Advice needed - Jet powered coolant fan!

[Varrick]

Hi all,

New member of this great community!

I have a 2003 D3 4.2 petrol which I have had now for a few months, but without it's problems, and very grateful for advice to help the old girl get back on her feet!

Battery - appears to be a drain, 10% battery indicator on MMI, starts up ok, but convenience functions such as central locking appear not to work, until after the car has been running. Lock the car via remote, go back to it after 10 mins same thing again.

Coolant fan 2, start the car up from cold 10 seconds later, sounds like a 747 on take off, with larger (not AC fan) on full chat, continues even when engine switched off, drained the battery very quickly so had to pull the connection to stop it. AC fan cooling fan works fine, activating / deactivating with AC on and off as expected.
Hooked up to VCDS and reports 18308 - Coolant Fan Control 2 P1900 - 004 - Open or short to ground. initially thought may be control unit integrated into fan, but tested by independent state ok, and that think the problem is somewhere else up the circuit.

Other issues which may or may not be related are no siren when alarm goes off, advanced key not working, electrical steering column adjustment not working.

Apart from that all good!

Any advice or guidance greatly appreciated, as is a copy of a wiring diagram to help diagnose the coolant fan fault?

Thanks in advance guys!

Varrick

[Architex_mA8tey]

Welcome to the forum

On the battery, it is common for the battery control module to gain problems and then cease to function as well as it should, so the options are either to replace the module or what you can do temporarily is fool the system into thinking you've fitted another battery by changing the current battery coding. If the car has plenty of charge in the battery then this action will mean all of the convenience functions will return and work for at least a while!

Wiring diagrams are all on this document HERE

[Varrick]

A_m - thanks for the information, in your experience is it worth trying to source a replacement module or how effective is it worth trying to fool the system?

Any idea on the excessive fan noise as it driving me bonkers! Or should I spend more time at Gatwick and get used to the noise in the longer term?

[Architex_mA8tey]

Originally Posted by Varrick

A_m - thanks for the information, in your experience is it worth trying to source a replacement module or how effective is it worth trying to fool the system?

I would try to fool the system first and see how long that lasts before you get into the same position. If it is weeks rather than months then it is probably worth changing the module

[Varrick]

Thanks everyone, she's still on the ramps but will keep you posted on the results!

[Varrick]

Hi everyone, thought I would provide an update. Pleased to say that all problems now fixed, courtesy of juice from a new Bosch Silver and a replacement coolant fan / control unit purchased from the forum sponsors! I must say the service provided by Maria at Prestige was fantastic! Good work!

[ainarssems]

ECU sends PWM signal to fan control unit depending on the fan speed required. If the fan is constantly on either control unit is faulty or ECU requests fan to be on possibly because of wrong temperature reading.

[Varrick]

Thanks fella's, assume this may point in the direction of the thermal switch / coolant sensor?

[ainarssems]

Considering you have fault code 18308 - Coolant Fan Control 2 P1900 - 004 - Open or short to ground I would be more inclined to believe it's the fan control units fault, they do fail occasionally, unfortunately they come together with fan and dealer does not sell them on their own. Check the temperature readings in VCDS if they all seem OK it will probably be the fan control unit. You might also be able to check fan duty cycle in measuring blocks in VCDS.

[Varrick]

ainarssems - thanks, will take.your advice and check this out again! Thanks again to everyone concerned for your help, great forum.