Parasitic Battery Drain Testing
Figure 1.0 - Vehicle Electrical System Layout
These can be systems such as the following:-WI-FI - Internet and Hot-Spotting Services.In Car Entertainment Systems - Radio, SAT NAV, Multimedia, RSE, USB, DVD, TV.GPS - Tracker and Location Systems, SAT NAV.GSM - In Car Phone Systems.Telematics Systems - Combined GPS, GSM, WIFI, USB Systems
Powertrain Systems - Emission Control, Power Control, Safety Control.
Comfort Systems - Heated Seats, Lumbar Massage, Pneumatic Systems.Safety Systems - Airbags, Seat Belt Pre-tensioners, Impact Detection
This has included systems such as the following:-
CAN Bus - Used for most ECU to ECU Communications throughout the Vehicle
- High Speed CAN- Medium Speed CAN- Low Speed CAN
Example CAN Systems
- Comfort System CAN- Drive System CAN- Entertainment CAN- Safety CAN
Flex Ray - Extremely Fast Protocol used more for Chassis and Suspension SystemsK-Line - Diagnostic Communication often gateway to the ECU Fault Code EEPROMLIN Bus - Used for most Comfort Control Systems such as Seats.MOST Bus - Used for In-Car Entertainment and Multimedia systems.
On most modern vehicles all these Communication networks will all be able to interact with each other through the use of a 'Gateway' device which allows better diagnostic capabilities but also better control of the vehicle using different systems to interact with each other.
Example of 2 Vehicle Systems networked together to form an Enhanced Control System
Figure 2.0 - ESP System Overview.
Example Layout of Multiplexed Systems
Figure 3.0 - Typical Multiplexed Network Layout
What is a Parasitic Battery Drain?
- Relay Contacts can fail causing a permanent power drain.
- Alternator Shorted Diodes can cause a permanent power drain.
- ECU's not powering down properly (sleeping) can cause a permanent power drain.
- Electrical components keeping ECU's awake.
Common methods of searching for Parasitic Drains
In Line Fuse Testing
Another method is to use an in-line fuse breakout device and a current clamp and test each individual circuit for current draw until the circuit showing the excessive drain can be found.
Modern Electrical Systems
In order to complete Parasitic Drain Testing with the PicoScope Automotive Oscilloscope the following equipment is required:-
- PicoScope Automotive Oscilloscope
- CAN Test Box (Not Essential)
- 60/20 Amp Current Clamp
- BNC to 4mm Test Lead
- Unshrouded Adaptor (Used with CAN Test Box)
- Flexible Back Pinning Probe (Red)
- Flexible Back Pinning Probe (Black)
Setting up the PicoScope Hardware
We did this on a 2001 Vauxhall Vectra 2.2 CDX Z22SE
Waveform 1 - Vehicle Electrical Shutdown Waveform
Waveform 2 - Alternative Vehicle Shutdown Waveform
It can be seen that on the Vauxhall Vectra waveform the system shut-down period is extremely quick and is at zero within 1.5 seconds.