Hello All. I have a 2008 2.3 X250 Ducato (120 HP Euro 4). Three times in the last 12 months I have had a P0638 error come up ("very low signal from sensor"). Also a slightly erratic power delivery when accelerating hard above 2500 RPM. Each time it has happened during rainy weather, though this may be a coincidence. Idling is fine, and power is more than enough to do 70 MPH on the level.


This vehicle is normally stored under cover, and the scuttle is well sealed. So the under bonnet electrical connections all look like new when the plugs are removed. The throttle body flap seems to move easily with the fingers, a light coating of black oil was wiped off. An actuator test with MultiECUscan gave the expected flap movement. Throttle body is the original 2008 Wahler, a design which has no feedback, so the ECU can't know directly what it's doing.


The EGR solenoid valve shows the right electrical resistance and the vacuum hoses look OK. It also makes the usual buzzing noise.


On two of the occasions MultiECUscan has logged the P0638 fault at idle speed and when the engine isn't far off cold (35C), so I'm guessing it happens at a junction or roundabout about 5 or 10 minutes after the first startup of the day.

I cleared the last fault and tested it on the driveway off load, with spells of idling interspersed with blipping the throttle. This showed the Throttle valve and EGR valve percentages varying, so the EGR system is activated and trying to do something.

My suspicion in that the throttle valve is occasionally sticking, but before I fork out hundreds of pounds for a new one, does anyone have any ideas what's going on ?

These might help, particularly the comments by Euroserv who maintained a fleet of Ducatos and knows his stuff.

I know that the throttle body was a recognised weak point on the original X250s and was modified in later production, so is worth replacing if at all suspect.

Deleted post (Reread Anthony's post and he has already done what I was suggesting!)

Thanks for the link to spare parts. The Throttle valve is listed on the Intake Manifold sub-page as Part 7, Electro Valve, 504 345 920 at 644 Euros.

https://www.fiatforum.com/showthread.php?t=464795

This is it. Bad connection, most likely, but also elsewhere in looms if you are not lucky.
If you replace the throttle body you should also repair or rewire in a new loom connection block
Should add, cleaning the existing connectons might work for a while, and this was on my van exact same age as yours. Search P0638 more on the forum and you will find various references to the same.

Some pics. I was able so source an old style body with the same actuator, as I noticed it is possible to replace the actuator from underneath the body without removing the whole valve unit, which requires removing front panels and such.
A new style one should come with a different connector, and a flying lead to connect to your existing one, which is is misleading as the loom block on your old loom likely needs replacing too. I would cut the wires and solder in the new loom block.

Hey Andy, would you happen to have a part number for the actuator?

My 2014 3.0lt 180 Multijet is having the same issue as you described above but without the rain and my van eml comes on at 80-100kph and around 2000rpm. Turning ignition off and on returns normal function.

I have an obd scanner that has shown p0091 from when it first occurred.

Have had van in at a fiat mechanic and they have replaced a fuel pressure regulator and intank fuel pump after which I'm getting p0638 and my problem still exists.

"Also a slightly erratic power delivery when accelerating hard above 2500 RPM. Each time it has happened during rainy weather, though this may be a coincidence. Idling is fine, and power is more than enough to do 70 MPH on the level."

WHALER 7497D Throttle body. Got it on Ebay for £199.
This one. https://www.worldcarparts.co.uk/throttle-body-for-fiat-ducato-iveco-daily-wahler-7497d.

They are getting very rare as the new ones as above retro fit, you simply have to inspect All of the wiring through the looms also.

Your symptoms are exactly like mine were.

An update.

I decided it would be best to replace the original Wahler throttle body with a new Marelli one (£150), plus a short 3 wire adaptor cable (£28) to join the 6 pin Marelli connector to the 4 pin original loom. I also needed a few metal gaskets and 4 new bolts (£13).


The job was a bit time consuming, but straightforward (with one exception). The plastic upper and lower grilles have to come off. The upper slam panel unbolts and swings to one side, no need to detach bonnet release. This gives enough access to unbolt the throttle body, having first detached both ends of the stainless pipe from the EGR cooler. I needed to use a 6 point 3/8 " drive socket with a wobble bar.

Not unexpectedly, the bottom left bolt which goes into an open tapped hole had corroded in place and despite heat and plus gas the head snapped off before it would shift. I had to drill out the centre of the bolt, using a drill guide made from a 1" thick block of aluminium. I was lucky that this operation was accurate enough to leave just a spiral of steel thread in the hole, which could be unpicked with pliers and the alloy thread then cleaned out with an M8 tap. I bought a helicoil kit just in case, but didn't need it.

To give just enough extra room for the cordless drill body, I had to detach the driver's side cooling fan (1 screw, 1 catch then rotate bayonet style) and move it aside, then ease the radiator forwards an inch or two against its hoses. No need to drain the coolant or the air conditioning.

Having cleared the error code with MultiECUscan, the error hasn't yet returned, but I have only done a couple of trips so far so will have to wait and see. The engine also seems to switch off with less of a shudder, so maybe the Wahler valve wasn't closing properly on switch-off.


I also checked the solenoid valve by temporarily teeing in a vacuum gauge on the output port. The vacuum changed in accordance with the EGR percentage reported by MultiECUscan, so I assume it's working OK.

