VCDS fault code clearing

[n10n]

Great deep dive as usual @mmi !

Please clear and recheck the faults the EGR connector disconnected.

Just to highlight this is a very good suggestion. I mean they all are but I think this should be the first test - if the other DTC's don't come back during this test it points to a fault in the new EGR. And it is the new component in the equation after all, thus the most likely culprit.

 

[mmi]

Great deep dive as usual @mmi !



Just to highlight this is a very good suggestion. I mean they all are but I think this should be the first test - if the other DTC's don't come back during this test it points to a fault in the new EGR. And it is the new component in the equation after all, thus the most likely culprit.

Just edited the proposal to include a request to get a blockmap - connector unplugged - to see if it has any secondary effects.

 

[Hannu]

Excellent! Well, "to err is human". I'd say it's definitely worth to learn how to use and exploit VCDS - even though we are still struggling to pinpoint the issue.

Below now the updated data items to look into - both engine idling and engine not running.
GREEN = good data
RED = implausible values

(1)​

Charge air pressure sensor G31 is wired separately to the ECU​

View attachment 270184
I find a bit confusing the voltage values now - almost at zero. Is there something loading the circuit? Would expect to see voltages close to 1 Volt.

(2)​

Also accelerator pedal has it's own wiring between the pedal and the ECU​

View attachment 270185

​

(3)​

Circuit D141 in wiring diagram has the following sensors (common 5 Volts with all sensors)​

(possibly the "Reference voltage circuit B"??)

G212 Exhaust gas recirculation potentiometer​

View attachment 270190

Wondering if there is something loading the circuit as the voltages seen by ECU are so low.
View attachment 270188
Can you access and measure EGR connector (disconnected)
See the picture above:
- should get 5 Volts between pin 1 (red wire) and pin 3 (brown wire)
- should get 5 Volts between pin 1 (red wire) and chassis ground
- should have continuity from pin 3 (brown wire) to chassis ground

Please clear and recheck the faults the EGR connector disconnected.
Ideally would also like to get a blockmap to see if anything else is affected.

---

View attachment 270186

Wondering if there is missing ground (for this sensor??) as the voltage is close to the reference voltage (5V).

View attachment 270192

Can you access the fuel pressure sensor connector?
On disconnected connector
- should get 5 Volts between pin 3 (red wire) and pin 1
- should get 5 Volts between pin 3 (red wire) and chassis ground
- should have continuity from pin 1 (brown wire) to chassis ground.

Please clear and recheck the faults the connector disconnected.
Ideally would also like to get a blockmap to see if anything else is affected.

---

Attached also collected blockmap data - parallel two maps before the faults, and two maps at the fault.
RED = not good

Very confusing,
First block map 11.41hrs is with EGR value disconnected
Second block map 13.22hrs is with fuel sensor disconnected yet VCDS showed EGR pressure sensor?
both would clear and the original fault still present, although when retested the fuel pressure did not return even though still disconnected.
I have a cheap multimeter which automatically controls what it measures and when testing the battery shows 12.5 volt
However when testing the wire to the sensors measured in ohms
ERG
red / brown 1.1
red / earth 1.04
brown/ earth 7.4
Fuel sensor
red / brown 1.5
red/ earth 1.1
brown earth 7.4

 

[Hannu]

I find a bit confusing the voltage values now - almost at zero. Is there something loading the circuit? Would expect to see voltages close to 1 Volt.

So my thinking at the moment is that if something is "loading" the circuit, its unlikely to be TWO broken wires in a loom and more likely to be a sensor or connection ?
I'm not ofay with canbus wiring and did think at one point this afternoon that I should try testing each earth with the multimeter to the battery but that may send 12v up the line and do more harm than good.

 

[mmi]

First block map 11.41hrs is with EGR value disconnected
Second block map 13.22hrs is with fuel sensor disconnected

Did you make notes what additional fault codes were triggered?

with fuel sensor disconnected yet VCDS showed EGR pressure sensor?

Sorry, I don't understand?

a cheap multimeter which automatically controls what it measures and when testing the battery shows 12.5 volt

That's interesting kind of instrument. What does it show when testing a 1.5 Volt battery - Volts or ohms?

However when testing the wire to the sensors measured in ohms
ERG
red / brown 1.1
red / earth 1.04
brown/ earth 7.4
Fuel sensor
red / brown 1.5
red/ earth 1.1
brown earth 7.4

Well, possibly there was no voltage present and thus the multimeter selected to measure resistance (ohms).
However, the fuel pressure sender VCDS reports 4810 mV - as if sensor is seeing the 5V reference voltage.
Anyways, resistance measurement across live circuit can't be trusted - true 1.1 ohms between red and brown would indicate a short between the two, which contradicts the 4.8 Volts seen by fuel pressure sender.

