Touareg 7L 3.0 V6 TDI Brake Assist Workshop

Hi.

I bought myself a new toy, stupidity has triumphed over reason .

"I've already fixed quite a few things, like the intake manifold flaps and the gas struts for the tailgate... and, in addition to other issues, there's the problem mentioned in the title. The previous owner bought it with this issue and just lived with it, so now I'm stuck with it."

The problem occurs when I put the car in reverse and it starts rolling backward, sometimes immediately, sometimes after a few meters. It beeps, and the following error message appears on the display. When I read the ABS control unit, I get the attached error message.

I've already tried using Google, but unfortunately, I haven't found a solution yet. I'm really motivated to figure this out, and it would be great to get some help here!

Thank you.

I would first examine the ESP SG to see if it is possibly damp, rotten, or corroded.

Regards,

For simplicity's sake, I would check the reverse gear switch and its wiring.

I've already replaced the switch, and the wiring seems to be in order as far as I can tell. The reverse lights come on when the car is in reverse.

The error message remains.

I would investigate the troubleshooting process based on how the ESP control unit receives the signal that reverse gear is engaged. I suspect that the reverse gear switch is not directly connected to the ESP, but rather to another control unit, which then communicates with the ESP via the bus (or another wire?). Therefore, first check whether the reverse gear is always recognized by the actual TCU (Transmission Control Unit) in the event of a fault. (Log the channel!) If that bit were to momentarily switch, it could explain your error.

Overall, I suspect the error occurs when the direction of travel detected by the ESP doesn't match the direction indicated by the reverse gear. So far, we've primarily relied on the ESP functioning correctly, but the reverse gear signal seems to be the issue. But is the reverse also possible?

What happens if you drive in Neutral on a hill for a longer distance, either uphill or downhill? Could this provide a clue as to the cause? (That's my speculation.) The ESP might incorrectly detect the driving direction because some other sensor is not functioning properly.

Thanks for the help so far. I'll get around to it once I've registered the car, and I'll let you know or ask further questions then.

I registered it yesterday, but currently, the error message appears as soon as reverse gear is engaged, and the car doesn't move even a millimeter.

What I've also noticed is that when I put the car in reverse, the automatic climate control switches to recirculation mode... Gear out, it switches back.

Hello,

Based on the error symptoms, I suspect that the ESP (Electronic Stability Program) may have been replaced with a version that is not entirely compatible. Or, they built a complete car by combining parts from two defective cars, using a corresponding mix of engine control units.

If the climate control system switches to recirculation mode when reverse gear is engaged, that information should be available on the bus as expected.

Do you have a wiring diagram that shows which control unit processes the reverse gear switch signal and transmits it to the bus?

Best regards, Rainer.

Rüdi wrote:

I registered it yesterday, and currently, the error message appears even when reverse gear is engaged, and the car doesn't move even a millimeter.

Okay, that eliminates all sensors that detect rotation (wheel sensors, speed sensors in the transmission, and similar devices).
In my opinion, this leaves only one possibility: that a discrete signal is not compatible with a bus message. Or, as Rainer wrote, that individual messages do not match the built-in STGs.

Rüdi wrote:

Something else I noticed is that when I put the car in reverse, the automatic climate control switches to recirculation mode...... Gear out, it switches back

Welcome to a modern vehicle .
That's normal for vehicles of that production year and is a characteristic found in at least a significant portion of the VAG group's product range. It's probably designed to prevent exhaust fumes from entering the passenger compartment.
At the same time, the air conditioning system will also be activated (if it had been manually deactivated), and in older vehicles, this will produce the usual "AC start-up noise" during longer reverse maneuvers.

Regards,
Guste.

Thank you for the information; since my cars are almost all over 20 years old, I am not yet familiar with such a "luxury."

I've also consulted "Dr. Google" regarding this problem with the T-Reg, and it seems like this issue is a recurring one, with mentions of it all over the internet, often even in brand new vehicles of this make. Even Volkswagen hasn't been able to fix the problem over the years, so it's definitely not an isolated case.

Hi,

Is the ESP software up to date? You might want to search for the part number on Google and compare the software versions.

Best regards, Rainer.

Do you perhaps have a VW dealer you trust to whom you could show the Touareg? If you're lucky, they might give you further advice on what needs to be checked.

"The car was sold from the farm two weeks ago, 450km away. I fixed the minor electrical issues so that the brake assist and all other safety-related functions work as they should. The Dekra inspector was also satisfied."

While there's still something to be said for the Touareg, even after 10 months of ownership, I don't want to constantly worry about some warning light coming on in the instrument cluster. I'd rather stick with my used cars from the scrapyard.

I'm currently getting my 2003 Passat Variant 2.5 TDI 4-Motion ready for winter use after it had been sitting idle for 1.5 years.

Rüdi wrote:

...I fixed the problem with the small electrical issues, so that the brake assist and everything else that is safety-related functions as it should...

How does that work? Replaced functions with wiring or simulation?

Herbert.

...this vehicle has a brake pressure sensor on the master cylinder... which sometimes displays a reading of 1000 bar even when the brakes are not being applied... Exchanging is good.

SG
Manfred.