Retrofitting a 1.6 TDI DSG engine to a 1.2 TDI manual Polo 6R



Verified VCDS User
Aug 10, 2016
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Eindhoven, NB, NL
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Hello guys, I need some advice.

The big question is, what ECU to take.

The donor car:
Polo 6R 1.6 TDI 2011
- Engine CAYB
- Gearbox DSG7 DQ200 MPT
- No start/stop system

The recipient:
- Polo 6R 1.2 TDI 2011
- Engine CFWA
- Gearbox Manual 5, MQ200 MZN
- Start/stop system

No I'm looking to get an appropriate ECU.
What the ECU needs to have:
- CAYB engie
- DSG software

Now the thing I'm not sure about is the start/stop system. Ideally I'd like to retain the start/stop system since the car is wired to have it.
The starter relays are wired to work this way and there is a difference in, i.e., the operation of the radiator fan and the alternator.

So now there are two options:
- Re-wire the car to make it work without start/stop system and use the donor cars ECU
- Find the appropriate ECU for start/stop, CAY* engine and DSG7
There are ECUs from i.e. the Golf 6 platform that do support CAY, DSG7 and start/stop (PR 7L6).
This way I maintain my emissions class, start/stop system, regenerative braking etc etc.

The question is however, will it work with the car. Will a PQ35 engine control unit run in a PQ25 car.
Oh the hardware side, a CAYB engine in a Golf is exactly the same as a CAYB engine in a Polo.
Down to the wiring, it's identical.

I asked around and some people say 'yes, sure, no problem'. Other say it might not work due to software issues.
Will it talk to the ABS properly (Bosch ESP9.0i instead of MK60EC1)?
This is right now my only concern.
The ETKA search didn't really work either since even within the PQ25 platform, there are different ECU's (Polo, Fabia, Ibiza, Rapid, etc) for a CAYB engine.

There are many modules in my car that are from the PQ35 platform and they all work just fine. It's just this one thing I'm a bit cautious about...

Thanks for your advice.
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Ross-Tech Employee
Ross-Tech Employee
Jan 29, 2014
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16.4905° S, 151.7375° W

Silly question, but I will ask anyways .. :) - Have you considered swapping over all the powertrain components? ECM, TCM and ABS? (and others as needed)

I ask this because I have been kicking around the idea of buying a crashed/rolled Audi RS3 and a flooded A3... I would be swapping over everything on that build because I would want to match the controllers so that there would be no conflicts or other issues.. since they are 'known' to work together.

I would imagine the 'unknown' element of what software is compatible or what is not and what can be changed and what can not would be changed could be a real headache.

Personally, I would rather take the 'donor' parts swap job than the 'unknown' job above... and then add the Start/Stop.

This maybe it is the path of least resistance and it is not necessarily re-inventing the wheel...maybe ???

Just my thoughts,

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