The confusing part is why unplugging EGR connector doesn't change anything in the blockmap - is there a break in the wiring.

I believe you need to get a more traditional multimeter with manually selectable measurements - to trace the 5 Volt at each connector.

 

[n10n]

First block map 11.41hrs is with EGR value disconnected
Second block map 13.22hrs is with fuel sensor disconnected yet VCDS showed EGR pressure sensor?

There are no material differences between these two blockmaps, so testing with EGR plug disconnected didn't really change much. Good news is that the EGR is not causing all the mayhem - but the bad news is that it's something else and we don't know what.

Like @mmi mentioned, many of the sensors outputting weird values (G31, G79, G185) have an independent wiring to the ECU. In addition we have G212 showing too low voltage (pointing to a positive feed issue) and G247 showing too high voltage (pointing to a ground issue). Putting these together I see these possible causes:

• Powering / grounding issue to the ECU itself - as the ECU is delivering both the positive (eg D141) and negative (eg 283) rails to the sensors ECU powering could affect multiple sensors at once. However ECU reports healthy voltages through IDE00019 and IDE01834.
• Unexpectedly high load / short that pulls some of the ECU voltages down
• Major wiring issue affecting many circuits from ECU
• Cooked ECU

This is still a very wide range of possibilities and I don't see easy ways to narrow the issues down without some rather extensive multimeter work and having the full wiring diagram as a reference. Personally I think the major wiring problem as the lowest probability of the above because many of the sensors have an independent wiring. My next steps with the diagnosis would be pulling the e-box open, taking a look at the ECU connector and starting unplugging / measuring individual ECU pins and wires from thereof. This is fairly involved undertaking but I think that's what it will take to pinpoint the issue - I may be wrong but seems to me blockmaps will not be able to help much more.

 

[Robert]

I have a cheap multimeter which automatically controls what it measures and when testing the battery shows 12.5 volt
However when testing the wire to the sensors measured in ohms

That's interesting kind of instrument. What does it show when testing a 1.5 Volt battery - Volts or ohms?

I use this one

UNI-T UT123D Smart True RMS Multimeter Digital AC/DC Current Volt Ohm Cap Test | eBay

This product does not include batteries. â Data Hold. Product Introductionï¼.

www.ebay.co.uk

and it is surprisingly good quality and high accuracy.
Unfortunately I never used measurement AUTOSELECTION mode as I don't trust it.

 

[Hannu]

Did you make notes what additional fault codes were triggered?


Sorry, I don't understand?


That's interesting kind of instrument. What does it show when testing a 1.5 Volt battery - Volts or ohms?


Well, possibly there was no voltage present and thus the multimeter selected to measure resistance (ohms).
However, the fuel pressure sender VCDS reports 4810 mV - as if sensor is seeing the 5V reference voltage.
Anyways, resistance measurement across live circuit can't be trusted - true 1.1 ohms between red and brown would indicate a short between the two, which contradicts the 4.8 Volts seen by fuel pressure sender.

The confusing part is why unplugging EGR connector doesn't change anything in the blockmap - is there a break in the wiring.

I believe you need to get a more traditional multimeter with manually selectable measurements - to trace the 5 Volt at each connector.

No additional fault codes triggered

I'll try the fuel sensor again tomorrow, my heads spinning but I'm sure it triggered a different fault.

Multimeter on order

 

[Hannu]

There are no material differences between these two blockmaps, so testing with EGR plug disconnected didn't really change much. Good news is that the EGR is not causing all the mayhem - but the bad news is that it's something else and we don't know what.

Like @mmi mentioned, many of the sensors outputting weird values (G31, G79, G185) have an independent wiring to the ECU. In addition we have G212 showing too low voltage (pointing to a positive feed issue) and G247 showing too high voltage (pointing to a ground issue). Putting these together I see these possible causes:

• Powering / grounding issue to the ECU itself - as the ECU is delivering both the positive (eg D141) and negative (eg 283) rails to the sensors ECU powering could affect multiple sensors at once. However ECU reports healthy voltages through IDE00019 and IDE01834.
• Unexpectedly high load / short that pulls some of the ECU voltages down
• Major wiring issue affecting many circuits from ECU
• Cooked ECU

This is still a very wide range of possibilities and I don't see easy ways to narrow the issues down without some rather extensive multimeter work and having the full wiring diagram as a reference. Personally I think the major wiring problem as the lowest probability of the above because many of the sensors have an independent wiring. My next steps with the diagnosis would be pulling the e-box open, taking a look at the ECU connector and starting unplugging / measuring individual ECU pins and wires from thereof. This is fairly involved undertaking but I think that's what it will take to pinpoint the issue - I may be wrong but seems to me blockmaps will not be able to help much more.

