Technical P0236 - boost pressure code info

[Ics19]

'03 JTD 115 - I relocated the boost pressure solenoid valve a couple of months ago as per the guide, following some wet weather floods. It was 3rd to 4th gear changes that triggered the error (resulting in some P0235 & P0236 'invalid signal' codes that eventually left the engine fault light on). These cleared ok with Yani's FIAT Ecu scanner :worship: and I hadn't had a single beep beep beep until last week.

This time it was an instant fault light whilst just doing a steady ~70mph in top and the scanner showed a P0236 with 'low signal' and although it cleared ok, it came back a couple of days later on the same stretch of road. I did the usual connector checks and tubing leaks, but nothing obvious. However, watching the little actuator rod on the turbo showed it not moving at all when the engine was revved and by the looks of wear marks it was "not on" at all - which may well account for some sluggish performance that i'd just gotten used to

Just to confirm my suspicions, I did a short run with the scanner monitoring RPM, Boost control, Boost pressure and Desired boost pressure. It confirmed that the actual boost pressure wasn't hardly moving on my 1-2-3-4 gear change to-end-of-road test and so differred greatly from the desired boost level.

I took the plunge and got a new boost solenoid - what a difference The new boost level now tracked the desired value with a bit of lag and the car was transformed as you can imagine. A quick check of the turbo actuator showed it now moving when revved. I've done a couple of screen captures attached of the before and after runs for info, incase anyones looking to compare.

 

[minimad99]

Interesting stuff Ics19,
Where abouts is the turbo actuator? what does it look like?

 

[Argonought]

I agree - very interesting

Actuator is that device at the very front of the engine that looks a little like a fuel pump. Just follow the overboost tubing and you'll find it

 

[minimad99]

ah, i thought so, should the rod move in and out when engine revved then?

 

[Argonought]

Yes; although not sure it will move that far as the engine's not really under much load.

You should also be able move it slightly with your fingers (quite hard).

Don't think they go faulty very often but some light lubrication may help as it's quite exposed and tends to go rusty.

 

[Ics19]

As Argo says it doesn't move that much when blipped, but at idle you'd expect to see the rod pulled in and this is released when the engine is turned off (although there's a delay of about 10 seconds before the vacuum goes). The travel is about 10mm. The default position with no vacuum (ie safe mode) is the 'minimum boost' position of the variable vane turbo, hence if the solenoid ain't going, things will be sluggish.

 

[tr1s0]

Hi guys, i've been getting a similar problem, where an fault occurs in 3rd 4th and 5th gear but it only happens at a certain rpm. I've looked for any split hoses etc but have found nothing.

When I put the ecu scan on the car, the desired boost pressure and the acctual boost pressure looked very similar to the first graph above so i'm now assuming the boost solenoid is the problem as with yours Ics19.

I will have a look at the solenoid in a bit to see if the rod moves but could you tell me where you got the new solenoid and how much it was.

 

[Hydrocw49]

The solenoid is about £50 from Fiat, going to Fiat you will also get the latest version of the solenoid - I'm on my third (both failures due to puddles!) both replacements were slightly different - the latest though does look to provide a little more protection from water ingress. It is slightly cheaper from europe, but you'll have the hassle of shipping etc - its a lot easier to go to your local Fiat dealer - they've normally got them on the shelf (a common fault!)

You might find that some of the ECU Scan info is a bit misleading - especially the desired boost pressure - even after changing mine, it rarely reaches the desired figure - but I still have excellent boost/performance. You say yours has a fault at the same rpm - does this coincide with anything else? Mine would do it on a certain stretch of road going uphill, which if you immediately lifted and reapplied throttle would clear itself.

Assume you get an engine fault message - what codes did you find when you dd the ecu scan? it should give you a P code and a basic fault description. P0235 is Engine boost condition - limit not reached, ie under boost.


Have a look at the guide I published earlier this year on resiting the solenoid to stop it being drowned everytime you go through a big puddle.

 

[tr1s0]

When I first bought the car last year the first thing I did was move the solenoid so thats not a problem.

It always happens when hitting the rpm's, doesn't matter if its on a flat, hill or whatever. 3rd is about 3750rpm, 4th is about 3250rpm and 5th just under 3000rpm. If you keep the pedal applied, it doesn't effect the power, but if you lift off it cuts the power untill you go under the rpm when the fault comes on or when you change gear.
The fault code that comes up is P0235.

Its not usually a problem as it only usually happens when overtaking or on the motorway but is a pain when it happens.

I unplugged the solenoid earlier to have a look, but all looked ok. Since then i took the car out and it hasn't happend at all, so dont know if there was a loose wire or something. I'll keep an eye on it though and see what happens.

I'm having it up on a ramp tomorrow just to double check if i've missed any thing i.e a split pipe as it seems to whisle a bit.