Hi, I've read a lot about this issue on this forum so I decided to sign up...
I have a 2007 Citroen Jumper 3.0 with the famous P0638 code. Went to the dealer and he offered a replacement for 700€. I decided to do it myself so I ordered a Pierburg replacement.
I dismounted the old unit and it was completely corroded. I tried refitting it and testing it using 12V supply and Arduino generating a PWM signal but it seems to have some failure anyway (the valve still kicks back to the open position and then starts beeping continuously)...
Anyway I fitted the new part this weekend, but to my surprise the MIL came on right away. The engine starts but runs in limp mode. There seems to be no movement going on in the valve... I disconnected the battery for several hours and removed the error code using Car Scanner on my phone, code comes back right away... I removed it again and tested in on the lab bench using same methods as the old one: it doesn't do anything, no current draw, no movement, no resistance when moving the valve. And the status pin 4 is not connected on this newer unit.
I'm thinking the new unit may be faulty as well...

I ordered another new Pierburg throttle body today together with the newer cable connector from another store, which I can send back no questions asked.

I'm wondering if I did something wrong. On the signal pin 1 from the ECU I measure 3.75V DC and no PWM signal (I checked with an oscilloscope)
All help is greatly appreciated!

Hi Nigelvan

I assume your van is fitted with the Fiat/Iveco 3.0 litre engine. Up to 2009 these were fitted with Wahler 7532D throttle bodies (TB), which suffer from water ingress and corrosion. Later vans had the Pierberg 7.01754.10.0 TB fitted. These can be retrofitted to the earlier vans, but because the connector on the TB is different you also need a short adaptor cable with 3 wires.

Looking at the Fiat workshop data, there are three connections to the TB (L062):

Pin 1 on TB PWM control signal Grey/Black Wire
Pin 2 on TB Ground Blue/Grey Wire
Pin 3 on TB +12 Volts Brown/Green Wire

The PWM signal comes from the ECU (M010) Connector A, Pin 59. I would expect this to swing between near +12V and Ground. If you are testing without the TB connected, you may need to connect a pull-up or pull-down resistor to make it develop a signal, I suggest 1K.


Some TBs have a potentiometer connected to Pin 4 which sends position feedback (status) to the ECU, but I don't think this was used in the Fiat/Iveco application.

I suspect the TB may have a way of signalling faults back to the ECU, possibly by shorting out the PWM pin, but this is only a guess.

It's also possible that the P0638 code can be generated indirectly, from monitoring of other parameters. Again, this is only a guess.


I hope this information helps - good luck

Hi Anthony489, thanks for your valuable reply.
It is indeed the 3.0 litre Iveco engine.

Actually the workshop manual says pin 1 pwm, pin 2 power supply, pin 3 ground, and pin 4 position signal. ( I have the Fiat Ducato Course Online pdf that can be found online for free). This seems correct as the old unit from Wahler still 'wakes' up. I don't think switching the pins on the new unit would be a good idea...
Indeed the L062 connection only shows 3 pins, but my pdf is too blurry to make out which is which, only pin 1 is quite clearly connected to pin 59 on the EDC16 ECU. I probed the connector coming from the ECU and 2 is indeed +, 3 is -.

The position pin is not used but on my old TB it is still functioning (gives back a voltage between 0 - 5V). This is the reason I initially thought the new one didn't work. Turns out the position signal is not used so it's probably not connected on the Pierburg unit to reduce costs.

I assume the other pins are mapped the same. I only learned about the new adaptor cable this morning to I hope the other pins are mapped the same compared to the Wahler unit.

When trying to read the PWM signal with the scope I did not use a pullup/pulldown resistor. Rookie mistake! The 3.75DC I read is indeed too strange and is probably caused by not using a resistor.

Because the vehicle is not here at home I did bring both old and new units home to see if I could put a PWM signal on it. Although I don't know the exact frequency the ECU puts out...

Hi Again

I have done some "digging" on the internet. I think the adaptor cable you need is Pierburg 4.07360.49.0. This looks like it has 4 pins each end, with 3 populated (wired). It is also rather expensive for what it is !


It's NOT safe to assume that the pin numbers on the new Pierburg TB are the same as the old Wahler TB, even if the connectors are the same type and will physically mate together. You must have the adaptor cable.


I replaced a Wahler on a 2.3 engine (different shape TB to the 3.0) with an updated Marelli, and the pin numbers and the connector shapes were completely different.

I don't know the PWM frequency, my best guess is about 1 kHz.

Hi Anthony489,
This is the adaptor cable I ordered today. I'll wait until it arrives so I can probe the cable. I didn't consider this indeed. The connectors look exactly the same so I assumed it would just work...

Why would they change this, so they can charge you another 50€ and make the TB itself look cheaper?
I didn't go for the same Wahler part because the Pierburg design looks beter protected against water ingress... Now I'm not so sure I made the right call.

Thanks again!

nigelvan said:

Hi Anthony489,
This is the adaptor cable I ordered today. I'll wait until it arrives so I can probe the cable. I didn't consider this indeed. The connectors look exactly the same so I assumed it would just work...

Why would they change this, so they can charge you another 50€ and make the TB itself look cheaper?
I didn't go for the same Wahler part because the Pierburg design looks beter protected against water ingress... Now I'm not so sure I made the right call.

Thanks again!

Click to expand...

Presumably the manufacturers use different wiring to each other hnecet the neede for the adapter I can't see fiat want it to to add it without reason especially when they had to replace the parts in warranty out of there pocket

In the meantime I found the pin configuration of the Pierburg tb and it came alive. I couldn't get the PWM signal right so it switched to half open, probably the frequency isn't right.
The adaptor cable got shipped last night so with some luck it arrives before the weekend and I can try it.
Someone also suggested switching the pins in the existing connector on the wiring loom but I don't know if that's a good idea in terms of long term reliability.

Hi guys, an update:
The cable adaptor arrived Friday evening and I got to install it on Saturday.
I had some bad connection in the original connector due to the use of the probes of my multimeter but that was easily fixed.
Once everything was connected the fault code cleared and I made a test drive. Everything seems to work again.
The van still idles a bit rough at the start-up though. After a few minutes/revs it purrs nicely at 800 rpm or so. Anyhow I'm glad this is fixed.