The cabin fans have been suffering from spark errosion on the motor interior contacts.
The burning that occurs between the motor brushes and the commutator increases resistance
to the point that the electricity can no longer flow into the motor, this obviously stops it working.
Click here for a fix.
This is the newest failure of the 451 heater setup. The temperature sensor inside the heater box fails.
This creates the same error as having low AC gas (AC light comes on but compressor doesn't engage).
The sensor measures the temperature of the air to ensure it's worth putting the AC on at all.
The smart doesn't activate the AC when the air temperature is very low. Unfortunately,
disconnecting or having a faulty sensor makes the car believe it's about -40 degrees outside.
Click here to check and fix the fault.
This fault is as old as the car itself and started to appear only months from the 451 being released.
As you adjust the heater selector, you either get cold or maximum heat.
We initially believed that something on the controller PCB failed, like a chip, solder joint or sensor.
What we didn't realise was how clever (or stupid) these control units were.
It would have made sense to hard code the position of the heater selector. Oh no!
The unit attempts to accurately control the climate of the car by automatically adjusting the cabin heater flap
to mix hot and cold air to reach the desired temperature selected. The problem is that the controller learns
a bad habit and its control over the heater flap become erratic. So you only tend to get hot or cold.
Initially, smart would replace the entire unit but further inspection allowed them to recode and recalibrate
it from the OBD port. It is believed that the new coding will stop the problem happening again. We'll see.
[the heater controller] monitors two cabin temperatures, one by an infrared sensor, second by the thermistor probe in the A.C. plenum found on the left side of the right hand foot well. To calibrate this system, an infrared temperature gun is required to calibrate the infrared sensor. Also, temperature probes placed in the vents as well as the vicinity of the foot well air intake. Verifcation of damper door calibration is also required. And the star machine to set the calibration. (Rich S, August 2011).