CAN - Multiplexing Worksheet

1.1  locate the Range Rover or other suitable vehicle with easily accessible CAN system twisted wires. Which vehicle do you have?
   Range Rover, 2005

1.2  locate a twisted wire pair. Describe where the wires are located: Next to the ABS module in the engine compartment.

Record the waveforms:

This waveform is the one of the L CAN fast CAN ABS which was a yellow wire with a brown stripe. Time Div. 5 micro seconds Voltage Div. 1V                                                                                             

This waveform is the one of the H CAN also on the fast CAN because it is the H CAN on the ABS and is a yellow wire with a black stripe

What is Aliasing?

"Jagged,stairset effect on curved or diagonal lines that are reproduced in low resolution as on a computer printout or display"-from Dictionary.com

The waveforms i captured from the ABS CAN in the above images are not Aliasing because the both waveforms are clear and correct.

the main voltage for the L CAN is 2.5v

     "          "             "           "          2.5v

The voltage that is pulled down on the L CAN is 1.4V

The voltage that is pulled up on the H CAN is 3.5V

1.9 Observe the signals from the H and L wires with a voltmeter. Compare it with AC volts and DC volts setting. Which setting would tell you if the signal is switching?.

          H CAN       L CAN

DC      2.36V        2.62V

AC     0.1mV        0.1mV

The DC setting would tell you if the signal is switching because it only measures positive voltage signals whereas AC reads both Negative and Postive voltages and in this case we are only dealing with positive voltages therefor the DC setting is adequate.

Scan tool observation

The vehicle i used to plug the scan tool into was a 2005 Range Rover and the scan tool i was using was an Autoboss.

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

-control unit version

-fault codes

-actual values (All select)

-acual values (manual select)

-actuators

2.3 list the different systems that are controlled by CAN? (note which are high speed and which are low speed)

High speed:

-Air bags

-instrument cluster

-ABS

Low speed:

-lights

-wiper

-washer fluid

-central locking

-window acuators

-mirror

-air cond

The system which goes to "sleep" is the CAN system after a short time, the vltage you see when its awake is 2.5-2.6v DC and when its asleep you see 0.2mV DC and the wire in which this voltage chage occurs is the L CAN wire (yellow wit brown stripe).

The amp drain when the CAN system is asleep is about 40mA and the System takes around 2 seconds to go to sleep and by simply unlocking a door will wake up the system.