VW T4 AHY: Defective Auxiliary Heater / Parking Heater (Solution)

Hello, I own a VW T4 from 4/1999 with the AHY engine.

The Eberspächer D4WS water heater is installed from the factory. Recently, it has stopped heating. When turned on, the water circulation pump runs and warms the interior with residual engine heat, but nothing more.
The control panel of the standby heater isn't flashing either, which would normally indicate an error code. The standby heater's booster pump is receiving power on one cable, but not on the other. It should be cycling on and off.

When the pump is directly powered, it clicks briefly. The fuses related to the battery are all fine, the ones located to the left of the steering column compartment are all fine, and the ones under the driver's seat are all fine.
Reading the climate control system data reveals an intermittent fault with the fan motor. The error has been cleared/deleted. Bypassing the temperature sensor located under the towing hook with a test lamp also doesn't resolve the issue. Does anyone have any ideas?

Hello,

Reading the fault memory of the auxiliary heater... this can be done either with VCDS or directly with the Eberspächer tool. https://community.dieselschrauber.org/en/viewtopic.php?t=26145

Best regards, Rainer.

Rainer is an Eberspächer .
You can read this information using the EasyStartR+ remote control, if you have one.

Does the fuel pump at least make a sound for a short time at the beginning, or not at all?

Quote:

Rainer is an Eberspächer

.
Corrected.

Okay, I've made some progress now. I was able to read the display using a key combination. No errors were found, but the battery under the seat for the auxiliary heater had 0.74 volts. So, I replaced it. Now the ventilation system turns on, and various relays and pumps are working, but the fuel pump isn't ticking. Therefore, no fuel is reaching the engine.

Okay, so I expanded it, connected an external hose to the pump's suction line, filled it with fuel, and briefly energized it repeatedly. Nothing is coming out of the pressure line. Is this pump actually drawing fuel properly from the tank?
If I disconnect the fuel line, no fuel will leak out of the line.

The pump first draws in the fuel and then pushes it forward.
I would try taking it apart and cleaning the filter inside.

Hello Se6!

sebv6 wrote:

... The circulation pump for the underfloor heating is receiving power on one cable, but not on the other. ...

vs.

sebv6 wrote:

... the battery under the seat for the auxiliary heater had 0.74 volts. ...

With 0.74V at the second battery, the dosing pump could never have had any "power" either...
You should provide us with some more specific information, otherwise we will just be aimlessly searching around the area .
Describe, step by step, exactly what the auxiliary heater does after it has been turned on!
First, the burner fan and circulation pump must start up for a function test. Then, turn off the fan and turn on the glow plug; the latter can be detected by a voltage drop at the (secondary) battery. After approximately 10 seconds, the metering pump will THEN start to cycle.
Is everything as I described it?
For example, if a blockage or defect in the burner fan is detected, the process is stopped *before* that point, and the pump never receives power - intentionally.

"I would start by addressing that issue first, rather than disconnecting any hoses where it wouldn't matter if they were disconnected, especially if the dosing pump from the main system isn't being activated ."

By the way, there must be a reason why the second battery was so deeply discharged. We need to investigate and fix the problem!

Best regards from Munich!

sebv6 wrote:

The battery under the seat for the auxiliary heater had 0.74 volts.

Ah, the first, classic maintenance bottleneck .

RedR32 wrote:

sebv6 wrote: The battery under the seat for the auxiliary heater had 0.74 volts. Ah, the first, classic maintenance bottleneck

.

Good saying

Wenn der Temperaturschalter in der Gegend der Abschleppöse überbrückt ist, sollte die Heizung anlaufen, wenn der Motor läuft (Zuheizerfunktion). MacDid she do it?

This way, you can at least rule out dead batteries.

One thing I would definitely do with this auxiliary heater is replace the flame arrestor, if it's the type that can be replaced.
She must be around 20 years old.
And be sure to replace the heating element with a ceramic one.
With those two things, you've already addressed the main sources of problems with these auxiliary heaters.
"On my friend's D3WZ ACV, I only replaced the glow plug because the flame arrester is permanently integrated, and since then, she hasn't had any more starting problems, even though the flame arrester looks pretty bad."
Or if you're already at it, you might consider swapping it for a refurbished D5WS or D5WZ.
I find the D4 already too weak, especially since the two-way valve for short-circuiting the small heating circuit has been removed, which is how the motor helps with heating during the auxiliary heating operation.

Today, I finally had some time to dedicate to this topic.
Die Dosierpumpe habe ich erneuert und die 2. Battery.
After manually turning on the WSH, the fan inside it should start.
that blows air into the combustion chamber.

"But nothing is happening. I disassembled the J162 control unit and checked it for water damage."
checked, as well as all fuses, etc.

I think I need to expand the WSH (likely referring to a software or system) in order to test the fan.

Okay, after a long search: The error code indicated a faulty glow plug. I removed the heater and took it to the Bosch service center. They found that the control unit also had water damage and was defective. So, I got a new auxiliary heater, installed it. Unfortunately, it still didn't work. After a Saturday spent at the Bosch service center, where we searched together, I found a broken cable near the coolant manifold under the expansion tank. Now, finally, it's working! Conclusion: Glow plug: about 30 Euros, auxiliary heater: about 300 Euros, dosing pump: 80 Euros, labor at the Bosch service center: 100 Euros (business partner), battery under the seat: 80 Euros, gray hairs: 101.

Thank you for the feedback .