ABS and Electronic Transmissions

The task to be done was to test the ABS(anti brake-lock system) using an ABS demonstrator which can be seen in the images below. This is done so that we know what wave forms to look for when we test ABS sensors in the future. The purpose of the ABS system is so that the car can stop in the shortest distance possible whilst the driver is maintaining control of the vehicle.

The first test we had to do was to test the signal coming out of each wheel speed sensor, this is a analogue signal which uses magnets on a toothed wheel which as the magnet passes by the pick-up or sensor voltage is induced. The ABS system needs wheel speed sensors so that the ABS module/ECU knows the speed of each wheel whilst under heavy braking. This is because if one of the wheels starts to lock up then you could lose the steerability of the car or even the stability or traction to the rear wheels of the car. If the ABS ECU sees that one of the wheels is spinning slower than the rest of the wheels then it determines that the wheel is locking up so the ECU will release brake pressure to that wheel to allow it to start spinning again. The ECU can determine wheel speed by the number of cross counts or peaks in the wave form the greater the amount of cross counts the greater the wheel speed.

^ABS Demonstrator wheel speed sensors^

^wheel speed sensor signal (LF)^

^Wheel speed sensor signal(RF)^

^Wheel speed sensor signal (LR)^

This signal has suck a large wave form because the sensor was much closer to the toothed wheel than the other sensors. This would cause a fault code in the system lighting up the ABS light, as this would read a signal that much stronger and it would look faster than the other wheels so the ABS ECU would think that wheel is spinning faster than the others which means the ABS would not work properly on that wheel under heavy braking and it would brake that wheel heavily, more than normal to try and slow it down as it thinks its spinning to fast, which could cause vehicle instability in the rear wheels.

^Wheel speed sensor signal(RR)^

There are three stages of operation when the ABS starts working, first of all a pump starts working to increase brake fluid pressure and continues working until the ABS system shuts off. Then there is an increase pressure in which the outlet valve is closed so that brake fluid cannot go back to the fluid reservoir or an accumulator tank, and the inlet valve is open so that brake fluid pressure can increase to the brake callipers.

Then there is holding pressure, this is when the inlet valve is closed, so that no more fluid pressure can enter and act on the brake callipers, and the outlet valve is closed so that no brake pressure can go back to the fluid reservoir or accumulator tank. This means that the brake fluid pressure is at a constant pressure acting on the brake callipers.

The last stage is release pressure, this is when the inlet valve is closed so that no brake fluid pressure can enter to the brake callipers to try and act on them. And the outlet valve is open so the fluid can be released back into the brake fluid reservoir or accumulator tank to be re-used again.

The above stages occur many times in split seconds whilst the ABS system is working, to ensure that the wheels do not lock up and allows the vehicle to stop without loosing control safetly.

A basic diagram of the ABS system can be seen below.


http://www.cvel.clemson.edu/auto/systems/images/Hydraulic_modulator.png

The next part to test for the ABS system was the relay powering up something in the ABS system and watch the reading using an oscilloscope, the wave for shows the coil and the switch, the top waveform shows the switch side of the relay when it is switched on and 12 volts is supplied to it. The waveform below shows the coil for the relay, the reason it has its peak and then drops off to zero is because when the coil is first provided power the ABS ECU has not yet provided ground or earth so voltage is at 12 volts on that wire, when the coil is grounded voltage goes to zero as now the coil is using the voltage to create the magnetic field and voltage has to be used up to get to earth, voltage remains at zero even when the coil is switched off as now there is no voltage being supplied to that coil.

The next waveform to measure using the oscilloscope was the ABS pump relay. The top waveform shows the ABS pump and the bottom waveform shows the relay. At point (A) the ignition is on, from point (A) to (B) there is a 12 volt supply voltage to the relay switch, and point (B) to (C) is when the coil/relay is grounded and powering the ABS pump. At point (C) to (D) there is 12 volts supplied to the relay but it is not grounded, at point (D) the ignition is off at point (D) to (E) the coil is grounded again, (E) to (F) is the 12 volts supply voltage. The top waveform shows the ABS pump operating, from point (G) to (H) the Relay is grounded so the ABS pump is operating, after point (H) the pump is off, which takes time for it to fully switch off even when there is no power being provided to it. Point (I) to (J) after point (J) to pump is off but once again it takes time to fully switch off.

What the above waveform is essentially showing is the ABS pump switching on for a set time when the ignition is on and when the key is switched off the ABS pump comes on again. The point in this is that if you you need to do an emergency stop and the engine stalls the ABS pump comes on so that high brake pressure is still maintained to the wheels. This is essentially a fail safe programme for your car so that high brake pressure can be maintained even when the engine is off.

