I have an '03 Golf GL, and my Check Engine light has been on for a while. I finally picked up an Actron CP9180 AutoScanner, and read the code: P2181, which is described as "Cooling system performance". From what I can tell, though, everything is working fine:
- Both radiator fans turn on and seem to run fine (it's cold, so I had to turn on the AC, which meant I had to wait until it was at least 40F out)
- The dashboard temperature gauge warms up to 190F and locks there (yes, I know it's designed to lie, but it's at least doing what it's designed to do)
- The coolant temperatures read by the Actron go up to about 174 when the dashboard hits 190, and then stay between 175 and 205
- Although I'm not certain, I think I've found the engine temperature sensor, and it's green (which is reputed to be "good").
I tried clearing the engine code, but a few days later it came back (while driving on the highway). I've gotta get this inspected, so I need to solve it.
I don't think it's the temperature sensor(s), since both the dash and engine computer temperatures seem to be working. I don't think it's the fans (unless there's an issue with the fan speed being wrong). I don't think it's the thermostat, since the coolant temperature seems reasonable. I don't think it's the water pump, since again the coolant temperature seems reasonable. Add all this together, and the problem doesn't exist... but it does...
Any ideas? Anything else I can look into before I hand it to the dealer (which would be a royal pain in the wazoo)?