06 Jetta TDI Clutch pedal switch/sensor?

Discussion in 'Mk5 VW Jetta, Sportwagen, and Audi A3 TDI forum' started by mirek07, Jan 22, 2012.

  1. mirek07

    mirek07 New Member

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    Car:
    2006 Jetta TDI
    Recently I have to press very hard on clutch pedal to start the engine on my 06 Jetta TDI. Any idea what could cost this problem? Thanks!
     
  2. chittychittybangbang

    chittychittybangbang Administrator

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    Car:
    2006 Jetta TDI
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    CT
    Only thing I can think of is bad clutch pedal switch. I don't know if it's on the top or bottom of pedal travel since I've never looked. I've never tried to jump the switch but I suppose it should be possible for testing purposes. For safety reasons, don't jump the switch for regular use.

    EDIT: It looks like they changed the switch type on the mk5 cars, see the next post
     
    Last edited by a moderator: Jan 24, 2012
  3. Ol'Rattler

    Ol'Rattler Well-Known Member

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    Car:
    06 TDI Jetta
    Location:
    Marysvile, WA.
    I know this one from my experience when I changed my clutch and had a similar problem. But first some education.

    With the introduction of CanBus the A5 work quite a bit differently than the A4's. There is no switch in the usual sense for the clutch. What there is is an electronic sensor mounted on the outside of the master cylinder, under the hood that detects the master cylinders piston movement and sends an "OK to start" signal to the ECU.

    Being that is a sensor and not a switch, it is sending a discrete signal to the ECU and trying to bypass the sensor probably won't make the car start and might even burn out the ECU in the process. My best guess is that the sensor works something like a Hall effect sensor.

    With my car, what was happening was the slave cylinder was reaching the end of it's travel before the master cylinder piston was in "proximity" of the sensor. Another words, the clutch petal wasn't close enough to the floor for the car to start.

    I found that If I pushed real hard, I was able to get the car to the start, but in the process, it overextended the slave, destroying it.

    Could you give more info on your car such as miles on the clutch, how suddenly this happened and anything else you can think of?

    At this point I would not think it is anything hydraulic. My best guess would be a loose slave cylinder, worn or damaged slave rod, a worn throw out bearing or a bent throw out bearing arm.

    Almost forgot the obvious. Is there something blocking the clutch petals movement like a floor mat or wiring?
     
    Last edited by a moderator: Jan 24, 2012
  4. mirek07

    mirek07 New Member

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    Car:
    2006 Jetta TDI
    This is 06 Jetta TDI 180000km clutch was changed in Oct. 2011 at 170000km.
    This problem start 2-3 weeks ago and getting worst. Car is still starting with hard pedal press
    and nothing is disturbing movement. The clutch itself fills and working perfect!
    Thanks for great education and all info!!!
     
  5. Ol'Rattler

    Ol'Rattler Well-Known Member

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    You could check the master by having someone hold the clutch petal down with normal force and open the bleeder briefly and then close it. If the master is OK, the petal should sink the rest of the way to the floor to the start position. Without releasing the clutch, see if the starter will engage now.

    Make sure they understand to hold the petal to the floor and not let up on it until the bleeder is closed.

    You might have air in the slave. Bleed the clutch system and see if that helps. When you bleed, don't let the level in the reservoir get more than about 1/4th of the way from the top or you will be introducing air into the system.

    Probably after that, you will have to remove the slave for further investigation............
     
  6. wasp

    wasp New Member

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    Car:
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    it can be safely bypassed by grounding a purple wire somewhere. real helpful, i know. i did it for a remote start install (compustar) on a 5 speed and it works perfect. if this is of interest i'll try to find the link where i found the info. i think it was on the golf mk5 forum
     
  7. mirek07

    mirek07 New Member

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    2006 Jetta TDI
    I will greatly appreciate if you can found it for me. Clutch is working perfect only trouble is starting.
    If I can bypassed this sensor I wouldn’t worry about it for now.
    :thumbsup
     
  8. Ol'Rattler

    Ol'Rattler Well-Known Member

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    06 TDI Jetta
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    I'd like a better understanding of how this works, as well. My concern with the start sensor permanently bypassed would be that the cruise wouldn't work and the ECU would always be receiving a signal that the clutch is disengaged causing possible drivability issues.

    I thought of bypassing the sensor when I had my clutch issues and decided the best option was to make the car operate as it was designed because of the issues I mentioned above.

    I would say that if you do bypass the interlock, use a momentary switch so that you bypass the sensor to start and when you release the switch, the ECU will be happy and let the CC operate normally and also not think the clutch is always pushed in.
     
    Last edited by a moderator: Feb 6, 2012
  9. csigona

    csigona New Member

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    Car:
    2002 Jetta TDI, 2005 Jetta TDI BRM
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    Newport, NY
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    This is an old thread, but I can add something useful. Like Ol'Rattler, after replacing clutch / flywheel, pressure plate / release bearing, I too ended up with a clutch pedal that wouldn't go down all the way and so the clutch position sensor did not inform the computer that the pedal was down and it was safe to power up the starter motor. When the pedal is pressed (not forced), there is still a space of about 1" before it's fully depressed, and just like Ol'Rattler says, if you force it, the pedal will travel that additional inch and the motor will start.

