Technical P0638 Throttle Actuator Control Range

[rolopolo]

Have you checked the wiring looms where they connect the ecu?
One of them rubs against the steel tube it's cable tied too.

After new throttle actuators, turbo, we found the tiniest of pin prick holes, where water had gotten into the wire core, corroding over time, gradually getting worse. New loom was made up, all sweet

 

[John Dough]

Well light came back on just after DOE! but still not happy as engine still sluggish at times disconnected throttle lead completely very bad pulling power but still goes to idle and won't rev so bit the bullet and bought a new throttle body with loom.
Well whole front has to come off to get to lower bolts ,top two came off ok but bottom ones rock solid soaked in pen oil /wd40 for 2days still no budge.
So a ex fiat mechanic said just let them wring off and so they did!!

What a load of s**t in the manifold took a couple of rags to get it all out as clean as possible.

No problem he says just drill out old bolts and use new helicoils so he helped me out there as he had a complete kit of them.A little tricky lining up new valve but got there eventually and hey presto like a new engine gave it a huge difference.

The bottom bolts were corroded solid from the constant water dropping down from the scuttle panel also some components very rusty (injectors etc.) but would not dare touch them when running ok.Drilled a couple of extra holes in the scuttle panel to drain the water out of harms way but what aa crappy design from Fiat whic was never modified.
Cheers.

 

[wattoo]

Cheers Rolopolo, I have checked wiring completely back to ECU in the past, spent a couple of days on it. Even replaced the wires with jump wires to rule out the loom.

 

[wattoo]

Forgot to say that the engine had 2 glowplugs that had snapped off, so from my experience with other makes I decided to rule these out by drilling out the snapped ones with the owner & replaced them with new ones. It didn't stop the throttle body fault, but will make starting easier.

If anyone wants any tips on glowplug removal in these just ask

 

[corcai]

If the intake is that full of crud I would suspect the egr is stuck / sticking that will throw the expected MAF reading too as will choked intake ports.

 

[wattoo]

EGR new in my case and no clogged system

 

[corcai]

EGR new in my case and no clogged system

I was referring to John Dough saying the intake was full of crap.

In your case it might be worth sanity checking the actual MAF reading from RPM IAT MAP Displacement and a ball park figure for volumetric efficiency.

e.g.

(MAF [g/s] = Mair ∙ Vd ∙ nvol ∙ (MAP – (patm/CR)) / (R ∙ IAT) (1)

linky

 

[wattoo]

Apologies!

Thanks, that's interesting will try to work it out from the formula. If MAF sensor is reading incorrectly it would obviously trigger a fault, likewise of the others mentioned in the formula.

 

[John Dough]

Where is the EGR located on the engine m8? after throttle valve??

 

[Banjobob]

Don't know if this helps. But here's a video of me cleaning my throttle body.. EML hasn't shown up since!... just clean all the gunk around it
[ame]https://youtu.be/ZN1QFmQKreg[/ame]

 

[wattoo]

Finally got this problem sorted....no surprise though, it needed a new modified throttle body. The Wahler unit failed inside the electrical half, and no sign that water had got into it. I suspect these seize up and something blows on the circuitry.
The modified throttle unit's flap is much more sturdy, in a better open position (allows optimal airflow where the Wahler is slightly off fully open). As the new unit has dropped in price and is about £300 cheaper than from the dealer, it was time to try one as the only other possibility was a faulty Injection ECU.

I used a Launch Creader VIII for the diagnostics, as this shows Target Air Mass and Actual Air Mass readings - a good hint that if mis-matched then there is an airflow problem or a sensor fault. Whereas previously I could only get the Mass readings to match by removing the electrical half of the throttle body & turning the flap manually, the new throttle body (once fault has been reset) matches the target mass figure correctly.

To help others with diagnosing what the fault cause is, here's some live data of a good engine with new modified throttle body, so you can compare yours with this engine.

