Fault code 4: Elimination:

• Visually inspect the sensor linkage and check the plastic holder of the sensor.
• Switch off ignition
• Pull plug off the angle sensor for HBA, rear 
• Switch ignition on
• Measure voltage between terminal 5 of the sensor plug and ground Voltmeter display approx. 5 V
• Measure voltage between terminal 5 and terminal 1 of the sensor plug
• Voltmeter display approx. 5 V
• In the PST2 menu item Actual values, select Sensor voltage, spring travel 2 (rear) 
• Connect a wiring harness jumper to terminals 4 and 5 of the sensor plug

  PST2 display approx. 5 V

If no fault is detected in the wires, replace the angle sensor for HBA.