Spyerx

I completed the below steps, the issue is fan not turning on at 10oclock temperatures. I will be replacing the temperature sensor and then modifying it's trigger points with resistors wired in parallel.

The below steps did verify everything in the system is working other than the point at which the fans get triggered.

I hadn't seen an all encompassing 'test plan' so I compiled the below based on many good posts here. This should be pretty comprehensive. Took a couple hours to do everything...

• The below verifies:
• Wiring is good
• Temp sensor is good
• Ballast is good
• CCU is functioning to trigger fans
• Relays are good
• Fan is good / fan speed sensor is good

Test Plan:
Fan not turning on automatically

1. Read codes on CCU
2. Check fuse #2 30A fan cooler
3. Verify thermostat is opening by running car to temperature and feeling pipes to cooler
4. Remove relay #04, Check Low speed fan functions & ballast resistor functioning by jumping terminals 3(30) and 7(87c) for slow speed. Fan should run, even with the ignition off. If the fan runs in slow speed, your ballast resistor should be okay.
5. Jump terminals 3(30) and 5(87) for fast speed
6. Measure ballast resistor resistance .45 Ohm
7. Force fan to run on high speed, remove fender liner and unplug oil sensor wire, turn on car for 1-2 minutes, CCU should start the fan on high speed
8. Manually trigger CCU fan by putting resistance on oil temp sender circuit
   --Insert 600 Ohm resistor into temp pins with sensor unplugged to trigger low speed fan, turn on ignition
   --Insert 300 Ohm resistor into temp pins with sensor unplugged to trigger high speed fan, turn on ignition
9. Verify resistance of oil temperature sensor. Measure at CCU plug points listed below.
10. 13.6-19.6 K Ohm when at room temperature, sensor removed from system (will vary widely with room temp.).
    --3.6-4.0 K Ohm at 140f (sensor installed, across G12 & G18).
    --1.4-1.6 K Ohm at 185f (sensor installed, across G12 & G18).
    --0.9-1.0 K Ohm at 212f (sensor installed, across G12 & G18).
11. Check wiring to oil temp sensor by Checking G12 and G18 do not short to ground, unplug oil sensor & CCU first - Verified no shorts to ground
12. Check G18 is connected to ground when plug connected on oil sensor + ccu connected
13. Check G12 does not ground when oil sensor is connected
14. Check fan sensor circuit G9 does not short to ground, unplug fan & CCU first
15. Check G9 resistance against fan power terminals at fan motor connection with fan disconnected
16. Check G9 reads 12V when fan is running full speed (jump relay)
17. Ground K10 & K12 at the CCU to check the function of the relays and the wiring for the fan speeds. K10 = low, K22 = high
18. Verify relay fan output K10 (greed/red) Low Speed. Will read 12v when fan should be OFF. When fan turns to on should pull to Ground. 12v = off state, ground = on state.
19. Verify relay fan output K22 (brown/red) high Speed. Will read 12v when fan should be OFF. When fan turns to on should pull to Ground. 12v = off state, ground = on state.

My repair plan is replace the temp sensor and then modify for lower trigger temperatures.

ToreB

I guess you might have a failed oil cooler relay driver or two in the CCU. This problem can only be verified by doing measurements inside the CCU.
Cheers,
Tore

Spyerx

I checked one more thing.
I had some resistors laying around and connected them at the oil temp sensor for a ~1kohm measure at g12 and g18.
Fan is not turning on :-(
I will just do the g18 hack for manual switch

Question: if the ccu knows when I unplug the temp sensor and it switches fan on high... it seems that the high driver is working? Is it maybe the low that is not?

I will check the relay outputs voltage also per a previous post you made, tomorrow.

