Do I have conclusive evidence

see attahced uploads

Hi Avdr

Do you have any progress with your fault finding ?

I have looked at your latest waveform capture and it's hard to say anything about it when I´m not 100% sure how the system are operating.

One thing I would like to know - is there three or four wire going to the throttle body actuator ?

This picture is taken from a Fiat Ducato 2.3 JTD ( 2006 model ) and there is only three wires going to the throttle body actuator.

L062 = Throttle Body Actuator

Pin 3 = Ground Ref
Pin 2 = Power supply 12 Volt
Pin 1 = PWM Signal



Regards
Kim

Its 4 wire Kim. I found the same diagram as you have, which doesn't seem to have a feedback circuit on the earlier layout.

No further progress really. I'm still at war with my local Fiat agent who sold the part to me - they are very unco-operative. I'm 99% sure the fault lies in the throttle body, but that 1% doubt is telling me not to rule out an ECU fault, and to try and be 100% before I spend out for another throttle body.

The latest uploads showing the PWM signal but no current are strange. Im wondering if this is a result of a component failure in the throttle body - ie. a bad transistor, so we see the PWM signal but no current can flow. Or is it the ECU somehow shutting off the current but maintaining the PWM.
I can't find much (any) really useful technical info.
Andy

Hi Andy

Maybe this document could help.

I know that this information does not cover Fiat Ducato 2.3 JTD throttle body actuator but I reckon that the difference between manufacturs are small and so it might be usefull in your search for a solution on your problem.

It's from a Audi A4 2.0 TDI with engine type (BRE) and it in italian so you has to translate it.



Regards
Kim

Andy,
Is the dropout that you are referring-to the PWM line (blue trace in your logs above) when it goes to a duty cycle that is not 0% ?
I am not sure that there is necessarily a problem with these traces. What is quite common for this type of motor control is for a 0% or 100% duty cycle to be applied for a brief period on KOEO, before a range-limited duty-cycle is applied (for example a limited range of 5% to 95%). Is your symptom just not just an open-loop mapped duty-cycle being switched from one level to another? Or am I missing something here?
I have been following this thread for a couple of days, I am not sure that the throttle is your problem. The currents (presumably on the drive-side of the throttle) seem remarkably flat for something with a spring bias, but other than that....

Hi, Valhalla.

I don't think the dropout (when the PWM goes to ground, and stays low for some time) is normal, becuase this only happens when the fault code is cycling between stored and present.
Normally the PWM is stable indeffinitely (typically at 5% for idle once upto temp) and the drop out doesn't occur.

In live data, the only time I've seen a 0% duty command is again when the fault is cycling between present and stored.
Under normal operation the duty cycle in live data matches the duty cycle measured with pico.

There is a consistant issue with the valve, with P0638 being stored again within 10miles of clearing it. The main drawback - from a diagnostic angle atleast - is that its quite difficult to actually catch it in the act of playing up, often the P0638 will set out on the road, then by the time I'm back at the workshop it remains stored only, and valve functioning is back to normal.

I experimented with unplugging different wires to the valve, using the pico break out leads. If I unplug the PWM wire
while the van is at idle I get P0638 - Open circuit
Rather than the fault I've got at the moment, which is P0638 - Short to ground, this can be simulated by unplugging the feed to the valve instead (and leaving PWM connected).
It this short to ground that further re-enforces my feeling that the periods when PWM goes low and stays low is part of the faults nature.

RE: Currents, I find it odd how in the first set of traces I uploaded with current are so different to the second set.

Thanks

Hi Avdr

Did you read this line in the document ?

Here on italian.
In caso di grave guasto meccanico dell’attuatore, il pin 4 viene ciclicamente messo a massa a periodi della durata di circa 1 Sec.

Here on english.
In case of serious mechanical failure of the actuator, pin 4 is grounded in cyclically periods lasting about 1 Sec

Regards
Kim

Hi Kim, Yes I read the whole thing. In the case of the audi part, it is the feedback signal that is being grounded. In my case its the PWM. Could indeed be a similar stratergy though

I bought the Iveco part yesterday for the van, this is (I am told) a backward compatible part with the Fiat system. The Iveco throttle body is of a different design, and does indeed use only 3 wires - meaning you must also buy a short wiring harness adaptor. The feedback circuit is not utilised.
Planning to fit it tomorrow, will let you know how it goes.

Andy

Valve is fitted and all working well. Have driven over 50 miles personally in the van over the weekend, (easily enough to get a stored code prior to the new valve). ECU doesn't seem the least bit bothered about there no longer being a feedback circuit.

Feeling quite pleased with the outcome so far, just need to try and get my money back from Fiat