Scania fault code 4221
Code 4221 is used by 3 different Scania systems. Choose the control unit shown in your diagnostic tool:
EMS Engine Management System
Exhaust gas pressure sensor T125
The engine control unit indicates too low a voltage in the circuit for the charge air pressure sensor.
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EMU
Heater H39, high currents
The heater is reporting a current of over 26 A.
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DDU
Internal amplifier, overheating
An internal sensor has detected too high a temperature in the internal amplifier.
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