P1785 and P1740
Symptom: The "CHECK ACS" warning lamp is alight. System functions are disabled and the clutch cannot be operated. The car is undrivable.
P1740: Clutch actuator unit, internal fault P1785: Control module - clutch actuator unit, communication fault
Fault symptom
The "CHECK ACS" warning lamp is alight. System functions are disabled and the clutch cannot be operated. The car is undrivable.
Condition
P1740: The control module records an internal fault in the clutch actuator unit.
P1785: The control module and clutch actuator unit communicate with each other via a serial bus. Fault in the bus connections, shorting to ground or B+, or open circuit. Communications fault, incorrectly sent or received data. No power supply (+30 circuit, ground) present at the clutch actuator unit.
Diagnostic procedure
1 Check the clutch actuator unit's electrical connections
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Turn the ignition switch to the ON position.
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Take voltage readings with a multimeter on the female connector contacts. Nominal voltages are as follows:
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Battery positive across B+ and pin 4
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battery positive across pins 5 and 4
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1.0 V across pins 2 and 4
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3.5 V across pins 3 and 4
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Battery positive across B+ and pin 6
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5.0 V across pins 7 and 4
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10.0 V across pins 8 and 4, if "ON" is selected for the "CLUTCH ACTUATOR" command in the "ACTIVATE" menu.
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All readings OK?
Continue with point 2.
Repair or replace the lead in question and proceed to point 2.
2 Final check
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Clear the diagnostic trouble code.
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Perform a drive cycle by driving the car at varying engine rpm and loads for 5 minutes.
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Check whether the diagnostic trouble code has recurred.
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Has the diagnostic trouble code recurred?
Change the actuator.
The steps taken to rectify the fault were correct.
