Strange CCU Issue...Opinions?

LA964RS · 06-19-2007, 02:17 AM

I went through and read what threads I could find on this subject and this scenario sounds different than the ones I found.

My buddies '92 had the battery go dead recently...first time ever. Then he had the car kick a CEL. I went over to check it out and I reset the CEL and it didn't go back on when car restarted...but seems like the little fan motor in the CCU was just running....with the ignition off, key out! I'm like what's that noise...and it smelled like...you know that smell before smokes starts coming out of the dash?...Yeah, like that!

Anyway, pulled the battery neg again and let it sit for a bit. Hooked battery back up and no fan running....

So is this the sign that the v.expensive CCU is about to take a sh*t????

All the other functions of the CCU work fine....car is what 15 years old now...how long these units supposed to last?

Thanks.

Megatron-UK · 06-19-2007, 04:42 AM

Doesn't the fan run on for a bit when you switch off anyway? I'm sure I read that on here somewhere...

John52 · 06-19-2007, 09:46 AM

There are a lot of documented problems with the CCU fan. I can only share my experience. Yes, the fan is supposed to stay running for 15 to 30 seconds after the ignition is shut off. However, in my case, it just kept on running until it killed the battery after a few days. All other CCU functions worked fine.

Given the price of a new CCU (big bucks) my mechanic opted to install a simple relay switch between the ignition and the CCU. When the ignition is on, power is provided to the CCU, when ignition off , no power to the unit , so the fan doesn't run.

dfinnegan · 06-19-2007, 10:06 AM

That fan will run for up to 20 mins after shutting the car off. Come back after 20 mins and if it's still running then there is a problem.

LA964RS · 06-19-2007, 12:12 PM

20 minutes! I've had a 964 for 7 years now and its never run that long....wonder if mine is working?

I think my buddy needs the fan issue resolved as I bet that's what drained his battery...

All great info, thanks.

JasonAndreas · 06-19-2007, 05:07 PM

Quote:

Originally Posted by John52

Yes, the fan is supposed to stay running for 15 to 30 seconds after the ignition is shut off. However, in my case, it just kept on running until it killed the battery after a few days.

If the fan is staying on for longer than 20 minutes and draining the battery the proper fix is to replace the transistor (T1) BC337 ($0.36USD) on the lower PCB. Unfortunately I don't know of any method to test the transistor without first removing it? Anyone here an EE?

Wick up the solder

Remove the component and clean the PCB with denatured alcohol

and don't use this much solder.

and then clean again after its cooled.

I had to temporarily remove the component next to the transistor to place it properly. My only other option was to split the two circuit boards and that involves soldering a bunch of joints versus only two.

06-19-2007, 02:17 AM	#1
LA964RS Addict Rennlist Member Join Date: Sep 2004 Posts: 2,299	Strange CCU Issue...Opinions? I went through and read what threads I could find on this subject and this scenario sounds different than the ones I found. My buddies '92 had the battery go dead recently...first time ever. Then he had the car kick a CEL. I went over to check it out and I reset the CEL and it didn't go back on when car restarted...but seems like the little fan motor in the CCU was just running....with the ignition off, key out! I'm like what's that noise...and it smelled like...you know that smell before smokes starts coming out of the dash?...Yeah, like that! Anyway, pulled the battery neg again and let it sit for a bit. Hooked battery back up and no fan running.... So is this the sign that the v.expensive CCU is about to take a sh*t???? All the other functions of the CCU work fine....car is what 15 years old now...how long these units supposed to last? Thanks.

06-19-2007, 10:06 AM	#4
dfinnegan Addict Rennlist Member Join Date: Jul 2005 Location: NY, USA Posts: 3,294	That fan will run for up to 20 mins after shutting the car off. Come back after 20 mins and if it's still running then there is a problem. __________________ 1991 C4 Coupe, Polar Silver The hours a Porsche spends parked. You don't get those back.

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06-19-2007, 04:42 AM	#2
Megatron-UK User Join Date: Jul 2006 Location: North-east England, United Kingdom Posts: 875	Doesn't the fan run on for a bit when you switch off anyway? I'm sure I read that on here somewhere...

06-19-2007, 09:46 AM	#3
John52 User Join Date: Sep 2001 Location: Ontario, Canada Posts: 119	There are a lot of documented problems with the CCU fan. I can only share my experience. Yes, the fan is supposed to stay running for 15 to 30 seconds after the ignition is shut off. However, in my case, it just kept on running until it killed the battery after a few days. All other CCU functions worked fine. Given the price of a new CCU (big bucks) my mechanic opted to install a simple relay switch between the ignition and the CCU. When the ignition is on, power is provided to the CCU, when ignition off , no power to the unit , so the fan doesn't run.

06-19-2007, 12:12 PM	#5
LA964RS Addict Rennlist Member Join Date: Sep 2004 Posts: 2,299	20 minutes! I've had a 964 for 7 years now and its never run that long....wonder if mine is working? I think my buddy needs the fan issue resolved as I bet that's what drained his battery... All great info, thanks.