We all know that Range Rover is a very prestige stream, yet the brand is popular in numbers as well. Like a BMW SUV, the Range Rover 2001 uses the same engine management system as the series 5 E39 2001, and of course, it holds a very advanced CANBUS system which makes automatic communication and user’s comfort as efficient as possible.
The CANBUS system is like a universal communication language on vehicle’s electrical management, therefore it can be anywhere on a car from ECM, TCM to accessories etc… With this one, we take a look at the CANBUS for the ABS system.
Identifying wires are phenomenon, we would be expecting any “twisted pair” wires. This is because when 2 wires are twisted along each other, their magnetic field interferences cancel out each other, giving a clear signal.
The type of signal we expect from these types of wire is quite special as well. There will be a CAN HIGH and CAN LOW mirroring each other in signal. The signal is pretty much digital signal, one towards a CAN module which called a “node”; and one in vice versa to the first module, the two go back and forth.
CAN HIGH is the signal which starts with a relatively low voltage and switches to higher voltage when it needs to communicate. To the ECU, it’s like start normally zero and communicating by 1.
CAN LOW starts with a relatively high voltage but then grounded to low or zero voltage when it communicates. It’s like start 1 and then jump down to zero.
An oscilloscope with a dual trace setup can help us capture this signal on sight. Voltage and time division and be set to avoid “aliasing”. Aliasing is a term in CANBUS signal which describes a condition where there is a “ghost” signal frequently appearing out of phase with the “real” consistent signal. In prior to capture the signal by pressing HOLD, the aliasing can alter the real signal, giving us falsified CANBUS behavior and THIS jeopardizes CANBUS diagnostic.
Although Oscilloscope is easy and quick to set up to test the CANBUS but this is just a small test and you can only test one “twisted pair” at a time. Therefore we use scan tool as also a main device that gives us a general fault codes condition and actuation of the “WHOLE” system. A mislead is to try to find the CAN system after selecting brand and model. This is pointless because the CANBUS IS the language that communicates between systems from high speed CAN to low speed CAN and to the users that we can receive all the engine check lights and trouble codes when we turn on our scan tool.
Also, a misunderstanding is HIGH speed CAN and CAN HIGH, they are different by definition. High speed CAN is systems that runs on real time in prior to systems that affect mobility and safety of the vehicle(engine, transmission, ABS, Traction and stability control, auto door-lock, Inhibitor switch etc…) and Low speed CAN, you know, accessories in prior to user’s utilities(radio, CD players, windows, wipers, horns…)
There is a SLEEP MODE on the CAN systems, which allows the whole CANBUS to go to sleep, which means not communicating after a few seconds. This amount of time is for the nodes to collect and memorize all the necessary data before going to “sleep”, and it goes to sleep even when the ignition is OFF in prior to not losing all the data which is very useful for making the next start more efficient. Sleep mode replaces OFF mode for not draining battery overnight.
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