Procedure in event of quiescent current faults

This document describes the troubleshooting procedure in the event of quiescent current faults.

In the event of quiescent current faults, the following differences must be taken into consideration:

• Quiescent current too high:
  
  • through vehicle not going to sleep
    
  • through waking of bus
    
  • through fault control units or other components
    

Troubleshooting sequence in event of quiescent current faults

First check whether the correct quiescent current value sets in through forced sleeping with a Power Down command.

Reason

The time period for a normal sleeping procedure is over 1 hour. To reduce the time for troubleshooting, there is the possibility of letting the vehicle go to sleep immediately through a diagnosis command (Power Down).

Power Down command

To place the vehicle in Power Down mode, it is essential for the following preconditions to be satisfied:

• DIS Tester connected
  
• Terminal R off (but vehicle must not have gone to sleep yet)
  
• Remove key
  
• No charger connected
  

Send the Power Down command with a suitable test module

• Disconnect OBD plug
  

The Power Down mode is terminated when the bus is woken.

Troubleshooting procedure:

1. Forced sleeping

Procedure:

• Connect the DIS Tester to the vehicle
  
• To measure the quiescent current, connect the current probe directly to the battery
  
• Terminal R off (but vehicle must not have gone to sleep yet)
  
• Remove key
  
• Switch on the vehicle's reading light (serves to check the Power Down command)
  
• No charger connected
  
• Leave the driver's door or window open (to disconnect the radio head)
  

Send the Power Down command with a suitable test module

• Disconnect the OBD plug (on account of radio head's current consumption)
  

The vehicle must go to sleep approx. 20 seconds after the Power Down command is sent.

Identifying features:

• First the reading light goes out
  
• Start-button illumination goes out
  
• LEDs of seat adjustment switches go out
  

If the identifying features indicate that the vehicle is sleeping, a quiescent current measurement can be carried out after approx. 30 seconds.

The total quiescent current must be < 30 mA

Important: Do not perform any actuations during the measurement. The Power Down mode is terminated when the bus is woken.

2. Natural sleeping

Start-button illumination goes out after approx. 2 minutes (after removal of ignition key).

In the case of the natural sleeping process, a quiescent current of < 30 mA must be reached after approx. 70 minutes.

3. Procedure if bus does not go to sleep

Identifying feature: (after removing ignition key)

• Start-button illumination does not go out after approx. 2 minutes
  
• or goes out briefly and then comes on again
  

Precondition: Read out fault code memory and correct stored faults!

If no bus rest is possible, it is necessary to determine which bus or control unit is preventing the bus from going to sleep.

Procedure:

Perform forced sleeping with Power Down command.

Does the bus go to sleep with the Power Down command?

Note!

If a fuse is disconnected from a control unit, the corresponding control unit can normally not waken the bus.

However, returning the bus to sleep can be disrupted by an internal control unit fault.

If no bus rest is possible in spite of disconnected fuses, the corresponding control unit must be disconnected.

The overview of the buses and corresponding control units can be reached via the bus functions.

4. Quiescent current measurement

A quiescent current measurement is to be run in the case of bus rest.

Begin by measuring the quiescent current with the current probe directly at the battery.

If the quiescent current is less than 4 A, the measurement adapter can be installed for precise measurement.

In order to pinpoint the cause of the quiescent current, measure at the high-current outputs on the power module. This is a quick way to pinpoint the general location of the cause of the quiescent current.

• Distributor, engine compartment
  
• Distributor, luggage compartment
  
  

At the corresponding distributor, disconnecting fuses enables detection of the cause.

Control units that are not protected via the distributor in the engine compartment or luggage compartment must be determined individually by disconnecting the corresponding fuses or the units themselves.