All figures engine idling & cold, ambient temp 21ºC

Target Air Mass: 282mg/injec.
Air Mass Measured: 291.50 mg/injec. but accurately follows target figure
Atmospheric Pressure: 1019mbar
Air Temp (Air Flow Meter): 25.56ºC
Throttle Solenoid Valve opening: 87.06%
Throttle Status: In Correct Positiom *** please not this says the same if the old faulty Wahler unit is fitted so don't rely on this reading to assist you! ***

Also the new throttle body behaves differently to the Wahler unit, it flips shut then open after ignition is turned on, and can be seen to operate as the spindle end is exposed on these. There is a strong return spring also, which will assist in keeping the valve in the open position, unlike the Wahler unit.

Happy Days

 

[andydiver]

Another fix for Error code P0638. My van was getting a little worse with engine hesitation under load throwing this fault for a long time previously every now and then. There is a multi pin connection buried in the fuse box next to the air filter. The wires from the throttle valve buzz to there. The connection is likely to have sat in water over the years as is at bottom of plastic tray. Open up, find corrosion, scrubbed up and hopefully fixed. See pics. Likely a cause for other issues!!!
Had to follow the engine loom and it divides, one spur to a connection on the Ecu, the other spur loops round into the Base of that box and the connectors you see pulled up.

 

[SailorBob]

2010 Fiat Ducato Multijet 120 2.3L Turbo Diesel Manual Transmission

I've got this code popping up and recorded some data at cold start and warm start.​

On the cold start the Target Air Mass is steady after the initial burst, but the Solenoid Opening and Air Mass Measured oscillate for a bit till the solenoid ostensibly goes to 5% and the Air Mass Measured sticks at about 500mg while the Target is about 300mg. After I tap the accelerator, the measured and target air masses match more or less.

On a warm start I just get a mismatch between the measured sticking around 500mg and the target around 300mg, which again resolves​

after I tap the accelerator pedal.

I've also noticed sometime hard hesitation going uphill, but it's not consistent and I haven't been able to record it yet.

My first question would be how difficult is it to get the throttle body out on the 2.3L engine? Does this seem like it might be sticking due to being dirty, or maybe it's just worn out? I've got 434,000 kilometers on this thing. I've also got some weird electrical issues on this vehicle as some of you may already know from my other posts. One other tidbit, I only started getting this DTC after I had my transmission replaced, maybe just coincidence or maybe they accidentally knocked something around...​

 

[LandyAndy]

What throttle body do you have. The old original or the updated version?

 

[SailorBob]

What throttle body do you have. The old original or the updated version?

I'm pretty sure it's the original that came on the engine, but I'd have to go over all the service records the seller gave me to be sure.

I recorded some more data on a cold start this morning. I had a dead no start at first, but then it started up and I got even stranger results:

As soon as I put the key in the run position, before starting the vehicle the Valve Opening showed it oscillating between 0 to 5% open and Throttle status was switching between Open and In Error. Once I started the vehicle both those values kept oscillating wildly, but the Target and Measured Air Mass where both matching and stable and the RPMs where stable. You can see the oscillations better here:

Obviously this seems like an incorrect reading, because if the Throttle Solenoid was actually bouncing between 0% and 90% open the RPMs and Measured Air Mass would be wildly swinging as well...

So an electrical problem?

 

[Anthony489]

Hi SailorBob

To answer your question about removing the Throttle Body on the 2.3 engine, I have done this a couple of years ago. This forum post gives the details: https://www.fiatforum.com/threads/p0638-logged-ocasionally-ideas.481962/

To summarrise, it is do-able but a bit of a faff and you need to be able to cope with the likelihood of one or more bolts shearing off in the manifold and needing helicoiling.

Probably worth noting that the Throttle Body is "open loop" i.e. there is no electronic feedback to the ECU about what it is doing. Nevertheless, the ECU seems to be able to tell if all is not well with the TB and throw a P0638 code, presumably by taking inputs from other sensors and seeing if behaviour is as expected.

In my case, the TB looked OK but replacing it stopped the fault being logged again.

 

[0ldie]

Thanks to all those who have contributed to this PO638 problem. I have no mechanical knowledge so will take the vehicle to a Fiat Service Agent.
A number of local service people don't want to touch this problem as they find getting Fiat parts a problem.
Could be an expensive fix! Have had the Ducato 3lt since new in 2011. Situated in New Zealand at KeriKeri in the Far North. Safe driving to all.