Interestingly, the EGR system appears to normally sit at 5% throttle, 0% EGR when idling. Once the engine is revved off load, the throttle and EGR change to a varying percentage of typically 40 to 60%. After returning to idle, they continue to do their stuff for exactly one minute, then revert to 5% and 0% at which point the sound of the idle (but not the speed) changes very slightly.

I examined the old Wahler throttle body. The flap moved under finger pressure with no sticking against the spring. The electronic circuit board and heatsink were potted, with no signs of moisture. The internals of the "motor" have an O-ring seal and were clean and bright. The flexible coupling and return spring sit in a cavity which is unsealed, and had some sticky black deposits round the outside. Hard to see if these are condensed oil vapour from inside or seeped in oil from outside. Not enough to prevent free movement though.

I can only conclude that despite appearances, the Wahler throttle body has an internal electrical or mechanical fault. Alternatively, I may be getting a P0638 again before long and will have to continue the hunt !

One other thing I did check out was the +12V feed to the Throttle Body. This comes from 15 Amp fuse F11 in the B001 Junction unit behind the nearside headlight. This Fuse supplies "Electronic Injection System Secondary Services", and also supplies power to the Solenoid Valve, the Glow Plug Controller, the Lambda Sensor and the Oil Vapour Heater. This last item appears to be a 20 watt resistor mounted in one of the breather pipes and is fitted in vehicles for northern europe. I disconnected it in case it had an intermittent fault.

Thank you for the detailed update. I did consider replacing the whole unit and in fact removed some bolts from the front metalwork, could not at all see how it should be done! So you don't need to remove much then, well done.
It would be a great help if you could take a couple of pictures of the bolts / sections you moved....

My old throttle actuator was in much worse condition than yours, It is possible there were multiple faults on mine wiring + actuator itself.

Hi

The order of disassembly is:

1.) Remove the plastic upper grille. This has 4 off T30 torx screws with large heads along the top, and a couple of plastic rivets (unscrew the middle then pull out) at the bottom. The rest are concealed plastic pegs. You need to pull the top of the grille forwards towards you by an inch or so, then pull the whole thing upwards.

2.) Remove the plastic lower grille. This has 18 off T30 torx screws. There are also concealed plastic peg fasteners at each side which engage with the plastic side bumpers. Once the Torx screws are all out, again you need to pull the top forwards and then the whole thing upwards.

3.) Remove the slam panel (black painted steel pressing). This has 6 off M6 bolts into the bodywork. You also need to take off the two M8 bolts holding the radiator upper brackets. Then the panel can be sung away and held with a bungee, leaving the bonnet release cable attached.

See the attached pictures.


With these three out of the way, you should have just enough room to get to the Throttle body bolts. The 3 litre is a different shape to the one on the 2.3 and a bit easier to access.


If you need more room, gently pull the top left of the radiator/evaporator/intercooler assembly against its hoses, and wedge it with wood between the engine block and the back of the rad.


For even more room take out the radiator fan and shroud from the drivers side. This has one T20 screw and a plastic release catch hidden away low down. Once these are dealt with, rotate the fan and shroud by an inch or two to release it, no need to detach cable.

Can't thank you enough, great. It's the concealed hook type engagements that get the unwary and never seen it documented so well.

Thanks for the info gents.

Hey guys, I removed the throttle body intake pipe over the weekend to see how it looked inside.

Upon opening it up, the butterfly was almost fully open and was a bit gunked up but the butterfly still had range of motion from fully open to fully closed when manually actuated.

So, quick question, should the butterfly return to fully closed when the engine is shut down?

With the engine off, it does click and the butterfly tries to move about 20 seconds after switching engine off, but no more than maybe 5mm.

I'd post a picture but haven't got enough posts to do so.

Cheers Michael

Hi DSDRBozzy

If you have the original throttle body made by Wahler (with the actuator assembly on the underside) it uses a flap which is sprung loaded open, and a stepper motor which has a 90 degree range of movement.

You should be able to completely close the flap smoothly and easily against its spring using one finger. With no DC power applied (engine turned off and wait till relays drop out) there is nothing to work against the spring, so the flap should be sitting fully open.

When the engine has been idling for at least a minute, the throttle flap should be 5% open. Once you rev up and the EGR system gets going, it will be typically 30 to 70% open.

When you switch off, the flap closes to 0% to cut off the air and prevent shudder. It then returns to 100% open once the DC power disappears.

A light black oily residue is normal, but not lots of sticky deposit.

The later design of throttle body made by Marelli seems to use a geared servo motor with no spring. Once the DC power is removed the flap just stays where it was last positioned.

Since replacing the Wahler body, I have had no more errors logged in the last 600 miles, so can only assume the Wahler had deveolped a fault even though the flap moved easily and ostensibly it was working OK.

Thanks Anthony, mine is a Pierburg TB with the a 3 pin connector on top, it doesn't close to 0% upon switching the engine off.

Hi Anthony. Very interesting, exactly what I was looking for. So, I checked mine.Obviously I had to take off the top turbo hose so not sure if that would effect the movements you mention. Mine followed what you said except for when revved the vane/butterfly closed fully, not open 30-70%. AS I have a black smoke issue on chnaging gear up and down, would this indicate some obvious error (EGR/Sol vacuum valve, etc)? Thanks, Chris.

Thanks for the above as it assisted me today removing my throttle body, which included the apparent standard snapping of the “hidden” bolt. This for me then showed my egr valve has been jammed open, probably for all my ownership, and due to this a quantity of shite in inlet system. I think I will now block off the planet saving system, that has been ruining my engine, and my free time.