Weird issue with Gear Indicator and Cruise Control

[dantwah]

I've identified something new with it; related to not recognizing the 5th/6th gear properly. Which is the following:

 

-> When the car recognizes gear, and I release the throttle (gas pedal), the car smoothly reduces speed/gas

-> When the car doesnt recognize the gear, it bonks /shakes a bit when I release the throttle. 

 

This happens simultaniously when the car doesn't recognize the gear; for example, in 6th, same speed; and I release throttle while the car recognizes the gear, it goes smooth. When it doesn't, it bonks/jerks a bit when I release the gas. 

 

This makes me think it might be something in the gearbox; like the synchronizers or linkage. What do you guys think? Any idea on what that can be? Or is it just the computer responding 'weird' as it doesn't know which gear it is in. 

 

Thanks,

[J.R.]

It will not be anything mechanical in the gearbox like synchromesh cones or the linkage causing your problem so forget that.

 

There are no electrical sensors either, the ECU decides which gear the vehicle is in by comparing the engine revs with the speed sensor which I suppose is a transmission sensor.

 

Your problem is most likely to be the clutch position sensor on the master cylinder.

[dantwah]

Hmm got master cylinder & clutch sensors replaced. It also only occurs in 5th and 6th gear. Is there a sensor only for 5th and 6th gear? 

[Breezy_Pete]

Vehicle speed sensing will be done by the ABS module and wheel speed sensors. 

[dantwah]

Hmm but with vehicle speed sensor it doesnt make sense its only 5th and 6th gear. In 4th and lower it all recognizes it correct.

[J.R.]

Do a forum search, via Google is the best, another contributor had exactly the same problem spending a lot of time to finally resolve it, from memory even a replacement master cylinder was faulty. I think his main problem was the cruise control not working but the secondary oddity of the gear display was the key factor in suspecting and identifying the clutch pedal sensor

 

Same 5th and 6th gear issue, I cannot explain why it would only affect those indicated gears but a problem with the clutch pedal sensor will prevent the display from functioning correctly.

[dantwah]

3 hours ago, J.R. said:

Do a forum search, via Google is the best, another contributor had exactly the same problem spending a lot of time to finally resolve it, from memory even a replacement master cylinder was faulty. I think his main problem was the cruise control not working but the secondary oddity of the gear display was the key factor in suspecting and identifying the clutch pedal sensor

 

Same 5th and 6th gear issue, I cannot explain why it would only affect those indicated gears but a problem with the clutch pedal sensor will prevent the display from functioning correctly.

 

I think that was still me haha :), just didn't get it resolved yet sadly. 

 

I think as well that the cruise control is just a 'symptom' of a different system not working / communicating correctly. What is even more weird is that that its mainly in 5th and 6th gear only. If it's somewhere with pedals, I would assume it happens with all gears. A transmission speed or vehicle speed -maybe. But I've tried to put the car on the same speed in 4th gear (instead of 5th), and all works fine. So I'm guessing wheel sensors are fine then. 

 

I've had it checked by Skoda, independent shops, but none really could figure it out (and gave up pretty quick as well). No error codes or none. A sensor or loose wire still makes sense, if it's related to 5th / 6th gear. Or a loose'ish bracket or something that makes it thinks it goes into the neutral sensor? Diagnosing hasn't given any other solutions. 

 

Is there a way to approach it to find the solution? Do like a full electrical test or whatever? 

[Urrell]

2 hours ago, dantwah said:

A sensor or loose wire still makes sense, if it's related to 5th / 6th gear

That would make no difference, no sensor in gearbox relating to any gears.
My Fabia lost cruise control due to a crack in the plastic vacuum pipe to servo, took ages to find that.

[Breezy_Pete]

I think it must be getting bad data from one of the wheel speed sensors.

 

I can't see it being the input for rpm from the crank angle sensor (that would manifest itself in any gear), and as JR has said, the calculation of gear display will be from that and vehicle speed, which I believe is calculated by averaging between some or all of the wheel speed  sensors. The error may get bigger with wheel speed, until it reaches a point where the calculation result doesn't make sense to the programming, and it starts displaying wrong info or no info on screen, and cruise is disabled.

 

Try to get someone with VCDS to come for a ride with you and watch/log the outputs of the four wheel speed sensors simultaneously and then see if there is one sensor that starts to show data that diverges from what the others are saying at higher road speeds.

[J.R.]

Well thought through Pete and a very plausible proposition 👍

 

5th and 6th gears are very close and are the only ones used in the upper speed ranges.

[J.R.]

1 hour ago, Breezy_Pete said:

Try to get someone with VCDS to come for a ride with you and watch/log the outputs of the four wheel speed sensors simultaneously and then see if there is one sensor that starts to show data that diverges from what the others are saying at higher road speeds.

 

I'm sure the OP and most readers would realise but I would add the caveat "driving in a straight line"

[MCAMRA]

If it is a wheel speed sensor or somthing related…????……which sounds likely…..
 

Could you just not clean with a karcher (gently) the wheel assembly under the car and see what happens.

 

It might simply be a bit or dirt, mud, gravel that has got stuck in the wrong place giving the sensor/electrics a headache.

 

Disclaimer….I am not a mechanic. But that is what I would do.

 

 

[Urrell]

7 hours ago, Breezy_Pete said:

Try to get someone with VCDS to come for a ride with you and watch/log the outputs of the four wheel speed sensors simultaneously and then see if there is one sensor that starts to show data that diverges from what the others are saying at higher road speeds.

Would that not set off the tyre pressure monitoring alarm?

