Clutch Pedal Switch for Engine Start (F194) Fault

[evopilot]

Hi all,
Ive searched and searched the forums but have been unable to find a replicating problem such as mine and my car has been sitting for weeks now unable to start. Ill try an explain everything in a easy to read format and get to the point instead of spamming the thread

Original problem:
my clutch pedal had lost all pressure and the clutch could not engage. (lets call this clutch master cylinder/switch 1)

Solution:
Order a new clutch master switch and fit (LUK brand) (lets call this clutch master cylinder/switch 2)

At this point after the new switch was installed pressure was restored however the car would no longer start.

New Problem:
"Engine start system fault. Please contact workshop" error now displays on the screen when you press down the clutch pedal to start the car.

At this point in ran VCDS and i got "Clutch Pedal Switch for Engine Start (F194) Not A Plausible Signal" knowing that this new clutch pedal master cylinder and switch was brand new i went part to the car parts supplier and insisted it was faulty. The store gave me another one i cant recall the brand but looked almost identical including the reference numbers at the side of it. (lets call this clutch master cylinder/switch 3).

Clutch master cylinder/switch 3 is now installed with the system pressurized with all fault codes cleared by VCDS but again the error"Engine start system fault. Please contact workshop" remains even after this install.

I then made a decision to back track slightly and install the original Clutch master cylinder/switch 1 as i knew the electrics of this one were ok but it had faulty hydraulics and would not engage the clutch only to be horrified that even now reverting to the original faulty part the "Engine start system fault. Please contact workshop" warning is still there and wont clear.

Summary:
3 "faulty" clutch master cylinders/switches
Car wont start error
I can see on the data bits in channel 42 when i press and depress the clutch pedal the data bits change so the car can see the switch is there
Ive checked every fuse beside the steering wheel, in the boot and none are blown

Today i got a loan of a friends Snap-On SOLUS diagnostics tool hoping that would be in some way able to see more data but it was the exact same as VCDS in the fault information shown.

Has anybody ever seen a similar scenario like this or does the clutch master cylinder/switch need to be adapted to the car. Does anybody have wiring diagrams? is their a relay or something im missing beyond a fuse?

[Magnet]

Hello Andrew,

Thanks for being in touch with the forum, and sorry to hear of your issue. 
Many thanks also for the detailed description and action taken. The only thing that I’m not clear on is what you have done (with the clutch hydraulics) to rectify the primary loss of clutch pressure. I saw LUK and clutch, but on re-reading this, it seems the switch was by LUK rather than any clutch parts replacement. 
Kind regards,

Gareth.

p.s. Not wanting to be critical, but constructive, when I say, I think your location description might not be to your best advantage. As has been said on here so many times, we try to come over as being as helpful and friendly as we can, and I think that that would probably include advice on where best to seek assistance in your area, and even hands on support if that were possible. 

[beemerboy9]

54 minutes ago, Magnet said:

Hello Andrew,

TThe only thing that I’m not clear on is what you have done (with the clutch hydraulics) to rectify the primary loss of clutch pressure. I saw LUK and clutch, but on re-reading this, it seems the switch was by LUK rather than any clutch parts replacement. 
Kind regards,

Gareth.

 

The switch was attached to a new master cylinder .....?????

[Magnet]

Thanks John, but the common issue with loss of hydraulic pressure is often associated with slave cylinder assemblies, and not master cylinders. 
We shall have to wait until Andrew comes back to us. 
Kind regards,

Gareth. 

[evopilot]

2 hours ago, Magnet said:

Hello Andrew,

Thanks for being in touch with the forum, and sorry to hear of your issue. 
Many thanks also for the detailed description and action taken. The only thing that I’m not clear on is what you have done (with the clutch hydraulics) to rectify the primary loss of clutch pressure. I saw LUK and clutch, but on re-reading this, it seems the switch was by LUK rather than any clutch parts replacement. 
Kind regards,

Gareth.

p.s. Not wanting to be critical, but constructive, when I say, I think your location description might not be to your best advantage. As has been said on here so many times, we try to come over as being as helpful and friendly as we can, and I think that that would probably include advice on where best to seek assistance in your area, and even hands on support if that were possible. 

