Skoda Octavia 2,0 TDI CR 2011 CFHC P0641 - Fixed

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Skoda Octavia 2,0 TDI CR 2011 CFHC P0641 - Fixed

Postby Martinjensen » Fri Apr 07, 2017 11:08 am

Hello

I have this Skoda Octavia 2,0 TDI CR 2001 CFHC that randomly sets 4123 - Sensor Reference Voltage A
P0641 00 [044]

The problem is that i cannot get the car to act up.

I have connected my 4 channel Pico to the 5V feed to: CMP, MAP, DPFE sensor, and EGR, CKP, RPS, Trottle body, and Turbo position sensor ( They are externalley connected)

I have been driving the car for 2 days now, but nothing happens.

Is there anyone that knows what components that uses Sensor Reference Voltage A ?

Regards Martin
Last edited by Martinjensen on Wed May 03, 2017 10:02 am, edited 5 times in total.
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Re: Skoda Octavia 2,0 TDI CR 2011 CFHC P0641

Postby Martinjensen » Fri Apr 07, 2017 5:29 pm

The car finaly acted up :-)

The feed for the camshaft position sensor (Blue trace) and the feed for the DPFE sensor (Yellow trace) shows a dip in voltage, and afterwards exessive noice on the yellow trace. (And the fault code was set again)

So now i know that is is not the MAP, EGR, CKP, RPS, Trottle body, or Turbo position sensor. :-)

This is giving me at least 2 channels i can use for further testing.

I would like to prove if it is the CMP or the DPFE sensor that is shorting out, or if there is a problem with the wiring or the ECU, ect ect...

Im thinking of adding an amp clamp to the feed of the 2 sensors, to prove whats wrong.
Are there any other measurements i can perform, so i am ready when the fault reoccurs?
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Re: Skoda Octavia 2,0 TDI CR 2001 CFHC P0641

Postby FioranoCars » Fri Apr 07, 2017 9:38 pm

Hi Martin
A few things, just IMHO
1. The noise is probably from over sampling, try lowering the current setting of 1MS to say 40ks (10k per channel per buffer = 100 samples per second), which should be more than enough. We've had lots of issues from excessive noise on high sample rates. Also try running the laptop on batteries rather than it's main power supply, again lots of issues ... of course if it's a desktop don't pull the plug !! :D
2.With the 2 sensors suffering a drop in voltage (assuming you are taking readings at the sensors themselves) then the problem is between the voltage regulator (or it's supply of battery voltage/it's own earth) and the last common place both wires for these 2 sensors are fed. Any downstream short will not affect the upstream, unless it overloads the 5v regulator - so your goal of measuring AMP is good, just finding the right wires to clamp is going to be the big issue, but worse case you can methodically work through them all 1 by 1 ... laborious but possible. Another choice might be to monitor the earth or supply wires to the ECU to see if the dropout correlated to a significant surge in current on an earth wire or supply, but your very low instance of the fault might cause issues logistically with this? Anyway maybe something is there give some food for though?
3. Further checks
- earths - are they good? being a 5v circuit they'll be earthed via the ECU's earth, so only need to concern yourself with those, but no harm in checking the engine earth (best drone using cranking amps to highlight any issues there. Same with supplies to the ECU (relays for ignition services and fuses properly seated?) Clearly knowing any environmental related thigns when teh fault occurs (bumps, cornering, revs, usage of wipers etc etc, might highlight a path)
- all the ECU pins clean and seating well ... and no extra stray strands on cable in the back of the ECU conenctor? (or water!) etc
4. Other measurements
- Try to figure out what other circuits are supplied from the same regulator, most ECU use more than 1 these days, and see if all sensors that share are affected or not, this will be a clear divining rod for any evaluation
- Amps - as said above, either on the 5v output by the ECU, or at each sensor ... or the battery voltage in/earth out (current being equal on all parts of a circuit), but only if you can prove which of these deal with the 5v regulator and if not much else is on the same wiring ... I guess if the amps are enough to pull down the regualtor it's probably big enough to spot.

It seems to be showing as an ECU fault, but I'm a fair way off the car, and many other things can be the cause, but 5v regulator/circuits do go down ...

Sadly with a 2 day gap between faults, it might be a tough one to confirm ...

another route might be to de-pin the circuits and use a separate 5v supply (piggy back the ECU battery and earth) and measure this for amps to see if the internal 5v regulator still drops ?

HTH or at least provokes some ideas! Time for a glass of wine, so brain switching off ... or had it already!

Richard
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Re: Skoda Octavia 2,0 TDI CR 2001 CFHC P0641

Postby STC » Fri Apr 07, 2017 9:57 pm

Im thinking of adding an amp clamp to the feed of the 2 sensors, to prove whats wrong.


I Don't think an amp clamp is going to help you as those sensors use very little current, Not something I have tried so we may learn something. Drama with an unproved test is may or not waste lots of time

Are there any other measurements i can perform, so i am ready when the fault reoccurs?


Pull the ECU out and you should have continuity on between the 5v supply pins for Cam & DPF. Now look for continuity to every other pin of that ECU. That should enlighten you as to what is on Sensor Circuit A.

Then it will be a case of beating the components with a screwdriver handle and tug of war with the loom with a view to replicate that fault.

This fault is another "Flag Flying" or a Technician "Screaming" for more than 4 Channels in the automotive arena, if Pico are listening? :)

Hope that helps Martin.

