On Car: CAN Multiplexing

CAN-Multiplexing

VEHICLE

Range Rover 2001-2003

CAN communication twisted lines 

1: Yellow with brown stripe

2: Yellow with black stripe

Time per division: 10us/div
Voltage per division: 1.00volt/div

The two twisted wire are the CAN
communications to the ABS Modulator 

Channel A (Low CAN) 

Colour of wire: Yellow/brown stripe

 Channel B (High CAN)

Colour of wire: Yellow/black stripe

Time per division: 1.00v/div

Voltage per division: 10ms/div

Both channel signals are opposite to each other with the same base voltage. the amplifier

compares these two different channel than create the digital signal. If the two becomes equal voltage than the signal must be 0v and gives the ECU digital the translation of 0v. When the H-CAN and L-CAN both different reference and tolerance, ECU digital translation would be as 1. The ECU would identify the codes and information that the CAN system is carried through the system. 

What is aliasing? Describe it

 It's a image imperfections arising from insufficiently detailed input to a "raster display" resulting eg in a  diagonal line appearing stepped.

How do you know these waveforms are not “aliasing”? 

 The signal looks digital signal, their different is they read to (0 or 1)

Multi-meter Test

Our Meter was capable of putting out digital reading for the CAN test. For the next test procedure the signal is very quit for the meter and so cannot give the information as it switch. And so we comes to oscilloscope which is useful tool that provide the information we

need especially the CAN system. 

1.3 waveform and the main voltage on the line

2.5volts

 When the voltage  pulled up and down to “talk” 

1.4volts

1.4 waveform above, what is the main voltage on the line?

            2.5volts

When the voltage is pulled up or down to “talk”

         3.6volts

Observe the signals in 1.3 and 1.4 above with a voltmeter. Compare it with DC volts or AC volts setting. Which setting would tell you if the signal is switching.

This is not an AC voltage therefore the signal giving out Direct Current voltage

Scan Tool Observations 

Vehicle: 2001 Range Rover  

Equipment used: AutoBoss scan tool

What different functions are available on the scan tool to examine the CAN system?

The scan tool show us the menu display of the body electronics CAN system

Fault codes, Actual values, Actual values and Actuation

List of different system controlled by CAN Low and High Speed

To ensure this output communication test work, we use the scan tool to activate different input in the vehicle system, we tested some of the system like wiper motor, headlight and many other units.

         Windscreen wash/wiper with headlight cleaning system, Interior lights and load cut OFF, Central-locking system, Electric windows, Burglar alarm system, and Mirror functions

Wiper motor at speed 2, Windscreen washer pump and Headlight cleaning system pump. 

Some of these system like central body control are convenience and they don't need fast response time including wiper,central locking, interior light ON/OFF are controlled by low speed CAN. High speed CAN comes with most important parts of the engine with more power and so they response quickly to the engine need, systems like Engine control, ABS, Fuel Emissions and etc. 

Wiring Diagram Exercise

Pin 23,24 are from high speed CAN system and pin 25 is the low speed system. The gateway changes the signal to different speed.

Sleep Mode

After awhile of all output components are turn off, the system will goes to sleep mode, this is where the battery save its energy, store memories and receive signal from the remote control or even the key  to wake the system. In the sleep mode, the system will drawn lower current than normal operation, this is up to 30mA. one example, you can wake up the central locking system to unlock the car doors.

Locate a system that goes to "sleep" after a short time.

06.0seconds

Awaking voltage  

0.2volt

sleep voltage:    0.416volt (DC)

On what wire do you see this voltage change? Yellow/brown

 Amp Drain:

Measure the amp drain at the battery when the system is asleep 27mA

Measure the amp drain at the battery when the system is awake: 30mA

How long did it take the system to go to sleep: 5minuts

What made the system “wake up”?  Key