T6 Caravelle rear heater only blows cold air

Hello forum, my T6 is only blowing cold air from the rear heater vents. I ran a diagnostic scan with VCDS. The servo motor is defective. The connecting rod for the temperature flap has come loose, and the flap is currently secured with wire at the bottom position. I took it for a test drive, and it's still only blowing cold air. Even when I fixed the flap to the top position, it still only blows cold air. Does anyone have any ideas on how I can get heat to the rear of the car without having to replace anything? I will use VCDS to perform the basic settings for the new stepper motor.
I would be grateful for any help. Best regards, Wolfgang.

Good evening, Wolfgang.

The actuator motor has a short circuit to the positive terminal. Okay, heading towards the climate control unit.

You can adjust the settings mechanically at the back of the control panel as much as you like, but the electronics won't register those changes.

You will need to replace the servo motor in order for the temperature control to function again.

In addition to the issues with the battery management system, you also have an error in the auxiliary heating system.

There may be a causal relationship here. If the bus error is caused by the potentiometer.

Clear errors, check what remains.

Can you replace it?

Check the auxiliary heater.


Does the auxiliary heater support the main heating system?


Best regards,

Michael.

Thanks, Michael, for your help. I was thinking that if the servo motor stops working, it might still be possible to fix the flap manually and get the heating working again in the back. Normally, the heat exchanger in the heating system has the same temperature as the coolant, and the valve either allows warm air to enter or prevents it.
Does the control unit prevent water flow by switching off an auxiliary water pump for the rear circuit, or are any valves closed? Best regards, Wolfgang.

Hello Wolfgang,

Perhaps I haven't fully understood your problem.

Therefore, I'll ask in a different way:

1) In principle, air enters from the front and the back?

2) Is the air warm in the front and only cold in the back?

Is the auxiliary heater running?

Does the heating output and airflow generally match the specifications?

If there's no airflow from the back, there's another option.
Alternative.

The auxiliary heater supports the heating output. However, an error is registered: coolant temperature -48 degrees. This error message is implausible and could potentially prevent the auxiliary heater from starting (without displaying an error). If the auxiliary heater is not working correctly, the rear area will warm up slowly or insufficiently (in cold temperatures).

Your climate control unit regulates the air temperature and intensity. A short circuit, specifically a positive voltage surge, can cause the control unit to malfunction temporarily. The potentiometer is also a temperature regulator.

(I experienced limitations in the heating performance of the air conditioning system in a Touran, which was also caused by a defective potentiometer.)

Therefore, clear any errors, test the climate control and auxiliary heater, and replace the temperature regulator.


I hope I understood correctly? Otherwise, you would have to explain your problem to me again, but in a different way.


Best regards,

Michael.

Schmierpfote wrote:

Normally, the heat exchanger in the heating system has the same temperature as the coolant, and the valve allows warm air in or not.

Since this concerns the heating output, it's as you wrote. Is the heat exchanger or the supply line possibly blocked?

Hello,

In the T6, there is a heat exchanger located on the right-hand side at the rear, which is connected to the cooling circuit via two hoses.
And also, a blower.
It can either heat up, or it won't.
If the fan is running and the coolant valve is open, it should also get warm.
The coolant hoses are easy to access, and if nothing gets warm in any valve position, it's likely either a blockage or the valve isn't opening properly.

Best regards, Rainer.

Schmierpfote wrote:

The connecting rod for the temperature flap has come loose, and the flap is secured with wire to the lower stop. (...) When the flap is fixed to the upper stop, it only allows cold air to pass.

I suspect you fiddled with the wrong valve.
Please describe in more detail what was done where.

Thank you for the responses. I just replaced the rear temperature control motor, cleared the error codes with VCDS, and performed the basic settings with VCDS. I ran a scan, and there are no errors. However, only cold air is coming out from the rear. The temperature control flap is located at the rear, under the heater fan, and the air distribution flap is located above the heater fan. I can't access the heater hoses for the rear heat exchanger without removing the trim. Is there an auxiliary water pump for the rear heat exchanger? Where can I find the heater valve for the rear? I thought the desired temperature was achieved through the damper control system, not through valves in the water circulation system.
Best regards, Wolfgang.

Hello forum, is it possible to test the outlet temperature sensor located at the rear -G174- using VCDS? Perhaps it's providing incorrect values. Best regards, Wolfgang.

Hello Wolfgang,

Once the bugs are fixed, there probably isn't much else to do.

Is the error in control unit 18 resolved, and is the auxiliary heater working? Is the V55 auxiliary water pump running?

Is there possibly a switch in the car to disable the auxiliary heater?

Were any other maintenance tasks performed? Specifically, regarding the cooling system? Is there air in the system, or was coolant added that could potentially clog the lines?

You might be able to check the parameters with VCDS before you remove the side panel.

You should be able to read the temperature sensor G174 from the measured values. This is where you can see if it's providing realistic readings. However, 12.3 isn't entirely unrealistic... If you set the heating to the highest setting, you would still expect noticeably warmer air to come out.

I'm spontaneously observing a discrepancy between the actual and target blower voltage at the rear. And setpoint/actual temperature control flap at the rear.

Did the pairing process work, and was the information correctly transferred?


Best regards,

Michael.

Hello Michael, the ZH (central heating unit) has been converted to an SH (auxiliary heating unit) and is working perfectly with the timer and remote control. I have reset the position of the control motors for the flaps at the front and rear using VCDS. The water pump for the ZH is running, otherwise the ZH would lock. I need to find out if the T6 still has an additional water pump for the rear heat exchanger and test it. The T6 was manufactured in December 2017 and had the EGR cooler replaced under warranty. The rear heater fan is blowing a lot of cold air into the interior. I have adjusted the flaps using VCDS, and they are moving. Best regards, Wolfgang.

Hello Wolfgang,

I suspected that there would be renovations.

Okay, the V55 is running. And that switch doesn't exist.

Next up is the V 488 auxiliary water pump. It's located at the front, near the pump for the EGR cooling system.

5Q0 965 561 B




Best regards,

Michael.

Thanks, Michael. Can I check the V488 using VCDS? I only found the "heating support pump" but the test wasn't executed. Best regards, Wolfgang.

Hello Wolfgang,

The V 488 is the heating support pump. If listed, an actuator test should be possible using VCDS.

If it doesn't run, check the extended measurements to see if the pump is listed. Here, the On/Off status should be displayed.




Best regards,

Michael.

Thanks, Michael. I'll do it over the weekend and buy a new one beforehand. I'll get back to you. Best regards, Wolfgang.

Good evening, Wolfgang.

Since the taxi only generates revenue when it's in operation, I'll provide the part numbers for the last two common mechanical components that are prone to failure. While there are still check valves in the system, I've never had to replace one.

The thermostat shut-off valve, part number 7E0 820 295 B, is the Y-piece located near the auxiliary heater. If it's accessible, you could check if all three hoses are equally warm. If the return line is colder than the other two, the thermostat is likely defective.

If all three are equally warm, then the second auxiliary water pump probably also works.

Then, the troubleshooting starts at the back of the 2. Heat exchanger continue.

7H0 819 032


Okay, please provide the German text you want me to translate. I will translate it and provide only the English translation, without any explanations. I will also check the translation for accuracy and fluency.



Best regards,

Michael.