Heating system fault 38 (unknown)

[thormann]

Hi,

when reading the fault memory of the heating/aircon (system H01), Durametric gives me an unknown fault 38. I can erase the fault, however it always returns.

Going through the 2000 workshop manual, the last fault code is 32.

Any idea, what to do?

Thanks,

Gert

[tholyoak]

Sounds like you have the wrong HVAC controller. Fault 38 is the CAN bus timeout on the CAN comfort circuit (instrument cluster, HVAC, PCM/CR23).

-Todd

Edited April 30, 2008 by tholyoak

[thormann]

Thanks! If this is a CAN timeout, then it is probably because of the CDR23, that I removed for an aftermarket unit!

Can I fix it somehow?

[thormann]

In the 2000 wiring, the CAN comfort did just connect the cluster and the A/C, the radio got analogue signals ! How was the CDR 23 integrated in the CAN comfort? Can I just short circuit the high and low terminals of the plug if it is a CAN ring? Unfortunaltey I do not have a 2003 wiring!

[tholyoak]

I guess since you are in Europe the model years may differ slightly. In the US the 2002 model did not have a CAN bus to the comfort network and used a different HVAC controller. The 2003-on model used a CAN comfort bus to the PCM/CDR23 and uses a different HVAC controller. Prior to 2001 there was no CAN comfort or DME bus only a CAN bus for the Tiptronic. If you removed the CDR23 this is why you have the error. It doesn't affect the functioning of anything and is a harmless error as far as I can tell.

-Todd

[thormann]

Does anybody know, which information are shared in the comfort can between cluster, HVAC and radio?

I think speed and illumination is required for the radio. But what is required for the HVAC, for instance? only illumination ?

Since I have removed the radio, the CAN Ring is interrupted and probably not any information is shared anymore, even between cluster and HVAC.

Edited July 7, 2008 by thormann

[tholyoak]

Actually on 2003 and later vehicles the CDR23/PCM is also connected to the CAN comfort Bus that includes the Radio, cluster and HVAC.

The CAN comfort bus for the radio is used primarily to display the track/station info in the cluster center OBC display but has other functions as listed below

The comfort bus transmits:

A/C request from HVAC controller to the cluster then to the DME via the engine CAN bus

K-lead (diagnosis), allows diagnosis of the controllers via OBDII port

Instrument cluster information (ie vehicle speed for speed dependent volume)

Sun sensor, connected to instrument cluster and used in auto illumination of the controllers connected to the bus as well as regulate the fully automatic climate control. The former function is used in conjunction with the photodiode signal on the front of the CDR23/PCM unit.

-Todd

[thormann]

Hi and thanks for answer.

As far as I read the wiring diagram the can comfort is arranged as a ring collecting cluster, hvac and radio (each high an low). Since I have removed the radio, there is a gap in the ring and I doubt, that the remaining units (cluster and hvac) are still communicating. That means, I have lost some features such as automatic climate control with sun sensor? Or am I wrong and the HVAC and the cluster are still communicating even without the gap?

Marco

Edited July 8, 2008 by thormann

[Loren]

I think you might get around this but programming MOST and telling it there is no radio.

[tholyoak]

It really isn't a ring, the cluster acts as a hub for the can comfort and can dme. The CDR/PCM can comfort wires hook into the CAN wires from the HVAC controller, so radio removal doesn't have an effect, other than an error in controller fault memory as it is missing. As Loren suggests you can program the car with the PST such that it is coded without PCM/CDR23. This is how 2002 models are coded as they didn't have the CDR 23 until 2003 but use all of the same controllers, with the exception of the climate control, but I know from personal experience that the 2003 HVAC controller will work in a 2002 coded setup.

-Todd

[thormann]

Thanks for this detailed answer. That was exactly, what I wanted to know.

If the cluster is the "hub", then the radio is hooked up there too, I guess! The error is no problem for me then!

Maybe later I will have it programmed!