CODES U0456 and P18B0

Hello,

The code P18B0 is due to an issue with the PDK (dual clutch transmission) control module.
Typically, the issue points to a faulty module.

The U0456 refers to fault within the air conditioner control module. Most of the time this does not affect functionality.

What type of issues are you experiencing?

The weak battery should be due to these codes. It could just be old or have bad cell(s).
Have you done a load test on it?

https://www.2carpros.com/articles/car-battery-load-test

I have attached the diagnostics for the P18B0 below.
Please let me know if you have any questions.
Thank you.

I am buying it from an auction tomorrow, with 86,000 hard to believe it already has transmission issues but possible. PDKs u it is electrical so that i can believe. I have not driven it but i take gambles as such. Will let you know what happens. Thanks for your help.

Those PDKs typically have software issues rather than all out bad transmission.

Yes, i read that too, first thing am going to do is check the software on it.

That is surely a good plan. Let me know how it goes.

Where is the PDKs control unit by the way?

That control unit is located under the dash on the driver side. I have attached diagrams below.

Drove it home, nothing funny I am seeing with the transmissions. I think they drove it when it was really cold yesterday, that's why they arbitrated it. These PDKs and SMg transmissions drive poorly when cold, once warm all good. Drove it home. There was also an announcement for differential since they didn't know why there is a noise, which is in the video. Battery was dead i had to jump it and delete all codes first. But as far as the noise, while driving if your foot is on the gas no problem, once you lift off the gas pedal you hear this light grind as if the rotor is rubbing against something. Not sure if you can hear it. I let off and pressed gas more than once to let you hear the difference.

Is the noise coming from directly under the car, from the transmission tunnel?
You might want to inspect the fluid condition. Also it could be gears rubbing due to not enough fluid.

I looked under the rear and rear end is dry no leaks at all but saw some grease on driver side and found the rear axle has spit a lot of its grease from the inner boot all over. Can an axle with little grease cause such grinding noise?

If you have metal to metal contact it will make a grinding noise. Typically, the noise will worsen overtime due to having excessive friction and heat.
It could also have metal shavings due to this friction.

I am guessing i have to put all four wheels off found in order to put it in gear and watch where the noise is coming from. I wish there was a way to have one rear wheel turn to see where it's coming from.

Due to this all-wheel drive, I have dealt with a similar procedure with Audi's as you will have to lift the car in order to hear certain noises. It is easier and safer if you have a lift. Can be tricky with jack stands.

I have a lift. Will all wheel's spin when in drive?

Yes, it will spin. This will likely throw a code. But you can just clear it, if it does.