Procedure in the Event of Quiescent Current Faults
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 modules 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 memory and correct stored faults!
If no bus rest is possible, it is necessary to determine which bus or control module 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 module, the corresponding control module can normally not waken the bus.
However, returning the bus to sleep can be disrupted by an internal control-module fault.
If no bus rest is possible in spite of disconnected fuses, the corresponding control module must be disconnected.
The overview of the buses and corresponding control modules 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 modules 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.