T6 Caravelle rear heater only blows cold air | Posts 16+

Hello Michael, when checking the heating support pump with VCDS in the actuator diagnosis, the message "-Rejected by the control unit-" appears with the code 7F 2F 7F. Best regards, Wolfgang.

Hello Wolfgang,

Then it probably won't be supported.

In this case, Rainer is definitely the better person to contact. He not only has VCDS software readily available, but he also has it installed in his T6. So, if anyone can give a definitive answer, it's the boss. Or another happy T6 owner here in the forum.

Then you should try to manually check the pump.
You should be able to feel if it's running. Or, if available, improvise a "stethoscope" by using a long screwdriver.

It is protected by fuse 29, located on fuse holder B next to the battery.

Best regards,

Michael.

Hi.

Unfortunately, I couldn't find any more pictures of that thing on my computer. However, images on the web clearly show that the coolant hoses connect directly to the heat exchanger.

The heat exchanger must therefore warm up at the latest when the engine is running. As far as I know, the auxiliary water pump is only for the auxiliary heater. I have the Climatic system. The Climatronic system is supposed to have an additional valve in the coolant hoses leading to the heat exchanger at the rear. According to the web, at least.
Did you properly secure the valve?

Best regards, Rainer.

Schmierpfote wrote:

Hello Michael, when checking the heating support pump with VCDS in the actuator diagnosis, the message "-Rejected by the control unit-" appears with the code 7F 2F 7F. Best regards, Wolfgang

This could be due to incorrect operation of the VCDS software. For example, it might be unable to log in to the control unit (ECU), the function might be called repeatedly, the ECU might be in an incorrect operating state, or the interface might be outdated and incompatible with the ECU.
hg
Herbert.

Hello forum, thank you for the help. Today, I have access to a lift, and the T6 will be inspected from underneath. Once the panels are removed, I'll be able to access the heater hoses for the rear heat exchanger. Best regards, Wolfgang.

Hello forum, I found the problem. The rear heat exchanger is clogged. I removed the underbody panel near the rear right wheel arch and measured the temperature on the supply and return lines. On a warmed-up T6, the supply line is 47 degrees and the return line is 13 degrees. Best regards, Wolfgang.

Hello Wolfgang,

Thank you for the feedback! How is that possible? Could there be a problem with the cylinder head, leading to a leak in the cooling system?

Best regards, Rainer.

Hello Rainer, the T6 has 170,000 km on the odometer and is 4 years and 4 months old. The AGR cooler was replaced free of charge. The clogging of the heat exchanger is supposedly due to coolant G 13. Greetings,
Wolfgang

Schmierpfote wrote:

Hello Rainer, the T6 has 170,000 km on it and is 4 years and 4 months old. The AGR cooler was replaced free of charge. The clogging of the heat exchanger is supposedly due to coolant G 13. Greetings Wolfgang

"Where does this statement originate, claiming that the cause is the coolant additive?"

Hello forum, a workshop manager hinted that the T6 model has these problems more often. There are also reports on YouTube about the G13. Best regards, Wolfgang.

So, it turns out there are indeed some irregularities. That's why I started this thread.
Okay, I'm ready. Please provide the German text you want me to translate.

vag-driver wrote:

So, there are indeed some anomalies. That's why I started this thread. /viewtopic.php?t=30875#249171

Bad, maybe replacing the coolant wouldn't be a bad idea...

"Hello everyone, I was at my parts supplier – a large company – and picked up some spare parts. I told the salesperson that I was returning the G13 coolant for my T6 because the heat exchanger is clogged, and I'll be taking G12++ instead. The salesperson said he was surprised I was buying G13, as there was a VW campaign advising against its use. However, there's no clear instruction, with some workshops using G12 and others using G13. Talking to salespeople at wholesale suppliers is better than any training at VW. 200 workshops that have to repair this mess after the warranty period know more than the poor VW mechanics." Best regards, Wolfgang.