Transmission Control Unit (TCU)

Hello,

I recently had my Audi A3 diagnosed because it doesn't start properly when it's been sitting for a while and it's cold outside, and this is what the diagnostic tool showed!
Chassis Type: 8L - Audi A3/S3
Scan: 01, 02, 03, 08, 15, 17, 22, 35, 37, 45, 54, 55, 56

Address 01 -------------------------------------------------------
Controller: 038 906 018 BP
Component: 1.9L R4 EDC G000AG 2110
Coding: 00001
Shop #: WSC 06313
1 Fault Found:
18034 - Powertrain Data Bus: Missing message from Transmission Control Unit (TCU).
P1626 - 35-10 - - - Intermittent
Readiness: Not applicable.

Address 03
-------------------------------------------------------
Controller: 1J0 907 379 H
Component: ABS/EDS 20 IE CAN 0001
Coding: 13304
Shop #: WSC 06435
1 Fault Found:
01315 - Transmission Control Module.
49-00 - No Communications

Address 08 -------------------------------------------------------
Controller: 8L0 820 043 D
Component: A3 KLIMAVOLL
Note: Excessive communication errors.

Skipping Address, 15 Airbags.

Address 17 -------------------------------------------------------
Controller: 8L0 919 880 D
Component: AB-KOMBIINSTR. VDO D08
Coding: 04040
Shop #: WSC 00000
IMMO-IDENTIFICATION NUMBER: AUZ7Z0W0791500
No fault code found.

01315 - Transmission Control Module.
49-00 - No Communications

Address 08 -------------------------------------------------------
Controller: 8L0 820 043 D
Component: A3 KLIMAVOLL
Note: Excessive communication errors.

Skipping Address, 15 Airbags.

Address 17 -------------------------------------------------------
Controller: 8L0 919 880 D
Component: AB-KOMBIINSTR. VDO D08
Coding: 04040
Shop #: WSC 00000
IMMO-IDENTIFICATION NUMBER: AUZ7Z0W0791500
No fault code found.


Now I wanted to ask what that actually means? Does that have anything to do with starting something, or not?


Best regards,
Franz

Hello Franz,
What kind of transmission does your car have?
Manual transmission or automatic?

Best regards,
Rudi

Hello,

My car has a manual transmission, but it's coded as an automatic! That's probably the problem, right?

It was once re-programmed to start more easily! (I completely forgot about that.)

Could it be that my water temperature sensor is broken and displaying a higher temperature than the engine actually has, which then prevents it from preheating? And where can I read this information?

Thank you for the quick response.

Best regards,
Franz

... it's coded for automatic! that's probably the error, right?
Yep! That's why there are error messages.
It was once re-tuned to make it start better! (I had completely forgotten)
While this (often) solves the warm-start problem, it also...
Regarding side effects (e.g., GRA not disengaging with the clutch, ...).
Could it be that my water temperature sensor is broken and displaying a higher temperature than the engine actually has?
Nothing is impossible.
and then not preheated?
That would be the logical consequence.
and where can I read that from??
MWB 007; after a sufficiently long idle time (engine cooled down), all three values should...
move within the same order of magnitude (namely, the order of magnitude of the ambient temperature).

Best regards,
Rudi

Hey, THANKS!!!!

I'll have to try that out tonight!

Sure, no problem!

Best regards, Franzl.

Hi, I just had my car scanned, and it showed me these values at an ambient temperature of 11.5°C!

Fuel Temperature: 31.5 °C
Intake Air Temperature: 26.1 °C
Coolant Temperature: 28.8 °C

What does that mean for me? Are all of these sensors now defective?

I also switched the transmission back to manual mode, and then the error codes disappeared!

Best regards,
Franz

Hello Franz,
If you've already driven the car today, the readings should be accurate.
You could read the data tomorrow morning (before the first start).

Best regards,
Rudi

Hello Rudi,

I read the error codes before starting, as you suggested.

The values were recorded at an ambient temperature of -1.5°C!

Fuel Temperature: 9.3°C
Intake air temperature: 8.2°C
Coolant: 7.2°C. This is the first time it has been preheated!

Could it be that all the sensors are displaying readings that are off by about 10°C?

Best regards,
Franz

Hi Franz,
I'm going to try to take a look at my car tomorrow morning.
How big the differences are.

Best regards,
Rudi

Okay...
Environment: 7°C.
Fuel: 11°C
Intake air temperature: 9°C.
Cooling water: 8°C.

The values are therefore much closer to the ambient temperature than yours are.

I don't believe that all the sensors have the same error. Based on my gut feeling,
I'm leaning more towards the sensor mass (are any additional devices connected?).

Best regards,
Rudi

Hello Rudi,

I had the same thought about the mass. But according to the wiring diagram, the signals supposedly go from the control unit to the respective sensors and then back to the control unit!

Yesterday, I connected a potentiometer in series with the fuel temperature sensor, and then I was able to adjust the displayed temperature!

Question: If a sensor is defective, does the control unit then assume a default value?

"Unfortunately, I need to replace the water temperature sensor; hopefully, that will fix the problem and everything will be okay again."

Maybe she'll think of something else.

Best regards,
Franz

Hi Franz,
Even if the sensors are completely discreetly wired, this refers to...
Signal to the sensor ground, which is also connected to, for example, the mass airflow sensor.

The replacement value for a faulty G62 sensor is approximately the fuel temperature - which would also make sense in this context.
Since the donor isn't that expensive, it's worth a try.
You can also try connecting a potentiometer in series with the G62 and observe the displayed temperature.
If it changes, it's not a fixed value.

Best regards,
Rudi

Hi, I bought the temperature sensor and I'm going to install it now! I'll test it out! Best regards, Franz.

Good morning!

I got the TFW yesterday, but it didn't do anything! Then I connected the mass of all the sensors directly to the chassis mass, but nothing changed! The voltage and ground of the control unit (STG) are the same as the battery. I'm completely lost now and don't know what else could be the problem . Maybe the control unit (STG) is defective?

Best regards,
Franz

Hello Franz,
Have you ever checked it using a potentiometer (like the kind used for temperature sensors)?
Does the value change regardless of the fuel temperature?
If he does that, I would check the value of something before replacing the ECU.
a suitable series or parallel configuration (I have the sensor characteristic curve).
(currently unavailable) and artificially lower the value by approximately 10°C.

Best regards,
Rudi

Okay, I've tested it, and the values are independent! I'm now going to add a potentiometer, probably in the kOhm range. I'm using the values from Autodata, which is a CD from the ARBÖ (a car club, similar to the ADAC).
Das STG wird ja auch ziemlich teuer sein. Or?

Well, thank you very much anyway.

Best regards,
Franz