ToreB

CCU relay output driver problems are common and easily repaired.
It does indeed seem like the low fan speed output is shot.
Cheers,
Tore

Spyerx

UPDATE:
Connected everything back up
Removed oil temperature sensor
Suck a 1k ohm resistor in the plug (just stuck pins in). turn on car, no low speed
Tried 600 ohm, SUCCESS - I get low speed triggered
Put 300 ohm, SUCCESS - I get high speed triggered

SO: I believe my temp sensor is off/not working. I will replace it, I will also measure the trigger points and adjust resistance with a resistor in parallel to get the start points lowered a bit. I will also wire in a manual
high speed fan switch.

Spyerx

So I got a new oil temp sensor in
Also picked up a 1k ohm potentiometer.
I attached a thermocouple to the sensor to map out the resistance as it heats up.
About 210f it's 1k ohm
It doesn't hit 600 ohm until about 235f
This is when my car triggers the low fan (I will validate this with the potentiometer)
Added a 2.2k ohm resistor in parallel and at 215 or so it hits 600 ohm

So this should be perfect to lower the threshold to trigger the fan.

Will post results on the car once done messing around. Raining here so get to play with silly little projects.

Spyerx

After determining that my fan/ccu/relay system is working correctly, I got a chance to do some testing and update my car with the lower temp mod. As has been posted here before, here are some numbers.

Test method: heat gun with a thermocouple zip tied to the brass sensor. Not perfect, but, did test several times heating up and cooling down to get these numbers. This is a brand new porsche sensor out of the car.

Temp - Resistance - Resistance with 2.2k ohm 1/2 watt resistor in parallel
75f - 19k ohm
100f - 9k ohm - 1.78k ohm
125f - 6k ohm - 1.55k ohm
150f - 4k ohm - 1.30 ohm
175f - 2.5k ohm - 1.08k ohm
200f - 1.4k ohm - 800 ohm
212f - 1020 ohm - 640 ohm
225f - 865 ohm - 580 ohm
250f - 680 ohm - 500 ohm

Next, I got a 1k ohm 1/2 watt potentiometer (variable resistor from 1k ohm to 0 ohm). I soldered 2 leads onto the middle and one side of the variable resistor. I then connected the leads to the oil temp sensor plug. Turn the car on (starting not needed), and set the pot to 1k ohm (fully "open").

I turned the potentiometer to find the below resistance points:
Fan turns low to off: 808 ohm
Fan starts low: 680 ohm
Fan starts high: 565 ohm
Fan turns high to low: 696 ohm

As you can see, in stock configuration the fan won't start low until nearly 250f !?!?! Now, I'm not sure why, component drift with age? Not sure, but, with the mod, the fan now starts low right around 215-220. It will switch to high around 240f. This explains why I have never heard my fan come on, even though electrically the entire system is working.

The simple mod that's been posted to wire in a 2.2k ohm 1/2 watt (1/4 would be fine I think) resistor in parallel at the oil cooler temp sensor is a good fix, so thanks to the OP who posted that a while back.

Confirmed testing in car:
Fan low speed turns on just a bit below 9 o'clock on the gauge
Within a few minutes the temperature drops to about a needle width below the 3rd line (8 o'clock)
The fan shuts off
And it cycles like this.
I can't get it hot enough now idling to trigger high speed fan!
Before this I could easily get temp to 10 o'clock.

If anyone is in SoCal and wants to test out my little test rig, let me know, super easy to do and debug your cooling fan.

Why do I care? Track use, stop and go traffic. I'm also going to wire in a dash switch to trigger the high speed fan on demand.

Hope this is helpful for people

dlpalumbo

I think, if you have A/C, that when switched on both fans should run. So you might not need the additional switch.

Spyerx

I will check again but I believe this has been shown to not be the case.

02m2

I will drop off my car..what time is good for you..lol

Spyerx

haha... get it back first :-)

Easy to see if fan is working right you do want the low speed if you are using as a daily around here, stop and go with AC on...

02m2

Sent the CCU out to the guys in FL for the mod. Should have it back late this week or early next.

Spyerx

what mod?

apanossi

+1 I did this simple 2.2k ohm mod last year and it works a treat. My temp never goes above 9 o'clock, even during my 1-hr daily commute in LA traffic.