CAN Multiplexing

We used 2001 Range Rover to access CAN system. Wires for can High and Low were found at ABS control unit.













Colour of wires:
Yellow with black stripe and yellow with brown stripe.
50 micro sec time division
2 volts per divition

Here is an oscilloscope pattern from can of Range Rover. It has both can Low and Can High.


Aliasing means - a jagged, stair step effect on curved or diagonal lines that are reproduced in low resolution, on a computer printout or display.

Main voltage on can high is around 2.5 volts and when its pulled down it goes up to 4,2-4.5 volts
Main voltage on can low also around 2.5 volts but it pulls it down to around 1.2 volts.

We checked DC and AC voltage at the wires, dont know if we done it exactly right but DC reads 0.27 volts and AC reads 0.57 volts.

Then we tested Range Rover with Auto Boss scan tool and found that every single system or unit which within the can system we can trigger it or operate from a scan tool. Can system can be also checked for faults in the actual system.


Can system designed to cut cost on wires and provide communication between different modules so they all can send and receive information and exchange it between each other, also this system requires less wires and can be diagnosed with proper scan equipment and modules can be exchange onto new ones if they faulty.

Controlled Area Network

Here is an oscilloscope pattern of CAN data stream. Blue with white stripe is a can high wire and yellow wire is for can low, black is a ground wire. This system can be only tested with dual trace oscilloscope as high and low has to be connected together to see full pattern.


Right indicator pattern.













Left side indicator























Rear wiper.



















Stop Lights.





















Fuel Pump.








Input and output pins or right indicator and rear wiper.

Right indicator input pin 5 and output through U7 transistor from IC9 chip. (GP4 pin 5 of IC)

Rear wiper input pin 7 and output trough RL4b relay and transistor U14. (GP6 output from 14 pin IC chip MCP2505)


Identifying voltage regulators.

Pin 1 and 2 12 volts power supply, regulator number U2 7805, output +5 volts to pin 14 of IC MCP 2505.

Following reverse light circuit.

Input switch pin 4 to pin 3 in 18F258 from that it goes as a digital signal in can High and Low to IC 4 then to IC 5 and IC 5 sends signal to MCP 2505 which sends ground signal in pin 2 to IC 7 which turns on the transistor U5 which grounds reverse light and turns them on.

Electronic Transmissions and Scan Tools

Here is some abbreviations used for workshop manuals.

PCM = powertrain control module
TCC = torque converter clutch
TPS = throttle position sensor
ECT = engine coolant temperature sensor
VSS = vehicle speed sensor
(TR)PSA = transmission range fluid pressure switch assembly
TTS = transmission temperature sensor

This are used in many manuals and around technicians.

Here is a photo of automatic transmission life data. We can see various sensors and shift solenoid A, B and over run solenoid.







Wiring diagram for a PCM.















Using Holden shift chart identify which solenoids are on when:

1. When car shifts onto drive solenoid 1-2 and 2-3 are on.
2. When it shifts onto second gear automatically, solenoid 2-3 is on.
3. When shifts automatically onto third gear, none solenoids are on.
4. When shifts onto fourth gear, solenoid 1-2 is on.

So in the case of none solenoids are on the car remain in third gear constantly and can be only driven to the appropriate service center to get repaired.


Then we pick up two trouble codes out of repair manual.

First is Engine coolant temperature (ECT) signal too high. In this case car can drive on all gears except over drive i would say as my one does that until its cold for a few minutes. As transmission control module will always think that engine cold and not at the appropriate working temperature. ECT sensor can be checked on resistance matching certain engine temperature and volt dropped at the signal and ground wire and also supply voltage must be checked.

Next Vehicle Speed Sensor signal low, in this case i would say vehicle will go into fail safe mode and transmission wouldn't work properly only on that gear when both shift solenoids are off. As vehicle can see what speed is it driving it doesnt now which gear to change when. VSS can be checked with oscilloscope or a scan tool using a life data feature also wires must be checked for broken circuit.

Then we used a Hannatech scan tool on Nissan Cefire 1997 with automatic transmission.

Here is a Nissan Cefiro shift shart.

So when both solenoids are off car remain in third gear and if they are not working it still can move but only to a service station to get repaired.

On Vehicle Testing ABS system

We used a little Mazda Demio for out test of ABS system on car. Here fer fotos of ABS system components on Mazda Demio.












Wheel speed sensors. We identified that sensors are inductive pick up and captured pattern on the right front wheel. Inductive pick up wheel speed sensor will generate its own AC voltage and will increase its amplitude and frequency with faster speeds and its an analog signal not digital.
Measuring the air gap for wheel speed sensors. Front right 0.711 mm and front left 0.55 mm. The air gap is very important for inductive wheel speed sensors and can affect the output signal by generating not enough voltage as ECU looks at particular voltage and can interrupt proper working of ABS system.







Analog signal pattern. We also recorded a Frequency of this sensor with multimeter and it was 72.39 Hz. This frequency shown how fast signal changes from positive voltage to negative voltage. Showing that wheel speed sensor working but doesn't show how good is it working.















Using a scan tool we can see life data of ABS sensors and solenoids. As we rotate front right and rear right wheel we can see change in speeds of both wheels when car on a hoist. Also we can see if ABS motor on or off and various ABS valves. Also we used Honda Accord Euro R 2000, the one Adams drives, as we can go to actuators test and test ABS solenoids. During the test brake pedal was vibrating as when ABS working. So with test we can find which solenoids are seized or not working properly.

And this test we done on Nissan Cefiro 1997, we actuate solenoids driving around 30 km/h on a grass and braking hard as an emergency stop. This proofs that ABS system works even at low vehicle speeds. On a picture we can see ABS motor is on and Solenoids (in) are on as well. So ABS is a safety system for late model vehicles providing driver with steereability and stability in emergency braking situations.

ABS relay

Capturing oscilloscope pattern of ABS relay with two channel oscilloscope.

We used two pin probed to connect to power side of the relays.
ABS main relay number K38 and ABS motor relay number K100


Here is an oscilloscope pattern of ABS main relay and ABS motor relay.

On this graph we can see ABS ECU relay self check when its firs turned on (top graph on the photo).
Also we can see that ECU check ABS pump, it triggers it as power goes to 12 volts and them we can see osculation as the pump stops (bottom graph)


This first self checks required as the car which has got ABS system in it also have an ABS warning light, this is for the driver to inform of the conditions of ABS system. If light goes off in around 5 seconds after the car first time started, it means the system normal and in working conditions. When light stays on constantly this will mean system faulty and need attention and will not work until fixed.

We used plastic pipe to slow down Left rear wheel speed sensor and also captured and oscilloscope pattern of ABS motor. On the picture we can see that when brakes applied and ECU detects one of the wheels rotates slower then the others it turns on the ABS pump to ether decrease or increase braking force on that wheel.