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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.

P1785 and P1740

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



- Unplug the connector.



- Turn the ignition switch to the ON position.



- Take voltage readings with a multimeter on the female connector contacts. Nominal voltages are as follows:

Battery positive across B+ and pin 4

battery positive across pins 5 and 4

1.0 V across pins 2 and 4



3.5 V across pins 3 and 4

Battery positive across B+ and pin 6


5.0 V across pins 7 and 4

10.0 V across pins 8 and 4, if "ON" is selected for the "CLUTCH ACTUATOR" command in the "ACTIVATE" menu.



All readings OK?

yes

Continue with point 2.


no

Repair or replace the lead in question and proceed to point 2.


2 Final check



- Clear the diagnostic trouble code.

- Perform a drive cycle by driving the car at varying engine rpm and loads for 5 minutes.

- Check whether the diagnostic trouble code has recurred.


Has the diagnostic trouble code recurred?

yes

Change the actuator.


no

The steps taken to rectify the fault were correct.