[Breezy_Pete]

I think this car may predate such a system? @dantwah does the car have tyre pressure monitoring?

It ought to set some sort of fault in the ABS module if the error is big enough and happens often enough, but maybe it doesn't meet those criteria.

 

[J.R.]

5 hours ago, MCAMRA said:

Could you just not clean with a karcher (gently) the wheel assembly under the car and see what happens.

 

It might simply be a bit or dirt, mud, gravel that has got stuck in the wrong place giving the sensor/electrics a headache.

Indeed you could and what you will see happens is precisely nothing, its a hall sensor with built in magnet triggered by a reluctor ring if thats the right word, the segments diminish the magnetic field being seen by the hall sensor creating a pulsed waveform, it is designed to operate in the hashest environment, it will have experienced the equivalent of a Karcher each time you drive through standing water.

 

They are very well sealed if the connector was pushed home correctly and is undamaged, nonetheless I would never dreal of pressure washing one any more than I would think of pressure washing the main ECU.

 

There is also the danger of water ingress to the CV joint and wheel bearing.

Edited 15 August, 2023 by J.R.

[muddyjim]

On 14/08/2023 at 18:49, dantwah said:

 

 

-> When the car recognizes gear, and I release the throttle (gas pedal), the car smoothly reduces speed/gas

-> When the car doesnt recognize the gear, it bonks /shakes a bit when I release the throttle. 

 

 

I think that points to a clutch switch/sensor problem;

 

I used to have a diesel x-type jaguar. Someone on an x-type forum was having trouble making smooth gear changes. It was discovered that a switch on the clutch pedal should slow the engine down when the clutch pedal was pressed down.  

 

I tested this on my x-type. If I drove along at say 30mph and slipped the car into neutral (without touching the clutch) and then immediately released the throttle, the engine would carry on revving for some time, however if I dabbed the clutch pedal, the revs would immediately drop.

 

 

Edited 15 August, 2023 by muddyjim

[dantwah]

3 hours ago, Breezy_Pete said:

I think this car may predate such a system? @dantwah does the car have tyre pressure monitoring?

It ought to set some sort of fault in the ABS module if the error is big enough and happens often enough, but maybe it doesn't meet those criteria.

 

oh its a modern one with TPS! Found out the hard way not so long ago :), great usefull system, that u dont know you need until u need it 😂. So yes, it has the tire pressure monitoring.

 

I went to drive with OBD11 plugged in, live data on the weel sensors (in straight line, safe etc etc). They all give the same speed reading, no irregularities there. Definitely was a good idea tho - as it somewhat makes sense. Especially with 5ath and 6th gear not being so super different (I almost dont get that there is a 5th). 
in the 5th it sometimes flickers between thinking its in 5th or 6th untill it goes doesnt show any. Maybe it might be with engine speed sensor, similar idea that higher speed, the margins are smaller?

[Breezy_Pete]

Fair enough. I wonder if @muddyjim may be right then. Can you (with an assistant) monitor the status of the clutch pedal switch while driving, looking for data/status errors there?

[dantwah]

12 minutes ago, Breezy_Pete said:

Fair enough. I wonder if @muddyjim may be right then. Can you (with an assistant) monitor the status of the clutch pedal switch while driving, looking for data/status errors there?

 
Can try to do that this. Ive already got the sensor changed recently (and master & slave cylinder), but will do the test tomorrow! Any other sensors to monitor that we can think of?

[MCAMRA]

11 hours ago, J.R. said:

Indeed you could and what you will see happens is precisely nothing, its a hall sensor with built in magnet triggered by a reluctor ring if thats the right word, the segments diminish the magnetic field being seen by the hall sensor creating a pulsed waveform, it is designed to operate in the hashest environment, it will have experienced the equivalent of a Karcher each time you drive through standing water.

 

They are very well sealed if the connector was pushed home correctly and is undamaged, nonetheless I would never dreal of pressure washing one any more than I would think of pressure washing the main ECU.

 

There is also the danger of water ingress to the CV joint and wheel bearing.

The tyre pressure warning light on my transporter van kept coming on during long journeys. I would stop, check the pressures and they would be fine. Press reset. Get to my destination and check again. And they would be fine. This happened a good five times in a row.
 

One day I cleaned the van (because it was dirty…not because of the warning light problem) and the wheels with a karcher. Since then, the tyre warning light has not come on. Coincidence ? I have no idea. But it is back to normal.

 

A better one.

 

Last spring the emissions warning light came on the Yeti. The manual said go straight to a Skoda garage and pay money. So we did. They tested the car and it was fine. In fact the light went out. But recommended paying a lot of money to clean something. Which we declined.

 

Coincidentally, whilst waiting for the car, another person came into the garage saying that their emissions light was on. I think it was a tiguan. I suspect a lot of people came in that day with the same problem.

 

I realised that we were on red alert that day for pollution and that must be interfering with the sensor. Reading the atmosphere rather than the car ?
 

Not sure VAG would agree.

 

A couple of days later, the emissions warning light came back on again. It went off when the pollution passed.

 

External factors can influence sensors.

 

Anyway, I hope the op sorts out his problem. It is the type of thing that would drive me mad.

 

 

[dantwah]

Okey, I have maybe been able to get to actually a thing that could make sense; where the error might point to. 

 

I got this on channel 13 (and some others, for rear right, front left, front right). 

 

If I google for 65535 error, I come to things like this: http://wiki.ross-tech.com/wiki/index.php/65535. 

 

Now, i'm not sure if that actually is correct or that it says something completely different. Would this make any sense, and if so, how to resolve it?