Edit
Our posts crossed Richard. Yours was not there when I clicked "Reply" to construct mine. Enjoy the Vino, I might do 3 or 4 bottles. They take up too much space, well clutter really :)
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Re: Skoda Octavia 2,0 TDI CR 2001 CFHC P0641

Postby STC » Fri Apr 07, 2017 10:35 pm

Just for clarity Martin ?
Skoda Octavia 2,0 TDI CR 2001 CFHC P0641


A CFHC Engine Code, Model Year 2001 & "CR" Common Rail ?

Have I read something wrong here ? CFHC Engine will not be fitted to a 2001 VAG.
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Re: Skoda Octavia 2,0 TDI CR 2011 CFHC P0641

Postby Martinjensen » Sat Apr 08, 2017 8:25 am

Hello Richard and STC.

Thank you for answering, there are some great ideas, and i will set up some further tests, and get back with the results.

@ STC Sorry for the mistake with the model year of the car, its 2011. Well spottet :-)
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Re: Skoda Octavia 2,0 TDI CR 2011 CFHC P0641

Postby FioranoCars » Sat Apr 08, 2017 9:13 am

STC
The amp clamps will give an idea of the type of fault and location, if there is a high amp event during the failure moment, then you could use that to trace where the fault is, in that where on the 5v output line it shorts to earth (not the ecu return path), or if the sensor is indeed the earth short.

Monitoring amps has been used in few of the Pico write ups as a technique as well as either Frank Massey or James Dillon et al, so does have some value, but with a fault like this, the more options you have lined up the more chance you can use the one technique that suits your hunch or theory to confirm or disprove it.

As you know, STC, I'm a big fan of the HOOK and using amps, inrush and operating, along with volt drop, to pin point not just the symptoms but to confirm the root cause of any fault, so it's no surprise I see amp monitoring of the 5v outputs and returns as a good option. As most (I assume all but will leave the door open to be corrected! :D ) 5v sensor circuits use the ECU for their earth, to ensure a true 5v p-d (avoiding any engine earth volt drop or noise issues), then the sum of output amps minus return amps should be ZERO, or thereabouts, with any significant deviation correlation at failure time indicating a short to different earth path. Well that's a theory, never put it to the test, so could be way off the mark. But would show a wiring earth short, or internal sensor short to ground fault.

The or well at least my thinking/theory behind this is the sensor can't be earthed to the engine, it must float to the earth supplied, otherwise the whole point of having a 5v stable and regulated accurate voltage level would be compromised by any issue of the engine being a small say 0.15v above battery earth, and with cranking or high alternator output during headlight or heater operation this short of figure would be common, and enough to upset most sensors ... Maybe some one out there has a technical document or other further reading on this point? Not seen anything specifically written so would be interested to know if there is anything.

HTH

Richard
Ps
STC, Did you sort the door lock issues? If you want to share, then go for a new thread... Or drop me a pm / call...
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Re: Skoda Octavia 2,0 TDI CR 2011 CFHC P0641

Postby STC » Sat Apr 08, 2017 10:11 am

Richard
The door lock is sorted but a case study in itself and worthy of a new thread that i will put together.
Here we digress. So back to Martin and the Passatt. An interesting one where I am keen to learn the outcome.
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Re: Skoda Octavia 2,0 TDI CR 2011 CFHC P0641

Postby STC » Sat Apr 08, 2017 10:35 am

I cannot see the amp clamp revealing any more than Martin has already established.

For sure the Mosfet or its control has gone wonkey within the Ecu or it is being pulled down externally in the wiring or a component.

All futher testing now is futile regardless of whatever Super Dooper Carlos Fandago gadget he attaches to the scope.

He has a fault in SENSOR CIRCUIT A

He is asking what is populated on said Circuit A so he can target his detective skills in the applicable vicinity.

Armed with that information he could, theoratically find the fault with a 5v bulb. The scope has worked wonders proving / verifying the fault code.


I maintain that he needs to verify all the connected pins on that Ecu to establish Circuit A in its entirety so he can move forwards.
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Re: Skoda Octavia 2,0 TDI CR 2011 CFHC P0641

Postby FioranoCars » Sat Apr 08, 2017 11:06 am

STC wrote:I cannot see the amp clamp revealing any more


Precisely, and tongue in cheek, I'm saying to you as I did on the Phone, AMPS is a very good way to pinpoint the fault, or more precisely which of the lines in this instance might be overloading the "sensor A" circuit, which feeds probably 1/2 or 1/3 of all the 5v sensors, depending on how many regulators that ECU has. Replacing the ECU on the basis of what we know so far is another spitting bits/replacing the symptom, the root cause must be found and repaired, then the ECU can be checked for long term damage (OK, it might turn out to be the ECU, but we don't know that yet for sure, and we'd be better proving the sensor circuits are not part of the problem before replacing a potentially good component ... dare I mention door locks?! :o :o ).

Take a deep breath, and realise that just because you have not had a light bulb moment with amps, and please throw away all your 5v bulbs away right now, that you should NOT stand in the way of others having it. AMPs are very useful for diagnostics, in fact essential in many instances, get your HOOK out and use it, then you might start to appreciate it.

Maybe the above should be a PM not public, but I'm guessing you know me well enough that it's meant to cajole you into getting on board with AMPs, and that if you are being a stick in the mud, then others out there need to have the lecture too !!! :D It's left as public on the basis of learning.

Lets take any more comments on this to a coffee and engine bay when you're passing next!

Have a sunny weekend

Best
Richard
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