RomRaider

Hi everybody,

I know this has been raised a few times and is typically caused by bad grounds / ground loops. However my problem is a bit different as you will see, maybe somebody already experienced the same behavior and has a solution.

My setup works absolutely fine with my other cars. This E46 track build also reads fine, no matter if the engine is running or not - until the cooling fan turns on.. When the fan is spinnig I'm getting huge amount of noise that ruins communication.

I added the pin for fan pwm to my bench setup and hooked the whole thing to a high quality 1600W PSU. When I turn the fan on with INPA I get ~3Vpp ~49kHz ripple on the 12V line and ~2.5Vpp on pwm drive which is probably also present on K-line causing my problem. The frequency seems static no matter how fast the blower spins, so I think it's not brushed dc motor noise but maybe the final pwm drive from the blower controller. I've tested two different blowers and two different drivers with the same result, so I think this works just like that from factory and the noise should be suppressed somewhere else.

Can a faulty voltage regulator cause that? Should it also handle this kind of ripple added by an aux component?

Thanks in advance

I hooked up my scope today - CH1 is the engine compartment battery terminal, CH2 is K-Line from diag connector.

Idling without fan


Idling with the fan on


Idling with fan on and a bit of load applied (cabin blower on max setting, interior lights, rear running lights)