vacuum lines but the fitting onto the actuator isn't as tight as the other fittings, could it be leaking out of there as the vacuum is applied?
forum locked out again 
anyway, its quit difficult to access the actuator and the hose as its down between the back of the engine and the bulkhead( its all done by feel).
I've pulled the vacuum hose off and there's a difference in size from one end of the rubber piece (the hose has a rubber section at each end of an aluminium pipe) so im waiting for some vacuum hose to replace them and see if that helps.I did try driving without the MAF as sunbeam alpine suggested may be the problem but to no avail.
While I wait for the hose anybody want to point me in any other direction? Most of the other common problem (blocked intakes etc) seem to cause low boost rather than overboost but I'm open to any suggestions
again thanks for your help
anyway, its quit difficult to access the actuator and the hose as its down between the back of the engine and the bulkhead( its all done by feel).
I've pulled the vacuum hose off and there's a difference in size from one end of the rubber piece (the hose has a rubber section at each end of an aluminium pipe) so im waiting for some vacuum hose to replace them and see if that helps.I did try driving without the MAF as sunbeam alpine suggested may be the problem but to no avail.
While I wait for the hose anybody want to point me in any other direction? Most of the other common problem (blocked intakes etc) seem to cause low boost rather than overboost but I'm open to any suggestions
again thanks for your help
its just vacuum from the vacuum pump, theres a hose from the pump to the N75 Solenoid, then this hose from the N75 to the actuator, im trying to wrap my head around whether there is vacuum at idle or whether it as applied to reduce boost, i will add its difficult to determine when the vacuum is being applied/shut off as my manual gauge has no way to be fitted and viewed whilst the engine is running at anything other than idle. I've got some t-pieces and some extra hose coming so I can rig it up to be in the van when i'm driving it 
Edited by Spev11 on Friday 26th October 14:09
engine load makes more sense yes
I don't have the means to interrogate the ECU to find out what the activation levels are, the diagnostic (a D900) i have is quite basic but does have live data (but only shows load, revs, MAP and MAF). If I were to at least fit a vacuum gauge it would show me at what revs/load/MAP setting the vacuum was being applied/shut off wouldn't it?
I'd happily invest in something a little better if someone could point me in the right direction
I don't have the means to interrogate the ECU to find out what the activation levels are, the diagnostic (a D900) i have is quite basic but does have live data (but only shows load, revs, MAP and MAF). If I were to at least fit a vacuum gauge it would show me at what revs/load/MAP setting the vacuum was being applied/shut off wouldn't it?
I'd happily invest in something a little better if someone could point me in the right direction
Cheers for all the info, ive just made up some vacuum hoses to test the various inputs and outputs.
Ive had a look at diagnostic and few people support the siemens ECU in the PSA vans, i've found a cable and some software that can read the ecu so as soon as that arrives i'll be reading that.
Many thanks for all your help and i'll update you when something happens
Ive had a look at diagnostic and few people support the siemens ECU in the PSA vans, i've found a cable and some software that can read the ecu so as soon as that arrives i'll be reading that.
Many thanks for all your help and i'll update you when something happens
My Lexia3 has finally arrived, getting the laptop sorted now to check the ecu out.
I replaced the Solenoid with the correct one and its all been ok for the last week or so until tonight driving home and P0234 popped up on my diagnostic so I'm back at the start again. Once i've got the lexia installed and working I should be able to see whats going on
I replaced the Solenoid with the correct one and its all been ok for the last week or so until tonight driving home and P0234 popped up on my diagnostic so I'm back at the start again. Once i've got the lexia installed and working I should be able to see whats going on
While im waiting for the install of lexia diag on my laptop (its deathly slow) i've been running vac tests on the van and checking some other things.
So far I've discovered that :-
a.The solenoid works when I apply power to it (no vacuum allowed with no power, vacuum allowed with power)
b.the solenoid is allowing boost all the time ( vac gauge shows 1 bar regardless of load/revs etc)
c.the solenoid doesn't shut down the vacuum at any point that I can see.
d.If I introduce a bleed/leak to the hose from the solenoid to the actuator the van runs, I have boost but it doesn't drop into limp mode (its not as mental quick as it was when it was keeping the actuator open)
e.Hopefully once I get this diagnostic software running I'll be able to see why the solenoid isn't being switched)
as for point d is there any danger to the van if i run it in this mode whilst I find out what the problem is? I'm not intending to leave it like this but I need to use the van for work (short journeys for now until I find a solution)
So far I've discovered that :-
a.The solenoid works when I apply power to it (no vacuum allowed with no power, vacuum allowed with power)
b.the solenoid is allowing boost all the time ( vac gauge shows 1 bar regardless of load/revs etc)
c.the solenoid doesn't shut down the vacuum at any point that I can see.