The next part of the ABS testing system was to do an on car test, this involved finding and identifying the wheel speed sensor and then measuring the waveform output to the ABS ECU using an oscilloscope. The wheel speed sensor on the Daihatsu YRV that we used was an inductive or magnetic pick-up wheel speed sensor that produces an analogue signal, these sensors work by using a toothed wheel with magnets on it, as the magnet passes by sensor or pick-up  which is a coil that has current and voltage induced into it as the magnet on the toothed wheel passes by, It then relays the information to the ABS ECU and the ECU can determine how fast the wheel is spinning by the number of cross-counts. The signal that the wheel speed sensor produces can be seen below.

http://i81.photobucket.com/albums/j208/minhph1/WheelSpeedSensor.jpg

These are some of the procedures that you can go through to test the ABS system on all cars, to see whether the ABS system is working correctly.

ELECTRONIC TRANSMISSIONS

The electronic transmission normally uses two shift solenoids to act on or redirect transmission fluid in the valve body, so that they can hold or change gears by having the transmission fluid flowing to the bands to act on the clutch packs which inturn acts on the planetary gear set to give the different gear ratios.

Here is a shift solenoid chart below of the different solenoids that where on, for a 2008 mitsubishi lancer station wagon.

Gear:         shift solenoid 2 ,     L.R solenoid,     Over drive solenoid,      under drive solenoid

1st:                  on                        off                           on                          off

2nd:                 off                         on                         on                          off

3rd:                 on                         on                          off                          off

4th:                 off                          on                         off                          on

The next task was to measure when the torque converter clutch came on using a scan tool, the result that I got was when the car was at a constant cruise in third gear or higher the torque converter clutch came on. This is to lock the turbine and impeller in the torque converter together so that a 1:1 ratio is created and the maximum power and fuel efficiency can be created. The torque converter clutch(TCC) solenoid would switch off when the car is decelerating or the vehicles speed is constantly changing as this gives the driver smoother gear shifts. When the brake pedal is pressed the TCC solenoid switches off as it presumes that the driver wants to slow down so their is no need to deliver drive to the wheels any more.

These are the very basics on how a electronic transmission works and how the different solenoids switch on and off at different times to give the transmission its different gear ratios. 

Multiplexing Worksheet

                                                    C.A.N Waveform on Oscilloscope

The task to be done was to test and check the C.A.N (controller area network) system on a 2001 Range Rover. This was done by using an oscilloscope to measure the voltage waveforms and a scan tool to check for codes in the controller units or nodes. The purpose of the C.A.N system is reduce the amount of wires going through the car, instead of each actuator having wires going to it now theres only two wires going between nodes (Control units) and then wires going to each actuator which means that wire length is largely reduced since the node is placed in a central location.

The first task to do was to find the twisted wire pair which is the indication to where the C.A.N communication lines are located. The twisted pair is located next to the front left strut tower in front of the A.B.S(anti-lock brake system) module. Using an oscilloscope the voltage wave form was captured to see what code is being sent, as the C.A.N system uses binary code to talk to other nodes, this means that the voltage increases like a digital signal so each node gets codes in the form of 0's and 1's for example to low voltage which is 1.3 volts would a 0 and the high or on voltage of 2.4volts would be a 1. So the code could look something like this 1100010101000111, and the node would decipher this code into something that it can use for example this theoretical code could tell the A.B.S module to activate as heavy braking is being applied.

When setting the oscilloscope to read to the code it had to be made sure that time wasn't to long that aliasing is created, this is when a signal is jumbled as it is happening to quickly to make any sense. So the oscilloscope time per division was 10us (micro seconds) this means that this is a high speed C.A.N system so this is for systems that need to act quickly and are priority like A.B.S systems or traction control and other stability control programmes. Then there is a low speed C.A.N system that has a much slower signal rate that is used for low priority items such as windscreen wipers or interior lights, items that dont need to be fast acting.
The first C.A.N wire in the twisted pair we tested was a yellow wire with a brown stripe, this wire increased its voltage from 1.3 volts to 2.4 volts, this means that the voltage increases to talk this is also known as C.A.N high. Then there is C.A.N low which was a yellow wire with a black stripe with C.A.N low the voltage decreases from 3.7 volts to 2.6 volts to talk or send code to other nodes.

http://www.picoauto.com/automotivetopics/images/canbus_waveform_2.jpg


The reason that the C.A.N wires are twisted together is so that voltage is not induced from other wires that could interfere with the codes being sent down the communication wires which could mean that incorrect information could be sent or information that does not make sense meaning that if you want the windows to open nothing may happen.