Hi Gareth,

To be clear the clutch itself although initially suspected of being an issue was not touched nor was the slave cylinder. How this initial diagnosis was made was was the cars clutch bite point was very low..... as in you would have to press the pedal 80-90% down before it would engage. If the pedal was pumped constantly the pressure would improve (to say  only needing to have the clutch pedal pressed 30% before it would engage) when the car had warmed up after a few miles/kilometers. A fluid swap was done with fresh dot 4 at the same time clutch master cylinder/switch 2 was installed.

Naturally after each install mentioned in the original post the the clutch would also need to be bled too.

After each install the car would feel much improved in regards to bite points and how the clutch felt similar to when the car was first purchased in 2019 although the electrical system is now not happy 😕

*noting your point about the location in my bio*

Thanks

[evopilot]

1 hour ago, beemerboy9 said:

The switch was attached to a new master cylinder .....?????

Yup unfortunatly in this model the switch is non removable and built into the master cylinder similar to this picture:

[Stevey Y]

5 hours ago, evopilot said:

Yup unfortunatly in this model the switch is non removable and built into the master cylinder similar to this picture:

Hi there is another switch activated when the pedal is pushed down it is a large blue coil with a black top that bends at an angle when the pedal is depressed and it is attached to its own separate casting on the pedal I am pretty sure that is the make/break switch for the engine start system, they are a curse inherited from automatics and in the good old days of overhead mounted plunger switches you could bridge the terminals on the switch and it would allow you to start, I have the same problem with my clutch master cylinder and suspect I will have to change the other switch when I renew the cylinder.

Steve.

[Stevey Y]

Hi alternatively take the connector off of the master cylinder and bridge the terminals and see if that works, I am trying to find out if the master cylinder needs re coding.

Steve.

[evopilot]

2 hours ago, Stevey Y said:

Hi there is another switch activated when the pedal is pushed down it is a large blue coil with a black top that bends at an angle when the pedal is depressed and it is attached to its own separate casting on the pedal I am pretty sure that is the make/break switch for the engine start system, they are a curse inherited from automatics and in the good old days of overhead mounted plunger switches you could bridge the terminals on the switch and it would allow you to start, I have the same problem with my clutch master cylinder and suspect I will have to change the other switch when I renew the cylinder.

Steve.

The only coil that is present is a large spring that gives the pedal itself the tension i cant see other switch's in the vicinity other then the brake pedal switch which is different 😞

[evopilot]

1 hour ago, Stevey Y said:

Hi alternatively take the connector off of the master cylinder and bridge the terminals and see if that works, I am trying to find out if the master cylinder needs re coding.

Steve.

Ive thought about trying similar but the master cylinder has 6 connectors unlikey the older ones that have two 😞

 

[Stevey Y]

17 hours ago, evopilot said:

Ive thought about trying similar but the master cylinder has 6 connectors unlikey the older ones that have two 😞

 

Hi I see what you mean its all wired in on the electromechanical braking system, I am trying to get hold  of my garage to get the number for the Audi moonlighting engineer they use but they are not open until Monday, I have a very strong interest in getting round this problem as my car is due for a master cylinder change and I don't want to get into the same situation, I am leaning more towards readaptation but feel it may be worth looking at the fuses, believe me as soon as I can get an honest informed opinion I will gladly pass you the information.

Steve.

[evopilot]

 

OK so spent a good bit of time at this yesterday and even tried a new clutch position sensor (clutch master cylinder/switch 4) and im happy now the problem is not the sensor it can not be as the problem is following even the brand new sensors installed.... (side note if anybody is looking for a sensor i have a few spare for sale lol)

Also to rule it out i even tried a hail Mary and purchased and fitted a brand new main battery, the thought behind this was sometime the engine would throw a fault for implausible starter signal which i read could be a symptom of a tired battery. so seen as the battery is 6/7yrs old now i installed a new one.

