Fault code P0638

[tidewatcher]

On my 2007 2.3 Ducato, there is 2 rubber pipes going to the valve under the scuttle of which you write. It is very easy apparently, according to others, to put these the wrong way round and even if correct, it is advised to replace this valve at the same time as the TB because, it has been working overtime try to rectify faults on the old TB + check there is no holes or leaks on the 2 rubber pipes.

I have, so far, had no problems with my old TB but have been carrying a new one around for the past 5yrs just in case?

The advice in the first paragraph, is advice I've read from MMM magazine experts, not from personal experience.

Good Luck!

Fitted a new scuttle valve which made no difference, did check the pipes for leaks but will try reversing them just in case. Also tried the old valve again just in case the new one was faulty but no change. Thanks for the reversed pipes info.

 

[tidewatcher]

Tried the reverse pipes and no change, in fact it made no difference whichever way the pipes were on, still hinting on tick over. Hey Ho. Thanks anyway.

 

[tidewatcher]

OK now reaching my limits.
Can anyone explain exactly how the system works?
The throttle body butterfly is part closing in time with the engine tick over hunting. What is telling it to operate? What signal is going to the management system telling it to open and close the butterfly?
The egr valve is controlled by the vacuum pipe which is controlled by the egr solenoid valve. What signal to the management system tells it what to do?

Does the 2.3 iveko engine have a particulate filter and if so where is it? Changing the egr valve is pretty tricky access wise and is getting beyond my abilities. Th e only real clue to it being the egr valve is that the tick over stabilises when I blank the small vent pipe at the bottom of the egr solenoid valve but is that because the egr valve is stuck or an I overriding a signal to the solenoid to operate. I cannot work out what is a cause and what is an effect.
Thanks for all the help but now feel it is getting beyond me.

 

[Landy Andy]

From my knowledge, which is based on my 2.3 2010. The ecu controls the TB and the EGR valve together as a pair. So I would suggest that if your TB is closing due to being commanded it will be because the ECU wants to operate the EGR.

Are you 100 percent sure your EGR is operational?
And that it can fully open when a vacuum is applied to it, and shuts fully when vacuum removed from it.

It is odd (wrong) that it is choosing to use the EGR system whilst just ticking over. But if it is, and the EGR can open it should not cause a misfire as it can take air supply from exhaust. It would initially appear your EGR isn’t opening so starving the engine of air when it closes the TB. But I still struggle to understand why EGR is being operated at tickover.

It would be nice to get a scan tool and understand IF the ECU is trying to use the EGR or not.

There are two other options though. Have EGR removed from the ECU, cost about £150, or remove the butterfly from the TB spindle. Cost 0. That way the van thinks it’s doing something but isn’t.

 

[tidewatcher]

From my knowledge, which is based on my 2.3 2010. The ecu controls the TB and the EGR valve together as a pair. So I would suggest that if your TB is closing due to being commanded it will be because the ECU wants to operate the EGR.

Are you 100 percent sure your EGR is operational?
And that it can fully open when a vacuum is applied to it, and shuts fully when vacuum removed from it.

It is odd (wrong) that it is choosing to use the EGR system whilst just ticking over. But if it is, and the EGR can open it should not cause a misfire as it can take air supply from exhaust. It would initially appear your EGR isn’t opening so starving the engine of air when it closes the TB. But I still struggle to understand why EGR is being operated at tickover.

It would be nice to get a scan tool and understand IF the ECU is trying to use the EGR or not.

There are two other options though. Have EGR removed from the ECU, cost about £150, or remove the butterfly from the TB spindle. Cost 0. That way the van thinks it’s doing something but isn’t.

Thanks. I cannot work out only assume the egr valve may be sticking, the fact that the tick over misfire clears at 1500 rpm hints that way. While the TB was off I changed the boost pressure sensor as a precaution, could a fault there cause this sort of problem? As I mentioned it all points to the egr valve but I do struggle with the logic.

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[L' Hobo]

From my knowledge, which is based on my 2.3 2010. The ecu controls the TB and the EGR valve together as a pair. So I would suggest that if your TB is closing due to being commanded it will be because the ECU wants to operate the EGR.

Are you 100 percent sure your EGR is operational?
And that it can fully open when a vacuum is applied to it, and shuts fully when vacuum removed from it.

It is odd (wrong) that it is choosing to use the EGR system whilst just ticking over. But if it is, and the EGR can open it should not cause a misfire as it can take air supply from exhaust. It would initially appear your EGR isn’t opening so starving the engine of air when it closes the TB. But I still struggle to understand why EGR is being operated at tickover.

It would be nice to get a scan tool and understand IF the ECU is trying to use the EGR or not.

There are two other options though. Have EGR removed from the ECU, cost about £150, or remove the butterfly from the TB spindle. Cost 0. That way the van thinks it’s doing something but isn’t.

Much has been spoken about TB, EGR and ECU but, so far I don't think, about the MAF? sensor that sits near the air FILTER and measures the air flow, could that have a bearing on the tickover?

 

[Landy Andy]

The MAF has been swapped I believe, but on a diesel it won’t alter what the TB is doing. The MAF provides information to regulate the amount of fuel to the air, so MAF controls injectors, not the TB.

Although the MAF would/should indicate information showing what is going on, but would need a know good value from a healthy engine to understand its differences. The same could be said of the MAP sensor which you would think to be struggling currently with having its air supply removed.

 

[Landy Andy]

tidewatcher

If you have the ability to clear code then try this.

Remove the electrical connection from the EGR vacuum solenoid. This I believe will disable the EGR system. But will bring on a code, and its warning light. Then take for a test drive and see how van drives without the EGR system and see if it has stopped the TB fluctuating

 

[tidewatcher]

Much has been spoken about TB, EGR and ECU but, so far I don't think, about the MAF? sensor that sits near the air FILTER and measures the air flow, could that have a bearing on the tickover?

In fact I changed the MAF as I always carried one as a spare so thought it would at least eliminate that as a possibility. No change in tick over so at least we know it’s not that! Thanks.