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?

[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.

[ainarssems]

Check out this Link: http://www.audi-portal.com/en/diagnostic/ecu_12813.html

The bits that you are interested are measuring blocks about temperatures and fan activation, duty cycle as below:

Measured value block 132: Cooling
1)-
2)-
3)-
4)Status of cooling
(Meaning of 8-digit number block)
1 2 3 4 5 6 7 8
X No fault in system
X Thermostat actuator active
X Fan actuator active
X Control deviation (0 > specified temp; 1 < specified temp)
X Fan speed 2 active
X Fan speed 1 active
X Vacant
X Hot countries function encoded
(1=Condition met; 0=Condition not met)

Measured value block 133: Automatic fan detection
1)-
2)-
3)-
4)Status of cooling
(Meaning of 8-digit number block)
1 2 3 4 5 6 7 8
X Fan configuration plausible
X 0=Single fan; 1=Dual fan
X Fan configuration detected
X Vacant
X Vacant
X Vacant
X Vacant
X Vacant
(1=Condition met; 0=Condition not met)

Measured value block 134: Temperatures
1) Oil temperature [°C]
-60 - 195
Substitute value in case of defect: 195
2)Ambient temperature [°C]
-50 - 77
Substitute value in case of defect: 77,5
3) Intake air temperature [°C]
Ambient temperature - 110: Engine warmed up at standstill
Substitute value in case of defect: 20
4)Engine temperature combi [°C]
80 - 110: Engine warmed up

Measured value block 135: Fan actuator
1)-
2)Duty cycle fan actuator 1 [%]
0 - 100
3)Duty cycle fan actuator 2 [%]
0 - 100

Measured value block 136: Fan actuator
1)-
2)-
3)-
4)Fan run-on [Text: Off / Run-on]

Measured value block 137: Air conditioner requests
1)Air conditioner readiness [Text: AC-Low/AC-High]
2)AC compressor [Text: Compr. ON / Compr. OFF]
3)Pressure from air conditioner [bar]
0 - 40
4)Fan request from air conditioner [%]
0 - 100

Measured value block 138:
Thermostat diagnosis (no basic setting possible)
1)Engine start temperature [°C]
5 - 30
2)Mean engine air mass [g/s]
11 - 72
3)Mean vehicle speed [km/h]
35 - 120
4)Result [text: Test ON / Test OFF / Syst. OK / Syst. n.OK / Abort]
Syst. OK

Measured value block 139:
Thermostat diagnosis (no basic setting possible)
1)Engine temperature in diagnosis [°C]
> 76°C (specification for successful diagnosis)
2)Actual air mass integral [kg]
0 - 46
3)Specified air mass integral [kg]
10 - 14.2 (specification for successful diagnosis)
4)Result [text: Test ON / Test OFF / Syst. OK / Syst. n.OK / Abort]
Syst. OK

[Varrick]

Thanks again ainarssems, I'll pass this on. Hopefully will get to the bottom of it soon!

[HPsauce]

Definitely worth a call to our sponsors to see what they have and whether they can split the controller from the fan.