 

So yesterdays testing:

First off a continuity test between the connector that would connect directly onto the clutch sensor and the end point i could trace, the purpose of this testing was to try identify a severed/loose wire etc

1. Brown wire (Main earth for switch) checked and OK, also spliced the cable and created a new earth of my own to double check and that was OK too

2. Green/Grey wire (connection to Main ECU) checked and OK to 17pin coupler, checked and OK to exit wire leaving coupler and checked at pin 89 on main ECU all OK.

3. Blue/Grey wire (Park/Neutral to main harness) checked between plug and further up the cable unsure of actual end point of this wire.

4. Black/Blue wire (To fuse 2 & 4 fuse holder F) I could not tell where fuse holder F was or identify it correctly so continuity could not be verified. However their is voltage on the wire but more on that later.

5. Green/Yellow wire (Parking brake control unit connection) continuity unchecked as the error does not seen to be related and their is voltage on the wire but more on that later too.

6. Red/Blue (To fuse box drivers side doorway) continuity is OK entering and exiting the fuse

 

Voltage at the connector:

This test was done using a chassis ground/earth and by using pin 1 below for double checking

1. Brown wire (Main earth for switch) voltage not expected as earth wire and 0 volts found, satisfied earth is good due to above.

2. Green/Grey wire (connection to Main ECU) zero voltage found

3. Blue/Grey wire (Park/Neutral to main harness) 6.8v found

4. Black/Blue wire (To fuse 2 & 4 fuse holder F) 11.8v found

5. Green/Yellow wire (Parking brake control unit connection) 10.1v found

6. Red/Blue (To fuse box drivers side doorway) 11.8v found

It would really help if i had some verification of what the voltages etc should be with the clutch pressed and depressed so if anybody could assist me on that i would be ever so grateful.

 

Additional checks:

Also i read online that connection wire 3 directly to earth on the loom side not coming form the sensor is a method to trick the ecu in thinking the pedal was depressed however i can confirm this does not work. Actually if wire 3 is snipped the clutch pedal operates correctly to a point and throws zero fault codes but the ecu has no way of knowing you have actually pressed the pedal in. If you earth it as mentioned above the fault trips immediately and we are back to square one. I am worried about this slightly as i see voltage on that wire now (earth test was done prior to voltage test BTW) so by the main harness sending 6.8v down this wire to the connector and i earth it that would naturally cause a fault or trip a fuse i would have thought but no fuses were tripped.

Also i gained access to the convenience control ecu down the back and checked that for loose wires but all seemed ok

Apologies for the long winded reply but i hope Ive broken it down into readable chunks and either somebody can help me or one day somebody on the web finds this in a search and it helps them hopefully by then my issue is resolved.

 

Closing questions:

Does anybody know the voltages i should be seeing or the voltages the car should be expecting etc?

Should their be voltage on wire 2?

Should their be voltage on wire 3?

Where is fuse holder F according to audi?

[evopilot]

Alternative but expensive options which id rather not do due to the cost and no guarantee of helping would include, purchasing a new convenience control ecu, installing a new wiring loom or new main ecu

My gut is telling me wiring loom issue and their seems to be allot of people breaking manual versions like mine so that might be an option but hopefully i can get a section of it and and the full car loom doesn't need to be purchased:

 

 

Hopefully however somebody know the voltage specs on the sensor etc before i go down that road

[Stevey Y]

13 minutes ago, evopilot said:

Alternative but expensive options which id rather not do due to the cost and no guarantee of helping would include, purchasing a new convenience control ecu, installing a new wiring loom or new main ecu

My gut is telling me wiring loom issue and their seems to be allot of people breaking manual versions like mine so that might be an option but hopefully i can get a section of it and and the full car loom doesn't need to be purchased:

 

 

Hopefully however somebody know the voltage specs on the sensor etc before i go down that road

Hi Andrew I have today managed to try Vagcom on my car and there does not seem to be any readaptation for the switch also have done a fair amount of reading on American sites which only really mention the stop/start control module which I realise is not much help but looking at what you have done I will try to see if I can get any voltage specs Tuesday when my car goes in for the same. my new clutch is slipping and on the inspection Friday he also noticed I have an almighty oily grunge leak which I think is a turbo hose and the gearbox mount is past its best all JOY. And work has gone mad so I see where you are coming from.

Steve.

