No more stop/start.

[drivesafe]

About a month ago, I read where by disconnecting a two wire plug on the Negative ( - ) battery terminal clamp, the STOP/START function no longer works.

I disconnected the plug a month ago and the STOP/START function has not worked since.

I wanted to check that this did not cause any error messages to be generated, and to date, nothing out of the ordinary has happened.

I also needed to monitor the operating voltage of the alternator, as I suspected the operation of the alternators voltage levels may be effected by this mod.

I needed to monitor the charge voltage as I occasionally use a second battery and wanted to see if this was going to be effected.

The operating voltage stays at a steady 13.6v to 13.85v at all times in any operating condition.

Again, this has not caused any adverse charging problems and because the voltage does not drop to 13.0v as it normally would, the charging of both batteries is actually improved.

[DV52]

About a month ago, I read where by disconnecting a two wire plug on the Negative ( - ) battery terminal clamp, the STOP/START function no longer works.

I disconnected the plug a month ago and the STOP/START function has not worked since.

I wanted to check that this did not cause any error messages to be generated, and to date, nothing out of the ordinary has happened.

I also needed to monitor the operating voltage of the alternator, as I suspected the operation of the alternators voltage levels may be effected by this mod.

I needed to monitor the charge voltage as I occasionally use a second battery and wanted to see if this was going to be effected.

The operating voltage stays at a steady 13.6v to 13.85v at all times in any operating condition.

Again, this has not caused any adverse charging problems and because the voltage does not drop to 13.0v as it normally would, the charging of both batteries is actually improved.

@drivesafe: Hi. I'm delighted to read of your firm conviction that removing the connector on the Battery Monitor Control Module (it's called "J367" on the wiring diagram) has no adverse ramifications.

As I read your analysis, at the heart of your conviction is the notion that pulling the J367 connector has no impact (other than disabling Start Stop (SS)) because monitoring Start Stop is it's ONLY function

Without intending any offense, alas I don't share your belief - for the following reasons:

Here's a diagram showing how J367 is connected:



As you can see, J367 is a LIN slave to the "Data bus diagnostic Interface" module (this is called "J533") and it happens to share this communications wire with the same wire that the alternator uses to talk to J533.

So, the fact is that J367 does indeed have multiple roles on MQB platform vehicles (like your gen2 Tiggy); it's primary function is to provide a constant stream of real time data about the battery (via the LIN comms line shown above) to the car's Energy Management System (EMS). This data includes (but is not limited to) Battery voltage, Battery temperature (the EMS uses an algorithm for this) and a complete history of electrical current drawn from the battery and injected into the battery over its life cycle. This data stream is used by the EMS to make decisions like:

• If there is sufficient battery capacity to re-start the car if SS switches off the engine
• How much "headroom" there is on the battery for the injection of additional amps from the energy recouperation facility
• how to modulate the alternator charging current over time so as to optimize the longevity of the battery based on the settings that are recorded in J533 about the battery (like manufacture type, rated battery capacity and date of battery installation)

The reason why pulling the connector from J367 is the (supposed) fix for SS is that the EMS has no information about this part of its decision making role, so it thinks the there is insufficient battery capacity to re-start the engine.

And, the reason why it's vitally important NOT to connect the negative battery cable from a jump-start battery, or battery charger directly to the negative battery terminal of the car battery is because it by-passes J367. If J367 is by-passed, it means that the EMS does not measure the amperes being injected into the car battery by the external device - which in turn means that the true history of the battery is lost - which means that the EMS cannot correctly modulate alternator charging current over time to optimize battery longevity.

So, as I have suggested, J367 is part of the car's wider energy management function and removing the data stream is NOT a trivial matter, or a matter that affects just SS.

My suggestion is to replace the connector immediately so that the battery history file on the EMS is not further corrupted. If you want SS disabled, do it properly via a tweak from a diagnostic device, or install/make an auto SS kill switch (I've designed a few which you can find on the Golf mk7 forum)

Don
PS: I also have disabled SS on all my cars - but I would never do this by disconnecting J367. And, disconnecting the cable to J367 does indeed result in an error which is shown on a diagnostic report from VCDS, OBDeleven, VCP, ODIS etc.

[drivesafe]

Hi DV52 and thanks for the info, that was an excellent read.

