CAN, ABS, and Electronic Transmissions

CAN (Controlled Area Network)

How The System Works

CAN is a type of network that is used to control various systems of a car via control modules. 
Modules have 1 or 2 twisted data wires going to them referred to as twisted pairs. The modules are types of control systems that are used to control various areas of the car.
 for example, 1 module will control systems of the car doors, which would include: windows, locks, speakers and the door light. 

process of operation: (If I use the door module as an example)

1. Passenger pushes the window lowering button
2. Switch is wired into door control module and sends a signal across the CAN
3. The specific signal is especially designed to communicate with the window lowering motor. signal is converted into a 12V DC voltage and then activates the motor and the window is lowered.

Advantages and Benefits

This type of system has many advantages than the earlier systems, which used to have separate wiring looms for each component. Which made things much more complicated. CAN has eliminated a lot of the complexity because many modules can share information with less wiring.

This also reduces manufacturing costs because less components are needed, saves weight, and makes the system much more reliable because less connections and wires are required.

Testing Components of CAN Systems

Testing was done using a oscilloscope and back probing the connectors from the particular component. 

One of the components I tested was the ABS Unit of a Range Rover. This required me to locate the Twisted Pair that was running from the ABS unit then back probing each wire. which were Identified by the fact they were twisted together.

The colours of the wires were: Yellow with black stripe and the other was Yellow with brown stripe.

I then back probed the wires and recorded the waveform I observed.

1. 

   Twisted Pair of ABS unit. 1 of the wires

2. 

   Twisted Pair of ABS unit Both wires shown

The waveform was correct as it showed the signal the CAN system was sending and they were a mirror image of each other (as shown in Image 2). The lower wave form showed the CAN-L or low voltage signal and the one above it showed CAN-H or high voltage. Which is required for a good signal. This signal showed standby operating conditions of the ABS Pump.

ABS (Anti-lock Braking System)

How System Works

This system is used to reduce stopping distance under emergency braking conditions by preventing the wheels from locking up and sliding, by controlling how much braking is applied.

Under normal braking the pressure goes through the hydraulic valves like normal. But in emergency conditions the ABS steps in and begins to control the valves in 3 stages :

1. Hold Pressure: system closes the valves to prevent fluid pressure build up If this does not work and wheels are still locked up the Hydraulic Control Unit (HCU) then will;
2. Release Pressure: By opening up a valve that drains off pressure into a accumulator for later use. Wheels then will start to rotate and as it slows down more it then switches into; 
3. Restore Pressure: It does this by pumping brake fluid back into the fluid lines from the accumulator pump once car has finally come to a stop it returns to normal braking 

All this is done in milliseconds to make sure driver will stop in time while maintaining control of vehicle. 

This is also monitored by using speed sensors at each wheel. the sensor can determine how fast the wheels are turning compared to vehicle speed if they are not turning and vehicle is still moving it can determine that the ABS is needed.

Advantages and Benefits Of ABS

The main advantage is maintaining drive-ability of the vehicle under emergency conditions compared to a car without ABS Stopping distance is decreased, stability is maintained, handling is improved because vehicle is able to swerve around road hazards. In Ideal conditions.

Testing Of ABS  

ABS simulator off car

Testing can also be done using an oscilloscope and back probing connector pins determining the waveform of components  

Example of a ABS Relay waveform

Waveform shows when the pump is active, when ignition is turned on, and when pump is grounded.

Testing can also be done using a scan tool on ABS testing If system is functioning correctly the speed sensors should show that they are active and not producing strange voltages. 

If they are the scan tool will show this. An example of a cause in a problem would be because of a dirty sensor getting incorrect readings because of interference in the magnetic field. The car I tested ABS system was in good condition as picture shows:

Screen capture of the scan tools ABS testing
it shows car is not moving as it is supposed too.

Electronic Transmissions

How It Works

Electronic Transmissions are a form of Automatic transmission, but instead of using fluid pressure to select gears they use several solenoids and engine sensors to determine what gear is required for current conditions.

The sensors used include: the TPS sensor, MAF sensor, ECT sensor, and the vehicle speed sensors. These readings are interpreted by the transmission computer and the gears are selected depending on the vehicle speed and load.

The most important sensor in this system is the TPS (throttle position sensor) because throttle position is used to determine when the gears shift. If the TPS is wide open high fluid pressure is needed to allow for faster shifts if the TPS is closed the pressure will be low and more clutch slipping occurs creating much smoother and slower shifts. 

The ECU reads the voltage coming from this sensor to tell this. Low voltage high pressure high voltage low pressure.

The pressure is regulated by the shifting solenoids if the solenoid is off fluid flow is reduced and low pressure conditions are created. When the solenoid is powered and turned on, high pressure is created.

Advantages and Benefits

This system is much better because it allows for much more precise control of the gears compared to normal fluid control. Creating better engine performance, Fuel economy and reduces ware on the transmission its self.

Testing

Testing is done using the scan tool to determine if the solenoids are active and functioning correctly and at the right shift times. 

Scan tool showing shift times and active time of solenoids

Scan tool was put into transmission information and the car was driven on the Speedo-testing rollers and ran up to 80 Km/h and solenoid active time, duty cycle and engine speed was observed and recorded.