[evopilot]

On 1/23/2022 at 4:26 PM, Stevey Y said:

Hi Andrew I have today managed to try Vagcom on my car and there does not seem to be any readaptation for the switch also have done a fair amount of reading on American sites which only really mention the stop/start control module which I realise is not much help but looking at what you have done I will try to see if I can get any voltage specs Tuesday when my car goes in for the same. my new clutch is slipping and on the inspection Friday he also noticed I have an almighty oily grunge leak which I think is a turbo hose and the gearbox mount is past its best all JOY. And work has gone mad so I see where you are coming from.

Steve.

if you could get your hands on the voltage specs id be forever grateful mate

 

Also side note ive ordered a new connector block a wiring from Audi, should be here Wednesday to try rule out the connector block itself

[Stevey Y]

21 hours ago, evopilot said:

if you could get your hands on the voltage specs id be forever grateful mate

 

Also side note ive ordered a new connector block a wiring from Audi, should be here Wednesday to try rule out the connector block itself

Hi Andrew, I got my master cylinder done today and as per the engineers instructions there is a definite sequence to observed before bleeding it out, to my method I would have just fitted it, bled it, and then tried to start the car, wrong according to our instructions, before you bleed the unit out you must leave the pedal on the floor and then start the car run it for a couple of min then turn it off and bleed it out, looking at it logically think that by the pedal being at the furthest point of travel the sensor at the top of the cylinder registers itself electromagnetically like a Hall sensor and despite my mate snapping the sensor mounting, we had to re mount it and fix it on with cable ties but it still works until I get another cylinder.

I have asked the engineer if he can get the voltages for the diagram supplied, he says its not his speciality but he will ask the electrician where he works to look and advise on voltages, to my mind the control unit is blocking the introduction of the new unit as you described you can see the data bits change but its not allowing the the cylinder to register to start the vehicle, I don't honestly think its a wiring problem but it won't hurt to try another piece of loom, I could well be wrong and that solves the problem, also before fitting the new unit we deleted any codes that were present, back to you in a couple of days,  it was the master cylinder not releasing the pressure that was causing my clutch to slip, why are these cars so complex.

Steve.

[evopilot]

So connector from the loom replaced today with a fresh connector block and wiring, unfortunately its the same fault

Audi advised today to use a genuine clutch master cylinder/switch on this make/model of car

 

That leaves:

Replace convenience ECU in boot as that is the component whats throwing the error (a long shot and not overly expensive)

Replace engine bay loom section (most expensive of all options)

Replace main ecu (bit of a hail mary this option and not sure on cost of ecu)

Replace clutch master cylinder/switch with genuine one (this will be the 5th sensor/switch if i buy this... madness)

[Stevey Y]

17 hours ago, evopilot said:

So connector from the loom replaced today with a fresh connector block and wiring, unfortunately its the same fault

Audi advised today to use a genuine clutch master cylinder/switch on this make/model of car

 

That leaves:

Replace convenience ECU in boot as that is the component whats throwing the error (a long shot and not overly expensive)

Replace engine bay loom section (most expensive of all options)

Replace main ecu (bit of a hail mary this option and not sure on cost of ecu)

Replace clutch master cylinder/switch with genuine one (this will be the 5th sensor/switch if i buy this... madness)

Hi Andrew, I have not heard anything from the techno twins about voltages but in saying that I had a run down to our local German car specialists today so while down there I picked one of the engineers brains, he said that he concurred with my theory that the switch on the cylinder was not able to communicate with the control unit and if you have already fitted an LUK unit which is O.E. and thats not worked its a problem at the other end in the control unit, he then went on to say they had problems before with CCM units in A6 late models as due to moisture ingression the terminals in the plugs had corrode and in one case the wiring to the plugs had become brittle and the plastic covering on the wires was crusty and failing, its worth looking, I am assuming you have the saloon model and if you can get the wiring diagram and position of the module I would be looking at that before I would spend any money on looms/ecus or master cylinders, I will start pestering the other two tomorrow for the voltage stats, but I have a strong feeling that the ECU in the boot is the culprit.

Steve.

