Scania fault code 121
Code 121 is used by 3 different Scania systems. Choose the control unit shown in your diagnostic tool:
VDT
Gearbox identification unit
Signal fault from identification unit.
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CUV Visibility system
Switch, S1.
All control unit inputs from S1 have been short circuited to ground for more than two minutes.
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ATA
Glow plug
The auxiliary heater does not start.
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