Sadly I think this is were my talent may prove lacking, I've convinced myself its something I've touched whilst replacing the EGR. I'm going to start by cleaning the chassis earths and the connections I have had off. Also double checking the block maps and faults when disconnecting the sensors

 

[Hannu]

Did you make notes what additional fault codes were triggered?


Sorry, I don't understand?


That's interesting kind of instrument. What does it show when testing a 1.5 Volt battery - Volts or ohms?


Well, possibly there was no voltage present and thus the multimeter selected to measure resistance (ohms).
However, the fuel pressure sender VCDS reports 4810 mV - as if sensor is seeing the 5V reference voltage.
Anyways, resistance measurement across live circuit can't be trusted - true 1.1 ohms between red and brown would indicate a short between the two, which contradicts the 4.8 Volts seen by fuel pressure sender.

The confusing part is why unplugging EGR connector doesn't change anything in the blockmap - is there a break in the wiring.

I believe you need to get a more traditional multimeter with manually selectable measurements - to trace the 5 Volt at each connector.

Only managed a couple of hours today but was able to obtain a better multimeter.
Removed both chassis earths on the N/S front chassis, cleaned and refitted.
Removed and tested the following:-
Fuel pressure sensor:- No voltage red to brown or red to earth, continuity between brown and earth. Carried out a fault test which did not show any fault with the sensor disconnected.
EGR Value:- No voltage red to brown or red to earth, continuity between brown and earth. Carried out fault test which showed the fault (first on the log)
Bear in mind that the fuel sensor remined discounted throughout the rest of the test. and the faults cleared following each test.
Engine Coolant Temp Sensor:- didn't test for voltage but was surprised to see the EGR flash up as a fault again ?
Coolant Pump 2:- didn't test for voltage but showed up as a fault
Intake Air Temp. Sensor:- didn't test for voltage but showed up as a fault.
I did a block map test following each test, attached.
I'm now of the opinion that the fault lay on circuit D141 but need a wiring diagram as to were the circuit starts and in which order the sensors are in the chain so I can see how far down the line the voltage goes. Or is that too simple?

 

[n10n]

I'm now of the opinion that the fault lay on circuit D141 but need a wiring diagram as to were the circuit starts and in which order the sensors are in the chain so I can see how far down the line the voltage goes.

This was CFCA engine, right? See T6 - 2.0 Diesel EU5 Engine Wiring Diagram - Download button on top right of the page.

D141 connects to ECU 60-pin connector pin 25 (section 7, page 158 / 8). You cannot discern the sensor chaining order from wiring diagrams.

 

[Hannu]

This was CFCA engine, right? See T6 - 2.0 Diesel EU5 Engine Wiring Diagram - Download button on top right of the page.

D141 connects to ECU 60-pin connector pin 25 (section 7, page 158 / 8). You cannot discern the sensor chaining order from wiring diagrams.

I would imagine its fused somewhere along the line and not straight into the ECU

 

[n10n]

I would imagine its fused somewhere along the line and not straight into the ECU

No. It’s only fused on the supply to ECU side.

Even high power circuits such as headlights connect directly to their control unit. Modern control units are made to withstand shorts on consumer side (and limit current, I presume, in order to protect wiring) so fusing is not needed.

 

[mmi]

This was CFCA engine, right? See T6 - 2.0 Diesel EU5 Engine Wiring Diagram - Download button on top right of the page.

Just a note to @Hannu - actually there are two wiring diagrams for CFCA depending on build date.
Direct link to the correct version https://www.t6forum.com/downloads/2-0-diesel-eu5-engine-wiring-diagram.230/version/307/download
Also can be found under downloads history tab (release 9 Jul 2021)

 

[mmi]

Intake Air Temp. Sensor:- didn't test for voltage but showed up as a fault.

Well, not important but I think this blockmap is missing - can't see any change in related data - on the maps it still was +1..+2 °C. Would have expected to show something like -40 °C.

---

My next steps with the diagnosis would be pulling the e-box open, taking a look at the ECU connector and starting unplugging / measuring individual ECU pins and wires from thereof.

Perhaps one last step before entering the e-box.