 

[evopilot]

man i cant thank you enough for asking these guy the questions you have already, its much aprecaited.

ive pulled up the flow chart for the convenience ecu, so tomorrow after work ill have a look were ive marked the red x and see what condition that wire is in and voltage etc maybe test for continuity, this is the wire i wasn't sure should have 6.8v on it after reading online to simply earth this connection to "trick" the ecu into thinking the pedal was pushed in

[Stevey Y]

18 hours ago, evopilot said:

man i cant thank you enough for asking these guy the questions you have already, its much aprecaited.

ive pulled up the flow chart for the convenience ecu, so tomorrow after work ill have a look were ive marked the red x and see what condition that wire is in and voltage etc maybe test for continuity, this is the wire i wasn't sure should have 6.8v on it after reading online to simply earth this connection to "trick" the ecu into thinking the pedal was pushed in

Hi I saw the same guy today as I had to take the customer back to get his car, the engineer waved me down before I left and asked if there was any news subject to what he told me yesterday, I told him none but he went on to say its worth visual checking all the wiring in that area apparently when the wire corrode its a case of chase the ace to find the culprit, I also found another interesting fact that most dealerships have a machine that plugs into the OBD port that runs its own test voltages on the wiring system throws up a schematic of the offending section or module, this normally takes 15mins and they can have lunch in the 1: 3/4 hours thats chargable and fleece the customer for both the part/labour and diagnostics, this guy used to work for BMW so I have no reason to doubt him.

I do hope we can solve this problem as times personal effort you are overdue a result, as for talking to people this particular problem has gripped my resolve to find out what it actually is and by asking everybody and anybody who might know I learn things peripheral to the problem.

Steve.

[evopilot]

Small update but after installing ODIS and following the trouble shooting Ive narrowed down the issue, its a bit picture heavy but the below is the step by step of ODIS pointing out the ECU is not seeing the clutch pedal being pressed:

 

Ready to be tested:

 

Switch is being picked up as being pressed but the ecu/can cannot see the pedal being pressed

 

J623 and G476 testing to follow asap but at least im no longer throwing darts at the issue

 

 

[Stevey Y]

18 hours ago, evopilot said:

Small update but after installing ODIS and following the trouble shooting Ive narrowed down the issue, its a bit picture heavy but the below is the step by step of ODIS pointing out the ECU is not seeing the clutch pedal being pressed:

 

Ready to be tested:

 

Switch is being picked up as being pressed but the ecu/can cannot see the pedal being pressed

 

J623 and G476 testing to follow asap but at least im no longer throwing darts at the issue

 

 

Hi Andrew got this off an American website it may well be worth a look its a relay that is causing the problem although your car is a 15 plate it might be the relay if you read the blog, its for left hand drive but if you transpose the diagrams they are exactly what we have on our cars.

[evopilot]

Cheers Steve, have you a link to the original thread and ill check it out?

[Stevey Y]

On 2/17/2022 at 12:47 AM, evopilot said:

Cheers Steve, have you a link to the original thread and ill check it out?

Hi try these Andrew, the further you dig in on the NHTSA site the more appalling the list of TSBs become apparently unknown in Europe do you think they set out to supply the yanks with substandard models I think not, its clear the Krauts have been working on the theory if they don't tell us we can't moan.

[evopilot]

So an update.

Last week after a few weeks of searching i was able to source some genuine VAG diagnostics cables to work with ODIS

I picked up VAG 1598/42 and VAG 1598/39

This then allowed me today to check the signals being received by the ECU which narrowed it down to a fault on wire/pin 44 on the 94 pin side of the ecu, the ECU was seeing voltage permanently but this should have dropped to a earthed signal once the clutch was pressed in.

The culprit wire came out of the master cylinder on pin 3 then split into two parts.... one length went into the convenience module in the boot and the second branched off and went into the ecu at pin 44 as i mentioned above.

Pin pointing that the convenience module was getting the correct signal i was able to narrow down that the trouble was after the cable splits and went to the ecu.

I ran a fresh length of cable myself from the split to the ecu pin 44 and BINGO she fired up, gave the car the once over on ODIS and the error was fully gone.

Nearly six months of the car sitting up in my garage and shes back on the road

Edited April 24, 2022 by evopilot