Relay Waveforms

Capture a waveform that shows both the control circuit change when it turns on the relay, and the power switching on to power something in the ABS system. (Use an oscilloscope with 2 channels to capture this pattern. You may have to carefully set the trigger to capture this.)

Record the waveform below with the time and volts per division, and explain what you're measuring.

With the ABS switched off, I measured the voltage on the system relay control circuit with one oscilloscope and recorded 0.5 volts at 86 and 0V at 30. In this case, the wiring diagram indicates that 86 and 85 being the control circuit, and 30 and 87 being the switch circuit. However on the diagram, 87 is the positive terminal of the switch, whilst 30 is the negative terminal of the switch, which is the reverse of what we've learnt in the course. I measured 86 because with no power running through, the switch should not be activated, therefore giving me 0V at pin 30. When I turned the power on, I measured the voltage again and recorded 12V at 86, and 12V at pin 30, which indicates the relay is good and the switching circuit works. I then used a second oscilloscope to catch the switching circuit waveform when the switch is closed and power runs through to pin 1 of the ECU.

Explain what is happening above.

For the relay to switch on, the control circuit needs a certain amount of voltage. When there is no power running through the control circuit, the switching circuit will be 0V. When I switched the ABS on after 200ms, the switch closed, and voltage could now go through the switch circuit. However, after 50ms, the voltage dropped to 10V for 50ms, and then raised back up to 13V. The reason for this drop was from the Pump turning on and testing itself, and then turning itself off.

ABS Pump Relay Waveforms:

Capture a waveform that shows both the control circuit change when it turns on the relay, and the power switching on to power the ABS pump.

Y Axis = Voltage On the Switching Circuit Of the Relay

X Axis = Time caught in 200ms intervals

Explain what is happening in the waveform.

The Pump Relay switches after 800ms. The Pump Motor then recieves a 12V supply at the switching circuit , activating the Pump. The Pump then turns off after 200ms, and slowly reduces it's Voltage

Observe what happens during the ABS self test when you first turn the key on. Watch the warning lights, and observe power at the wires with an oscilloscope. Then discuss what is happening in the ABS system during the Self Test.

When I turn the key on, the ABS warning lamp comes on. This is because the ABS is doing a self test. The system relay switch closes and voltage runs through to the Motor Pump Relay and Power at the pump jumps to 12V, and then after a few seconds switches off and voltage at the pump goes back to 0V. The lamp then goes off, indicating that everything is fine with the ABS.

Create A Fault in the system by slowing down a wheel speed sensor or safely shorting out an inductive wheel speed sensor while you are applying the brakes. (Don't short out a Hall Effect, or Magneto-Resistive sensor) As you are applying the brakes, notice if the ABS pump turns on, solenoids turn on, or if the hydraulic pressure changes in one of the brake circuits and shows up on the pressure gauge. Discuss what is happening below:

In order to slow down the rotor, I had to manually create friction against the rotor, but because the rotor was spinning too fast for my fingers I thought of just locking up the rotor before I turned the machine on. With my finger hard against the rotor preventing it to move, I turned the machine on, but noticed the pump wasn't doing a self test, so I had to slowly release the brakes until the pump could do a self test and then turn off before locking up the rotor. I quickly noted the hydraulic pressure in all 4 chambers of 1000Kpa. Then when I locked the rotor once more I noticed straight away the Pump turning on. I also noted the pressure in one of the chambers had dropped drastically but the other 3 chambers were still at 1000Kpa.

Catch an oscilloscope pattern when an ABS solenoid has actuated. What is the pin and name of the solenoid? How did you do it?

I caught this pattern by slamming on the brakes at 800ms. The voltage then went up to 5v and stayed. This means the solenoid was off until I slammed onto the brakes, then the solenoid turned on, and this is how I got my reading of 5V.

Draw the pattern