C.A.N systems can be scanned for error codes using scan tools just like the ECU, with the Range Rover there are three main areas that the C.A.N system can be scanned there is the drive, the chassis, and the body. The scan tool can be used to read codes and clear codes but it can also be used to remotely control different functions in the C.A.N system for example you could control the electric mirrors and adjust them using the scan tool or you could open windows or switch on the windscreen wipers all using the scan tool. The reason this is done is so that all the actuators in the C.A.N system can be checked to make sure everything is in good working order. The scan tool we used was an Auto Boss, as it had so many more functions than the other scan tools. The next part of the check for the C.A.N system was to list all the different systems that are controlled by C.A.N this was done under the chassis section of the scan tool so this included,

ABS/ASC/DSC (Dynamic stability control) C.A.N High Speed
LEW/LWS (steering angle sensor) C.A.N High Speed
EDC(electronic damper control) C.A.N High Speed
RDC (tyre pressure check/RDW) C.A.N Low Speed
MFL (Multi Function steering wheel) C.A.N  Low Speed


The next part of the test was to put the system into sleep mode however we had trouble putting the system into sleep mode as we probably hadn't shut everything off properly so the C.A.N system remained active however the purpose of sleep mode is to reduce parasitic draw, parasitic draw is when battery voltage is being drained to power different things when the engine or ignition is off. Not all of the modules or nodes are connected to the ignition so there needs to be a signal sent to the nodes to tell them to sleep from other nodes. Any of the nodes can send a signal to tell other nodes to wake up or come into active mode. The CAN low system base voltage goes to a steady level like 5 volts and remains at a constant voltage when the node goes into sleep mode, then when its active the voltage will drop its base voltage to 3.5 volts. CAN high reduces its base voltage when it goes into sleep mode to around 0.5 volts, and when its active the voltage will increase to around 2 volts. These figures do vary for different manufacturers, and for the honda multiplexing board it took around 10 seconds for the board to go into sleep mode however it could take up to two minutes for the C.A.N system to fully go into sleep mode. 

HONDA MULTIPLEXING BOARD WORKSHEET

The multiplexing board we used was C.A.N parts from a Honda Accord that was used from 1996-2002, the board uses two nodes (control units) from the Honda cabin/interior C.A.N system and is used to help us learn C.A.N diagnostics. 

There are two modes that the multiplexing unit can be put in to aid with C.A.N diagnostics, mode 1 is used for diagnostics for communication lines between nodes. Mode 2 is used for inputs, if everything passes these tests this would mean that the fault is an output.

The first part of the task was to identify the plugs/pins and wire colours for the communication lines between the two nodes on the board. 

Multiplex Control unit driver door - brown wire, pin: A15-A2 

Driver node to passenger node - pink wire, pin: B1-B9

The next part was to Identify the plugs/pins and wire colours for the earths and power supply lines for the two nodes.

Ground wires and terminals: Drivers door Multiplex control unit - black wire, Pin: A12-G401, A14-G551 left door and right door nodes, G581

Passenger Multiplex control unit - Black wire, Pin: B22-G501, A8-G401.

12 Volt supplies from battery/alternator - pink wire, Pin: A1 ,A12 ,A24

Once all the pins had been identified we got the tutor to place a fault in the board and see how it affected the operation of the system. The fault we got was with the rear passenger door lock actuator, it would lock (if it was connected to a door) but it would not unlock, meaning that the rear passenger door would never unlock.

Now using a wiring diagram we had to determine what the problem might be and what is causing it to stay locked. After I looked over the wiring diagram I thought that the fault might be no power/voltage going to the unlocking relay of the door lock actuator.  Then we had to put the system into diagnostic mode so we put it into mode 1 and listened to see whether there where any fault codes, fault codes in the C.A.N system are much like check engine flash codes except instead of flashing a code the system will beep the code to you. However there where no codes.

The next test was to check whether there was continuity for the communication lines between the nodes. If there was no continuity between the communication wires then the nodes can not communicate with each other and this could mean that certain things cant work as there is no signal telling the actuator to work or operate. There was continuity and voltage available between the communication lines and there was continuity to earth or ground, this leaves a problem with the input side of the unlocking door actuator. This can be tested by putting the multiplex system into diagnostic mode 2, this is done by switching on mode 1, when mode 1 beeps to indicate that it is in diagnostic mode, switch it off for around 7 seconds and switch it back on again, it will indicate that it is in diagnostic mode 2 by doing one long beep and two short beeps. If all the inputs are working then the system will beep when you switch something on, the system did not beep when it came time to unlock the door lock actuator indicating that there was in-fact an input problem to the unlocking side of the actuator.

This means that my diagnosis of there being no power going to the unlocking relay was correct, as there was no voltage going to the unlocking relay. The tests that could have been carried using the wiring diagram was to check whether there was available voltage for the drivers door key cylinder switch, which is a blue wire coming from the pin: A16 to Pin 1(drivers door key cylinder switch) this means that there was no signal coming from pin A16 to the unlocking relay.

These are some of the tests that can be done to test and diagnose the C.A.N system on most cars from the mid to late 90's and onwards.