d.If I introduce a bleed/leak to the hose from the solenoid to the actuator the van runs, I have boost but it doesn't drop into limp mode (its not as mental quick as it was when it was keeping the actuator open)
e.Hopefully once I get this diagnostic software running I'll be able to see why the solenoid isn't being switched)
as for point d is there any danger to the van if i run it in this mode whilst I find out what the problem is? I'm not intending to leave it like this but I need to use the van for work (short journeys for now until I find a solution)
Yeah its pulling vacuum all the time. I've tested the solenoid by putting the gauge on it and putting power through it and it switches on and off ( the old one does as well but it sticks sometimes hence me buying a new one)
I've finally got the software installed so tonight i'll make a start on checking the ECU to see what its doing (or not doing)
i've also got a couple of fuses out, one for the power steering (easy enough) and the fuse for the relays that switch the aux cooling fans on and off (they also cool the intercooler) so maybe having an influence on it (prob not but I'll clutch any straw at the moment)
also thank you for all your help so far
I've finally got the software installed so tonight i'll make a start on checking the ECU to see what its doing (or not doing)
i've also got a couple of fuses out, one for the power steering (easy enough) and the fuse for the relays that switch the aux cooling fans on and off (they also cool the intercooler) so maybe having an influence on it (prob not but I'll clutch any straw at the moment)
also thank you for all your help so far
I get what your saying but both solenoids open to allow vacuum ( or blowing when I'm testing on the workbench) when I put power through them and close off when I remove power, I can feel and hear them opening and closing.
It would appear that the ECU is switching power on but not off ? If that's a possibility, I'll know for sure once I get the diagnostic on
It would appear that the ECU is switching power on but not off ? If that's a possibility, I'll know for sure once I get the diagnostic on
ah to make it clearer, when the solenoid is on the car and wired up (all pipes in the right places) as soon as I start the engine my gauge shows vacuum (almost 1bar, same as outputting from the pump), using a test meter I can see voltage on the supply lead to the solenoid, hence it being "open" making me suspect the ECU at the moment. just adding this as Im not sure I made it clear (my head is fried from working and then trying to sort this out)
cheers Steve, im in work at the moment but as soon as I get home I'll try that./
The diagnostic software has done an actuator test (i run it quickly late last night) and all solenoids and actuators are working when the ecu is instructed to open/close them. I only had a brief look at various things, i took this screen shot of the air intake information page, don't know if its of any help? I'll be checking it all properly this afternoon.
according to my manual the turbo pressure ref value of 1bar is correct (but at 4000rpm) so the turbo pressure at 750rpm of 1 bar is too high maybe?
sorry if I'm being dull
The diagnostic software has done an actuator test (i run it quickly late last night) and all solenoids and actuators are working when the ecu is instructed to open/close them. I only had a brief look at various things, i took this screen shot of the air intake information page, don't know if its of any help? I'll be checking it all properly this afternoon.
according to my manual the turbo pressure ref value of 1bar is correct (but at 4000rpm) so the turbo pressure at 750rpm of 1 bar is too high maybe?
sorry if I'm being dull
boost wasn't following target, reading approx 200mbar over at any given point other than idle, so had a proper good search of various image galleries to discover that the third output/input on the solenoid (mine has a blanked off hose on it which has been on there since I bought the van) should have a one way breather on the end ie.
This is to allow the vacuum to bleed off in a timely fashion (the vacuum tester I used was showing it taking quite a while to bleed off when the vacuum was shut off) rather than too slowly (which is causing my overboost problem). As the old actuator was faulty I suspect that's why It never happened with the blocked off hose (actuator leaking the vacuum away)
So after weeks of rebuilding stuff (some necessary some not) it looks like Its all working (a tentative test drive yesterday showed the boost following the target and no errors)
Many many thanks for all your help Stevieturbo and others.
Off to fix the open circuit on the cooling fan now ( some things never end)
This is to allow the vacuum to bleed off in a timely fashion (the vacuum tester I used was showing it taking quite a while to bleed off when the vacuum was shut off) rather than too slowly (which is causing my overboost problem). As the old actuator was faulty I suspect that's why It never happened with the blocked off hose (actuator leaking the vacuum away)
So after weeks of rebuilding stuff (some necessary some not) it looks like Its all working (a tentative test drive yesterday showed the boost following the target and no errors)
Many many thanks for all your help Stevieturbo and others.
Off to fix the open circuit on the cooling fan now ( some things never end)
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