Happily motoring along top-down on a perfectly cloudless 66° day, the a/c fan kicked into high gear for no reason. After pumping the temp up to 76° with no effect I just turned the climate control off.... only to notice the CEL was illuminated. Using Torque I found these two codes. Cleared them. No other symptoms other than climate control in manual or auto isn't generating heat. After clearing the codes, still no change. I can see where a new thermostat may be in order, but the U0405 is puzzling. Thoughts?? Codes have not popped back up after a two hour journey post-clearing.

 

P0128 is a generic code and by law needs 2 engine warm ups (minimum) to flag.

 

U0405: Invalid data received from speed control module
That could be nothing more than a transient out-of-range signal.


P0128: Coolant Thermostat (Coolant temperature below thermostat regulating temperature.
The Workshop Manual gives possible causes as:
1. Low/contaminated coolant
2. Thermostat
3. Cooling fan circuit(s)/module

Graham

 

P0128, probably the thermostat. The rubber gasket stretches and ends up blocking the thermostat from closing, so it takes longer than normal to get the coolant up to the expected temperature during startup.

 

kj07xk and
GGG


Thank you! Have appt at dealer for thermostat... $58 for the part......