Fiat Ducato X250 2008 3.0 160
Following intermittent problems with the dreaded P0638 and having found the throttle body to be badly corroded inside, I have now replaced it with new a like for like replacement.
The fault code was clear and not showing prior to the replacement, however it is registering all of the time now even after being reset and with the engine running and starting all fine. I have checked all of the electrical connections and have found no problems
Can someone please advise if there is a Relearning procedure for a new throttle body or does it need to be calibrated in any way. thanks

Hi andyflan

I have recently replaced the TB on a 2008 2.3 Ducato. As far as I'm aware there is no re-learning or recoding required. This component receives a pulse width modulated signal from the ECU which tells it what flap position to adopt. It also sends a feedback signal to the ECU (Only used on the 3 litre) so that the ECU can check that the position corresponds to what has been requested. I assume you have the correct connectors, and that the wiring back to the fuse/relay box behind the nearside headlamp is all OK with no chafing or corrosion.


I have never got to the bottom of quite how the ECU decides when to flag a P0638 error. I think there may be more things monitored than simply the Throttle Body. The EGR system also includes the EGR valve which in turn is controlled by a variable vacuum from the Solenoid Valve (under the centre of the windscreen). The EGR valve and the Throttle body perform a double act under ECU control, to get the right blend of exhaust gas and clean air into the inlet manifold depending on running conditions, RPM, load etc. Possibly the manifold pressure is monitored to detect problems with EGR operation, and this too could throw the same code ? You might like to check out the thin rubber pipes on the solenoid valve as they can split at the ends. A new solenoid valve is about £60 and is very easy to get at (Unlike the throttle body !). The EGR valves are supposedly reliable.

Today I have also had to replace the TB due to PO638 code
Having previously disconnected the battery for 1 hour, then after reconnecting the engine management light stayed off for a week but then returned. I have a 2009 120 motorhome.
Thank you for all advice on here.

I reset my ecu (much older ducato, no obd port) by disconnecting the battery and switching the side lights on to drain any residual power.

If you have replaced the throttle body I suggest you also replace the solenoid valve referred to by Anthony 489 - with a damaged TB this has to work harder than normal and can fail - this is not my own opinion but that of a very knowledgable guy called Nick something - can't recall if he's on this forum or one of the motorhome forum - but he goes into quite a bit of detail on this matter and recommends that valve replacement. Easy diy job, but also check tubing for splits.

Found him - Nick has the username Euroserv on this forum - lots of advice there as per Anthony489. New TB, wiring adaptor and solenoid valve solved problem with my 2010 Ducato - fingers crossed!