At this stage, as there are no problems being caused by unplugging that lead, I am very happy to leave it that way, to keep the STOP/START function permanently deactivated.

One observation is that over the last couple of days, the temperature up here has dropped and I am logging a slightly higher constant operating voltage.

It now runs as high as 14.05v, so the vehicle does seam to be setting the voltage based on temperature.

As the higher operating voltage means higher charging current, this is an even better result.

But this all needs to be studied for a much longer time, before any real conclusions are arrived at.

Again, thank for the info.

[Hillbilly]

Hi DV52 and thanks for the info, that was an excellent read.

At this stage, as there are no problems being caused by unplugging that lead, I am very happy to leave it that way, to keep the STOP/START function permanently deactivated.

One observation is that over the last couple of days, the temperature up here has dropped and I am logging a slightly higher constant operating voltage.

It now runs as high as 14.05v, so the vehicle does seam to be setting the voltage based on temperature.

As the higher operating voltage means higher charging current, this is an even better result.

But this all needs to be studied for a much longer time, before any real conclusions are arrived at.

Again, thank for the info.

I would take DV52's advice against what you "think" is not causing a problem.. Because if you keep on doing it when you find out whats gone wrong it might be too late.

There have been several threads in other Forums who back up his explanation so i would be taking it in the spirit it is offered.


These are not your 20yr old 4x4 which you could run with stuff altered or disconnected and it still ran.

The electrical systems in VW's are complicated and are run by the BCM and should things not be running according to its program nasty things can happen.

So best to leave alone what you arent sure about or try a method that has proved to work without upsetting things.

If you have a 3 year old Tiguan its dead easy to turn off S/S if its a new one VW have deliberately stopped you from turning it off.

Apparently the switch which can be inserted in the wiring loom works and doesnt interfere with BCM

[DV52]

Hi DV52 and thanks for the info, that was an excellent read.

At this stage, as there are no problems being caused by unplugging that lead, I am very happy to leave it that way, to keep the STOP/START function permanently deactivated.

One observation is that over the last couple of days, the temperature up here has dropped and I am logging a slightly higher constant operating voltage.

It now runs as high as 14.05v, so the vehicle does seam to be setting the voltage based on temperature.

As the higher operating voltage means higher charging current, this is an even better result.

But this all needs to be studied for a much longer time, before any real conclusions are arrived at.

Again, thank for the info.

Drivesafe: I think that I might owe you an apology - when I replied to your post, it most definitely wasn't with the intention of trying to disabuse you of your beliefs about the J367 plug! You are (and you should always remain) free to hold whatever views you want regarding this matter.

My response was simply intended as a suggestion (advice, really) based on my research of the topic.

IMHO, there is no greater fool on this fragile blue planet than someone who believes that truth has only one face !! So indeed, it's entirely possible that my understanding of the Energy Management System on MQB platform vehicles is wrong and that your views are correct. If so, then respect!!

Don

PS: on the slim possibility that my understanding is correct- a factor to consider is how corrupted the data history file is on your car because it hasn't been able to record battery charge-in/out. As you have only had the plug disconnected for a month, it's perhaps not a big issue at this point in time. But as time increases with the plug disconnected, the lost data becomes increasingly more important. Again, this is not a problem if your views are correct.

PPS: on the matter of your battery voltage measurements - the EMS system on MQB platform vehicles that have J367 installed won't allow the alternator to fully charge the battery. This is because a battery capacity "headroom" is needed to accept additional amps from the car's recouperation facility. This requirement is a fundamental law of physics and I would be very surprised if VW contemplated the automatic removal of the battery headroom in instances where the J367 plug was disconnected (and recouperation was disabled)

With early MQB cars, VW allowed drivers to view the battery State-of-charge (SOC) measurement which invariably showed 80% . This facility was withdrawn in later models because (I suspect) drivers kept complaining to VW

[drivesafe]

Drivesafe: I think that I might owe you an apology

Hi again DV52 and I did do take your post as anything but informative, so you have nothing to apologies for.


Hi Hillbilly and I have been working with SMART alternators since they first became commonplace back around 2004.

I have worked on and had feedback from others who have worked on many different makes and to date, I have not come across a single issue caused by disconnecting communication wiring on a number of makes of vehicles, but as stated, I have only been testing the Tiguans operation for a little over a month now, so still early days yet.

