Auxiliary Coolant Pump Fail?

[PSUS4]

Hey guys, sadly I sold my A6 today. The new owners made it six miles when the car overheated. I went to their house to scan the code and found code P1B1C00. After a little research I’m thinking this is a fault with the aux water pump given I’ve replaced the mechanical one and the t stat less than 15k miles ago. I want to be a good seller and replace it for these people. Is this the right diagnosis or am I just throwing parts at it?

Thanks for any help.


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[VinnysS4]

Did you verify the overheating issue? Or did the car throw the coolant light and they assumed it was overheating?! The code is common for 2 things: 1(there is a TSB on this code) defective thermostat. I know it's newer, but very possible it failed. The TSB also says the diagnostic software could be incorrectly displaying the code. And 2: the sensor in the expansion tank can give weird codes like this

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[PSUS4]

Did you verify the overheating issue? Or did the car throw the coolant light and they assumed it was overheating?! The code is common for 2 things: 1(there is a TSB on this code) defective thermostat. I know it's newer, but very possible it failed. The TSB also says the diagnostic software could be incorrectly displaying the code. And 2: the sensor in the expansion tank can give weird codes like this

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Thank you! I’m going to see if I can replicate it and check coolant temps to get a better sense of what’s going on.


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[PSUS4]

If it is a diagnostic software issue is that a dealer thing?


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