Checking the Grounding
1 Connect a BOB and check whether voltage is present on pin 20 and battery positive.
The reading should be 12v.
Note: Disconnet the battery cable before removing the grounding point. If this is not done the control modules in the car could be rendered unserviceable.
2 If the voltage reading is not OK, check the wiring for continuity/shorting.
Also inspect grounding point G3S visually, unscrew and clean the contact surfaces. Reconnect the grounding point and battery cable, and repeat point 1.