Just to rule out the sensors themselves by unplugging all the sensors (mentioned in post #17)

(3) Circuit D141 in wiring diagram has the following sensors (common 5 Volts with all sensors)​

G28 Engine speed sender​

G69 Throttle valve potentiometer​

G212 Exhaust gas recirculation potentiometer​

G247 Fuel pressure sender​

G584 Regulating flap potentiometer (turbo actuator)​

Then ignition on to verify if the +5 Volts miraculously springs up to (any) of the open plugs of (3). If that happens then by plugging back one at a time to find the offender.

 

[n10n]

Meanwhile, you might want to start drafting a list of stuff needed for working with VW connectors and typical wiring fixes - it’s a bit of a bummer if you open the e-box and don’t have something basic available to complete the job.

I’m not suggesting you order all of this but just to set the stage and prepare for what would possibly be needed here’s examples of some that I’ve found useful:

• ESSENTIAL: Terminal depinning tool kit - you might have to have ECU powered but pull individual pins away from connector for testing. You need depinning tools to do that: https://www.amazon.co.uk/Terminal-Removal-Extractor-Electrical-Connector/dp/B08LQG4YHN
• Jumper cables come in handy when you need to have ignition on / start the car but battery can’t be in situ as e-box is open: Amazon.co.uk
• Some generic tools - small side cutters and a stanley knife will get you far: Amazon.co.uk
• Soldering iron for patching broken wires. Any cheap one will do for very occasional work: Amazon.co.uk
• Some wire for the patches and during testing you might need to run bypass wires from little bit further. This is tricky one as there’s lot’s of wire gauges used but 16AWG (1mm^2) is a good compromise that will fit many uses: Amazon.co.uk
• Heat shrink tube with glue for protecting soldered joints: Amazon.co.uk
• Some electrical tape for fixing the looms that might need to be teared open. For engine bay waterproof and heat resistant type should be used. Not sure if this is good quality but something like this - and especially avoid typical cloth harness tape in engine bay: Amazon.co.uk
• Maybe couple of repair wires if some connector pins are corroded or break in opening. There are few types, I think this one is the most common (these can also be bought from the dealer for better quality and much higher price): https://www.amazon.co.uk/ECSiNG-Replacement-000979133E-Compatible-Accessories/dp/B0CDC1LJ4M

 

[n10n]

Some electrical tape for fixing the looms that might need to be teared open. For engine bay waterproof and heat resistant type should be used. Not sure if this is good quality but something like this - and especially avoid typical cloth harness tape in engine bay: Amazon.co.uk

Just a side note, this is the tape I use for looms exposed to elements and in engine bay, good stuff - unfortunately this does not seem to be available amazon.uk or even amazon.de at this time and that's why I didn't find it earlier: https://www.amazon.de/-/en/Coroplast-Thin-Fabric-Engine-Compartment/dp/B082DG4WR1

 

[n10n]

There are few types, I think this one is the most common (these can also be bought from the dealer for better quality and much higher price): https://www.amazon.co.uk/ECSiNG-Replacement-000979133E-Compatible-Accessories/dp/B0CDC1LJ4M

Scratch that. Apparently (still trying to 100% confirm for T6) ECU 60 pin connector terminal types are

000979030E small ones, 0,63mm, wire 0,5mm2
000979246E big ones, 1,5mm, wire 1,5mm2

For those, ready crimped repair wires do not seem to be available from Amazon. Terminals are though.

 

[Hannu]

Well, not important but I think this blockmap is missing - can't see any change in related data - on the maps it still was +1..+2 °C. Would have expected to show something like -40 °C.

---

Perhaps one last step before entering the e-box.

Just to rule out the sensors themselves by unplugging all the sensors (mentioned in post #17)

(3) Circuit D141 in wiring diagram has the following sensors (common 5 Volts with all sensors)​

G28 Engine speed sender​

G69 Throttle valve potentiometer​

G212 Exhaust gas recirculation potentiometer​

G247 Fuel pressure sender​

G584 Regulating flap potentiometer (turbo actuator)​

Then ignition on to verify if the +5 Volts miraculously springs up to (any) of the open plugs of (3). If that happens then by plugging back one at a time to find the offender.

Had a break from working on the van due to the weather but today thought I just disconnect the sensors to see if it made a difference, It didn't.
unfortunately, what I thought was the speed sensor turned out to be a reverse sensor.
Could anyone tell me were to fine the G28 Engine speed sender ¯\_(ツ)_/¯

 

[mmi]

Workshop manual states:

Engine speed sender - G28-​

Fitting location beneath oil filter bracket.​

​

​

#4 below​

​