    I tried many things short of replacing the clutch set. I pulled out the transmission and reinserted it multiple times. I fiddled with the hydraulics, replaced the slave cylinder, bled and re-bled the line, but have not yet gotten to the bottom of the problem. I still need to figure it out, but until I do, I have bypassed the clutch pedal position sensor so I can use the car. The motor now starts (like cars used to) without pressing the clutch pedal, and the cruise control continues to work.

    I am no expert with this sensor, and would be happy to accept correction, but I think I know how it works. It is only one hall effect device, but, in effect, two switches. One switch (pins 2 and 5) says when the clutch pedal starts to move. This is used to turn off cruise control when you press the clutch. The other switch (pins 1 and 4) says when the clutch pedal reaches the end of its travel. Pin 1 (brown) is ground; pin 4 (purple/black) connects to pin 1 when the clutch pedal is fully depressed. By grounding pin 4, you make it that the clutch pedal is depressed for starting purposes, but not depressed for cruise control purposes. This is shown in diagram 46/15, page EWD-89 of the Bentley manual. The sensor is G476.

    To ground pin 4, disconnect the switch connector from the master clutch cylinder. Unwrap the electrical tape enough to see the wires. Pin 4 will go to a purple/black wire. Remove about 1/2" of insulation without breaking the wire, then take another piece of wire, the bypass wire, wrap one end around the exposed copper on the purple/black wire, and solder it. I covered the exposed wire with liquid electrical tape (black goop) to make it waterproof, then wrapped the wires back up with new electrical tape. Finally connect the other end of the bypass wire to ground. The battery's negative terminal is nearby, so you have a handy, trustworthy ground right there. To run the bypass, connect the wire to ground; to go back to normal behavior, disconnect the wire from ground.

    I need to figure out the clutch pedal problem before winter returns. I just don't want to pull transmissions in the winter.

    Ol'Rattler, if you are reading this, please let me know how you solved your clutch pedal problem. Was it something inside the bell housing or did you just replace the clutch position sensor?
     
  10. Ol'Rattler

    Ol'Rattler Well-Known Member

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    Post 2 tells the tale:

    http://forums.tdiclub.com/showthread.php?t=303285&highlight=height

    In a nutshell, what happened with my new clutch is that the release fingers were to low causing the slave to bottom out while the master still had travel. The cause was an improperly made/machined flywheel.

    More related stuff that's pretty old so may or may not apply:

    http://forums.tdiclub.com/showthread.php?t=141405

    Almost forgot, the clutch position interlock is not a switch, it is a proximity sensor mounted to the side of the M/C. It works similar to a Hall effect sensor and trying to bypass it might damage the ECU since the sensor's output goes directly to the ECU.
     
    Last edited: Aug 25, 2017
  11. csigona

    csigona New Member

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    I just replaced the clutch set and now the clutch pedal descends fully, so I removed the bypass wire I wrote about. I'm happy to report that there was no lasting effect from having shorted the bypass (purple) wire. Neither the ECU nor the sensor were damaged. I appreciate Ol'Rattler's warning, though, about being careful when fiddling with the sensor wires.

    Yes, the clutch pedal sensor is indeed a Hall effect sensor, but it acts like a switch, indeed like two separate switches. I guess that the electronics in the sensor transforms the analog sensor output to on/off voltages just like a switch. One, so to speak, switch notes when the clutch pedal starts moving (so as to disable cruise control); the other notes when the clutch pedal reaches the end of travel (so as to enable the starter solenoid).
     
  12. Ol'Rattler

    Ol'Rattler Well-Known Member

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    Car:
    06 TDI Jetta
    Location:
    Marysvile, WA.
    On modern aircraft we have something called "proximity sensors" on landing gear, entry doors and flight control mechanisms etc. Those usually have 2 states. near or far. My best guess is that the clutch prox sensor on a car is like the aircraft one except it has a Near/far for clutch all the way out and a Near/Far for clutch all the way to the floor. Kinda like 2 sensors in one package.

    Remember the older German cars were if you killed the engine and there was a mechanical part of the ignition switch that blocked the start position until you turned the switch to off and then back on to re-start? That function is now done by software in the ECU. If you kill a modern German car you can turn the switch to start but the logic in the EEC will not send a start command to the starter because the ignition has not been cycled to off and then back on.

    What really bothers me, even with all the bleeding edge digital technology designed into modern cars, is that the only interface available to the driver other than ABS, steering and ESP lights is a single imbecile (idiot) light that only illuminates for emission related DTC's.

    With zero additional hardware, that lame touch screen double DIN Navi they just love to put in cars ($) could have a maintenance menu accessible to the technician and even the driver under specific conditions.

    Aircraft manufacturers have been doing this with the maintenance computer on aircraft for years. In flight only flight required informations and functions are enabled and on the ground the maintenance computer is fully functional for maintenance purposes.

    When the flight crews observes in flight what is called a flight deck effect or a system fault message is displayed, they can press a button and the computer will take a snap shot of pretty much every system on the aircraft for later analysis by maintenance. Yup, and all we get as drivers is single OBD2 imbecile light................
     

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