Hi all,

I wonder if someone could be kind enough to educate me on the workings of the auxiliary heater that kicks in to heat up the hot air blowers?

It was not been switching on yesterday and the air was mildly warm as you can imagine. I thought perhaps we had a problem with it and was going to get it checked out tomorrow.

However, when I filled up with diesel tonight it came straight on and working fine.

Is the diesel level relevant to it working?

 

Dunno about the 2005 but on my 2002 the Aux heater does only heat up the coolant for the engine (so indirectly adds to the cabin heating)
And needs following conditions to start:
From the RG manual:

For vehicle’s with a Manual Temperature Control
system, the DCHA will activate only:
² when the engine is running.
² when the coolant temperature is below 66°C
(151°F).
² when the fuel tank has greater than 1/8 of a tank
of fuel.
² when the Power switch on the A/C - Heater
Control Module is on.
² when the Blend control on the A/C - Heater
Control Module is set above 90% reheat (within 2
detents of the full heat position).
² once per ignition cycle, when the ambient temperature
is below 9°C (49°F), and the vehicle
speed is above 25 km/h (15.5 mph) for two minutes,
and the Blend control on the A/C - Heater
Control Module is set anywhere from 80% to 90%
reheat (3 to 4 detents from the full heat position).
Under this circumstance, the DCHA will remain
active for five minutes unless additional input is
supplied to the DCHA.
² when the Front Control Module (FCM) sees the
Cabin Heater Activation request that is bussed
from the A/C - Heater Control Module.

For vehicle’s with a Automatic Temperature Control
system, the DCHA will activate only when the:
² VIN indicates that the vehicle has a diesel engine
² vehicle’s odometer reads more than 5 miles.
² engine speed is above 500 rpm.
² coolant temperature is below 66°C (151°F).
² fuel tank has greater than 1/8 of a tank of fuel.
² Power switch on the Automatic Temperature
Control is on.
² Driver Temperature Control on the Automatic
Temperature Control is set above 22°C (72°F).
² Front Control Module (FCM) sees the Cabin
Heater Activation request that is bussed from the
Automatic Temperature Control.

 

Yes, needs a minimum or it will not switch on the AUX in order to protect the main engine. It heats water !

 

Merl & Vmaxxer,

A standard diesel has up to 0.2 ml of water per litre, about a third is dissolved in the fuel the remainder sits in the bottom of your tank. Microbes can't grow in diesel but do grow and multiply in water [needs100 ppm] these organisms are ok when they are suspended in fuel before fuel reaches the engine causing blockages to filters which after all are primarily designed to remove inorganic debris from the fluid stream not organic material. Add to that wax crystallization, organic debris and other things hiding in the last dregs of a tank and filers generally are not enough to cope.

Merl, I carry an 11 litre jerrycan and if ever my warning light came on and I couldn't get to a filling station in 10 or so miles I would fill up.. I would never say oh! its ok I'll do it tomorrow, knowing what $****e is being sucked up into my expensive HP pump & injectors. Vmaxxer, maybe the previous owner of yours was constantly running short time an time again and the EEPROM in the Webasto decided it had a fault with the frequency of the 'no start' error and shut itself down to protect itself. The owner [maybe] pulled the plug on it thinking it was broken when in fact it was just doing what it should do - protect itself and the occupants of the vehicle.

 

The Webasto did the right thing to go in "shutdown" because in my case the fuel line from the tank to the Webasto was disconnected, ripped of the outlet on the tank. No way it could start and probably couldn't start for a long time.

My problem was getting the DCHA out of its hibernation state, and it finally worked by disconnecting the #15 fuse for a while.
I will keep on checking the heater if it keeps working.

 

Hopefully it will my friend, yes all EEPROMS can suffer from legacy errors [crap codes almost impossible to shift], without diagnostics there's no way to even read them let alone manipulate them. For example the air-top's usually have an adjustable temp [day-travel / night-needs] digital control with a very limited set of error codes that a user can actually see, not so the thermo-top.

What you did was interesting you shocked the EEPROM to reboot its source code for a full manufacturer reset. In the same way that all computer MOBO's have a J1 for a reset but when legacy codes stop the 'clean boot' reset one trick is to pull the CPU / memory / video card right out so the logic thinks its lost an essential limb - it then shocks itself into a reboot it would not previously give you. No matter so long as it works for you my friend !

 

sub NOTE :

- makes sense the LOGIC on the car side [not the Webasto] needs 15 or so minutes to shut down and log its 'current state'
- it does not as many believe happen instantly, its still looking for a radio or interior lights left on long after the IGN key is pulled
- when later you then switch on and start the car the EEPROM compares 'old current state' with 'new current state' for issues
- going back to the MOBO analogy it now knows it needs to supply a voltage to the Webasto because it sees it as an essential limb

> as an aside <

A Webasto will pull a massive 17a for about 3 minutes on both the boot up and boot down cycle. It uses a glow plug to boot up and a glow plug to burn the surplus [already pumped] fuel from the swirl bowl out of the exhaust before switching off.

From the workshop manual Automatic Temperature Control system, the DCHA will activate only when the:

• VIN indicates that the vehicle has a diesel engine
• vehicle’s odometer reads more than 5 miles.
• engine speed is above 500 rpm.
• coolant temperature is below 66°C (151°F).
• fuel tank has greater than 1/8 of a tank of fuel.
• Power switch on the Automatic Temperature Control is on.
• Driver Temperature Control on the Automatic Temperature Control is set above 22°C (72°F).
• Front Control Module (FCM) sees the Cabin Heater Activation request that is bussed from the Automatic Temperature Control.

When the DCHA starting sequence begins, a DCHA active telltale illuminates in the instrument cluster and the glow plug and the combustion air fan are activated. After 30 seconds, the fuel dosing pump begins operating and the combustion air fan operation is suspended for 3 seconds. Subsequently, the combustion air fan speed is increased in two ramps within 56 seconds to nearly full load operation. After a stabilization phase of 15 seconds, the combustion air fan speed is again increased in a ramp within 50 seconds to nearly full load. After reaching full load fuel delivery, the glow plug is deactivated and the combustion air fan operation is increased to full load.

During the subsequent 45 seconds, as well as in normal operation, the glow plug functions as a flame sensor to monitor the flame condition. After all these events, the automatically controlled heating operation starts. In case of a no flame or a flame out condition, a restart is automatically initiated. If the no flame condition persists, fuel delivery is stopped and the heater enters an error lockout mode with a rundown of the combustion air fan. This will set one or more DTCs in the DCHA Control’s memory. If six continuous attempts to start the heater fail due to one or more faults in the DCHA system, the heater enters a heater lockout mode. This will set DTC B1813 along with any other fault(s) that the DCHA Control identified.