I have a 2007 Passat 2.0T with a CEL. Here's the description of the code + freeze frame info:
1 Fault Found:
008577 - Performance Malfunction in Cooling System
P2181 - 008 - Implausible Signal - MIL ON
Fault Status: 11101000
Fault Priority: 0
Fault Frequency: 1
Mileage: 105914 km
Time Indication: 0
RPM: 2081 /min
Load: 61.9 %
Speed: 104.0 km/h
Absolute Pres.: 1000.0 mbar
Voltage: 14.097 V
I have searched here and on GIS, and found conflicting information. I did the AC on while cabin fan set to 1 test, and found both radiator fans not turning on. I ran the engine for a while and both fans come on during high speed. I also tried clearing out the code thinking having the AC on could cause the error code (since it's getting quite chilly nowdays), but the light came back on after a couple of days.
I'm leaning towards the fan control module, but some posting indicates that it's a separate module, while others claim that it's built into the fan assembly. Some posts suggest CTS (Temperature sensor), but I haven't found any link between CTS and the low speed fan mode. Also, there's a talk about there being two CTSs in the car, one near the firewall, and under the car.
Is there anyone here who can help me figure out what could cause the low speed fans not to kick in when AC is on, and if it's ever related to P2181 code? I have one CTS ordered as it's the easiest part to replace, but I have a feeling that it might not be the root of the problem. Could thermostat cause low speed fan not to kick in? The car doesn't overheat, nor the freeze frame indicate any temperature issue (and I've also verified that the high speed fans kick in). Also, is there a relay that controls the low speed fans?
Thanks in advance!