As to the modification to the STOP/START Activation/Deactivation switch. Shortly after I bought me Tiguan 4.5 years ago, I programmed a small micro to use as an automatic deactivation device, but I just did not want to pull the centre console apart ( and did not know how to ) so it was never installed.

The disconnection of the plug is far simpler and is proving to have other advantages.

[Hillbilly]

Hi again DV52 and I did do take your post as anything but informative, so you have nothing to apologies for.


Hi Hillbilly and I have been working with SMART alternators since they first became commonplace back around 2004.

I have worked on and had feedback from others who have worked on many different makes and to date, I have not come across a single issue caused by disconnecting communication wiring on a number of makes of vehicles, but as stated, I have only been testing the Tiguans operation for a little over a month now, so still early days yet.

As to the modification to the STOP/START Activation/Deactivation switch. Shortly after I bought me Tiguan 4.5 years ago, I programmed a small micro to use as an automatic deactivation device, but I just did not want to pull the centre console apart ( and did not know how to ) so it was never installed.

The disconnection of the plug is far simpler and is proving to have other advantages.

If your Tiguan is a MKII you could have turned the S/S off in 30 secs using the voltage method and not had to make or pull anything apart.

I and others would doubt your last sentence especially after reading DV52's very descriptive posts

[drivesafe]

Hi again Hillbilly, I'll find out in due course, if there is a problem, but as stated above, as I have now gained other advantages, such as the constant higher operating voltage, I like what is now happening and will keep this as is.

Furthermore, the fact that both the STOP/START function no longer works, which means the cranking battery is going to have an easier time, plus again, the fact the operating voltage is higher and more constant. These two factors, combined with VW using STOP/START type cranking batteries, should guarantee a much longer cranking battery lifespan.

Only time will tell, and as highly unlikely as it seems, but if I do have any problems, I will post them up here quick smart.

[drivesafe]

Hi folks and just an Update.

It’s been nearly 12 months since I first disconnected the Battery Monitor from the negative ( - ) terminal on the cranking battery.and so far not a single issue with the Tiguan.

But I have had some interesting effects on the dual battery system’s auxiliary battery.

I initially had an AGM auxiliary battery but decided to test a lithium auxiliary battery.

With the Battery Monitor disconnected, and a reprogrammed isolator fitted, the lithium battery not only charged well but it also helped maintain the Tiguan’s cranking battery at a higher settled voltage.

For a short time, I experimented with the lithium battery fitted and the Battery Monitor reconnected.

This DID NOT work, because a lithium battery always sits at 13.3v, until it is near fully discharged, so the Tiguan’s BMS would see what it considered to be a fully charged cranking battery and would lower the alternator voltage.

This meant that the Tiguan’s own power requirements were being supplied only from the lithium battery.

I did not discover this until I went on a long drive and noticed the voltage had dropped from 13.3v down to 13.13v, meaning the lithium was down below 20% capacity.

I immediately disconnected the Battery Monitor and the Lithium battery was near fully recharged on the return 1 hour+ drive home.


Anyway, disconnecting the Battery Monitor has had zero effect on the operation of the Tiguan, other than deactivating the STOP/START function.

[masster]

This topic made me register for this forum.
Here is my opinion. Although in theory, BCM should do a great job, in reality, it doesn't allow the battery to charge more than 50%. Most of the time the battery has 12.2 V in the morning. I tested if there is a parasitic draw and the car sleeps rather quickly to about 5mA consumption overnight.
I own a Tiguan Mk1, 2015, 1.4 TSI 122hp R-Line, with a Start/Stop function and a button on the centre console to disable it. Most of the time I disable that stupid feature. Several times I had the unpleasant surprise of not being able to start the engine.
Of course, we don't have the luxury of having clearly displayed on our dashboard the State of Charge (SOC) of the battery, which should be mandatory. Why isn't BCM doing that beats me. It would be more useful than a simple battery red alert indicator.
Nevertheless, I will disconnect J367 too because I can't risk myself to get stuck in traffic or at home just because the BCM does a poor job. By the way, my Varta 65 Ah battery is special for the start/stop feature and I coded it correctly using VCDS.