Disable Stop/start - VCDS tweak

[logger]

In reply to my previous. Collected new Touareg. It has the Acc/Start Auth. Control module. Car has 25km on clock. Module is accessible and was readily able to deselect byte1 bit 5 and disable the Start/Stop function. So will get out of your hair & scoot off back to the 'Reg forum now. Will be interesting to see if the module remains accessible.

[mythik]

In reply to my previous. Collected new Touareg. It has the Acc/Start Auth. Control module. Car has 25km on clock. Module is accessible and was readily able to deselect byte1 bit 5 and disable the Start/Stop function. So will get out of your hair & scoot off back to the 'Reg forum now. Will be interesting to see if the module remains accessible.

Made in Jan '15 Touareg here. Just delivered! Tried a few of the weird and wonderful ways to get rid of the dreaded start/stop nemesis. Not having any success! Any tips??

[DV52]

I'm hoping that there are some forum colleagues out there with an understanding of basic electronics and knowledge of Start Stop (S/S) technology that can help.

As most folk will be aware, there's at least two ways (maybe three) of disabling S/S by fiddling with the car's adaptation channel settings. However, not everyone has access to a VCDS cable. So I was thinking - is there a way of achieving this tweak for those that don't have a cable?

As a factory option, the driver is able to disengage "bluemotion" by pressing the S/S disable button that is located on the centre console. The problem is of-course that the car doesn't remember the centre console switch setting when the ignition is turned-off, so the S/S disable button must be re-activated every time the car is started. This disadvantage notwithstanding, a quick look at the Wiring Diagram (WD) for this part of the car's electrical circuit shows (perhaps "suggests" is a better word) that the S/S disable button is a simple single-throw-single-pole switch.

I've posted a copy of the WD below to illustrate the simplicity of the factory fitted S/S kill circuit. Apart from the LED and the ballast resistor that is connected to PIN #7 which is energised via the BCM when the S/S switch is activated, the actual mechanism for shutting-down S/S appears to be a switch that connects PIN #60 on the BCM to ground (via PIN #4 on the S/S button). Note: the other LED and its current limiting resistor which is connected to PIN #2 on the S/S button is for console panel lighting (terminal 58d) Question 1 - Am I missing anything else?

So, if my analysis is correct, then another way of disabling S/S should be to install a device across the S/S button on the centre console so that it automatically shorts-out PIN #4 to ground whenever the ignition is switched-on. An easy way of doing this (I think) is the simple 555 circuit that is also shown in the picture below. The fix (if it works) only has 6 components and I've arranged the configuration of the 555 circuit so that there is approx 5 sec time delay (after terminal 15 power is energised) before the relay is energised. My thinking is that this delay may be prudent to allow the car's other electronic circuits to stabilise before the S/S kill signal is sent to the BCM. Question 2 - Am I missing anything else?

Comments and views gratefully accepted
Cheers
Don

[AJW]

I'm a Electronics Tech waiting for my GTIPP - should have it in Oct.
This looks like something I might have a go at.
Can't see why it wouldn't work, no difference between you shorting the switch with your finger and a relay doing the same thing.
The only thing I'm not sure about is how "bouncy" the 12V is when you turn the car's ignition on and when you start the car.
This might cause it to trigger again.
Do you know if there's a switched 12V line near the Start/stop switch?

I'd probably try building it with a SMD 555 to keep it as small as possible to hide in the centre console.
If you want to turn on the start/stop you'd just press the button again.

[Lucas_R]

Do you know if there's a switched 12V line near the Start/stop switch?

The cigarette lighter is not far away in the centre console for a switched 12v source.

[AJW]

The cigarette lighter is not far away in the centre console for a switched 12v source.

Yes I thought that might be the case.

Depending on how fussy the control electronics is connected to the switch you could probably use a Solid State relay.
That way there's less things to go wrong.

[DV52]

I'm a Electronics Tech waiting for my GTIPP - should have it in Oct.
This looks like something I might have a go at.
Can't see why it wouldn't work, no difference between you shorting the switch with your finger and a relay doing the same thing.
The only thing I'm not sure about is how "bouncy" the 12V is when you turn the car's ignition on and when you start the car.
This might cause it to trigger again.
Do you know if there's a switched 12V line near the Start/stop switch?

I'd probably try building it with a SMD 555 to keep it as small as possible to hide in the centre console.
If you want to turn on the start/stop you'd just press the button again.

AJW: Hi and thanks for the response

Good point about the switch bounce issue. I'm not sure how problematic this will be but you might consider installing an electrolytic capacitor physically placed near the 555 supply pins and a free-wheeling diode across the supply rail (again near the 555) to handle negative spikes. I also like your suggestion of using a solid state relay, but I suspect that all that is required is a simple transistor switch (something like a BC547). I'm not sure what circuitry is inside PIN #60 of the BCM, but I assume that it's some sort of open collector arrangement.

