Here is the instruction show the simple steps on how to diagnose Scania truck alarm system high and low supply voltage ALM 256 257 error.
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Control unit, high supply voltage
Error identification
ALM control unit E7 has detected that its supply voltage has exceeded 36 V.
Cause
Fault in the alternator.
Incorrect connection of the battery.
Faulty ALM control unit.
Notes
–
Symptom
The control unit does not work.
Action
Check that the cable harness for the voltage supply is connected as per the electrical diagram.
Check the continuity in the cable harness between the battery and the ALM control unit with a multimeter.
Check the alternator.
If the fault is not in the voltage supply circuit or in the alternator, renew the ALM control unit.
Control unit, low supply voltage
Error identification
ALM control unit E7 has detected that its supply voltage has fallen below 16 V.
Cause
Fault in cable harness or harness-to-component connectors to ALM control unit E7.
Fault in the battery or alternator.
Faulty ALM control unit.
Notes
–
Symptom
The control unit does not work.
Action
Check that the cable harness for the voltage supply is connected as per the electrical diagram.
Check the continuity in the cable harness between the battery and the ALM control unit with a multimeter.
Check the alternator.
If the fault is not in the voltage supply circuit or in the alternator, renew the ALM control unit.
For more information about Scania truck,please refer to:Scania Trouble Repair.