I've shown an alternative output circuit in the picture below. I've nominally chosen the resistor for the base of the BC547 to be 22k, but you might need to experiment with this value. The output voltage (at PIN #3) of the 555 timer is about 2Volts lower than the supply rail. So assuming a nominal 14 volt supply, the voltage across the base resistor for the BC547 should be about (14-2-0.6) = 11.4 Volts. If a 22k resistor is used, this means that the base current will be a about 0.5 mA. Assuming a nominal transistor gain (hfe) of typically 90, this should allow 45mA of collector current to flow - should be more than ample as the S/S kill signal. Not sure if a pull-up resistor will also be required, but I'd try without one to start.

SMD is a good idea, but I'm not sure if this is entirely needed as the non-smd device shouldn't be that big.

Also, not sure about your comment "If you want to turn on the start/stop you'd just press the button again". Once the circuit is in place and the 555 timer has latched, PIN #4 of the S/S button will be shorted to ground. As the S/S button on the centre console is effectively in parallel with the output relay/transistor, pressing the button won't remove the short to ground (I think). I may have misunderstood your comment - sorry if I have

Cheers
Don

[AJW]

AJW: Hi and thanks for the response

Also, not sure about your comment "If you want to turn on the start/stop you'd just press the button again". Once the circuit is in place and the 555 timer has latched, PIN #4 of the S/S button will be shorted to ground. As the S/S button on the centre console is effectively in parallel with the output relay/transistor, pressing the button won't remove the short to ground (I think). I may have misunderstood your comment - sorry if I have

Hello Don

It's a bit hard because I don't have a car to test but I'm guessing the the Start/Stop switch is momentary not latching.
As the system seems to reset the function when you turn the car off it must be momentary - I'm guessing all the centre console switches are.
So I was thinking of doing a "power-on reset" pulse that latches a relay for say 1/2 sec across the switch every time you power the car on.
Really the same way as pushing the switch every time you get in the car.
That way if you decide to use the Start/Stop you can just press the switch again.
I'm also assuming that as soon as you open the car and get in (even with a Keyless entry car) that the switch is "active" and can be turned off before you start the engine?

The only issue with power-on rest circuits using capacitors for the timing is if you power in on/off/on quickly the timing will be different.
It's probably an edge case in a car, but I've had a quick look and found a few circuits using 555's that will do consistent timing no matter how long they are on.
I've also seen a few dedicated Reset IC's around that might be better to use, might have a look.

Be interested if you can check how the switch is working and if it's active as soon as you open the car.

[DV52]

Hello Don

It's a bit hard because I don't have a car to test but I'm guessing the the Start/Stop switch is momentary not latching.
As the system seems to reset the function when you turn the car off it must be momentary - I'm guessing all the centre console switches are.
So I was thinking of doing a "power-on reset" pulse that latches a relay for say 1/2 sec across the switch every time you power the car on.
Really the same way as pushing the switch every time you get in the car.
That way if you decide to use the Start/Stop you can just press the switch again.
I'm also assuming that as soon as you open the car and get in (even with a Keyless entry car) that the switch is "active" and can be turned off before you start the engine?

The only issue with power-on rest circuits using capacitors for the timing is if you power in on/off/on quickly the timing will be different.
It's probably an edge case in a car, but I've had a quick look and found a few circuits using 555's that will do consistent timing no matter how long they are on.
I've also seen a few dedicated Reset IC's around that might be better to use, might have a look.

Be interested if you can check how the switch is working and if it's active as soon as you open the car.

AJW: OK, now I understand what you said-again my apology for the confusion.

I had omitted to emphasise in my first post that one of my objectives was to keep the component count low. In my suggested circuit, the output of the timer goes high after about 5 seconds -thereby energising the output relay/transistor (which stays energised). The process of shorting PIN #60 on the BCM has the effect of producing a negative edge after the 5 second interval (as I said, I assume that there is some type of open collector circuit in the BCM). It's the negative edge that appears to energise the S/S kill signal

Whilst my circuit keeps PIN #4 shorted, manually holding down the S/S button doesn't appear to do anything - so I don't think that it's a problem. But if you want to add a one shot pulse circuit to the output of my suggestion, then it will be a more sophisticated solution (but the component count increases - ok if you use SMD, I guess).

Cheers
Don

PS: if you do want to add the one pulse circuit, consider using a 556.

[fantomasz]

Anyone can explain how voltage method works? What this voltage limit do? It is safe to do it?