The first step would be a visual inspection, we would need to check if someone could have damaged the ABS module or the plug has come unattached. If someone has probed into the wires, then this will cause added resistance. We can use a oscilloscope to see what pattern we get from the wheel speed sensors because if the gap between the sensor and the rotor is too big, then it will send an incorrect reading to the ECU. If a spike has gone through one of the wires due to careless wielding, then we can use an oscilloscope to study the wave patterns the CAN-BUS is giving us to see weather it has caused any damage.
Wiring Diagram Practice
Wheel Speed Sensors Wire Colors:
Front Right - Brown, White
Front Left - Green, Red
Rear Left - Blue, Pink
Rear Right - Brown, Yellow
The ABS wheel sensor have braided wire so that no other kind of wave signal can interfere with the signal.
Fuses:
ABS Fuse (50A)
ECU Fuse (13A)
Stop Light Fuse (10A)
Dome Fuse (20A)
Gauge Fuse (10A)
Main Fuse (3W)
Earths For ABS:
The ABS control unit earth pins are 10B and 7B (White/Black) and the ABS motor earth pin is 1A (White/Black)
Wheel cylinder wire colors and pin numbers
Front Right Wheel
Pin Number - 6B, 5B
Wire Color - Red/White , Red/Green
Front Left Wheel
Pin Number - 1A, 2A
Wire Color - Blue/Red , Blue/White
Rear Left Wheel
Pin Number - 12B, 11B
Wire Color - Brown/White , Brown/Red
Rear Right Wheel
Pin Number - 14A, 15A
Wire Color - Green/Black , Green/Yellow
In Case 4 the ABS motor will start working when there is increase in brake pressure.
Digital Signal
This Waveform switches 5volts every 2 seconds.
Analogue Signal
This Waveform has a frequency of 0.5 Hz and a maximum of +3 volts.
ABS Demonstrators
The ABS demonstrator i used had and inductive wheel speed sensor. How it works is inside the sensor there is a magnet, so as the rotor teeth moves closer to the sensor, it induces a positive voltage (magnetic field) as the tooth moves away, the magnetic field collapses creating a negative voltage. This creates a AC waveform.
Wheel Speed Sensors
The waveform max voltage is different from one another. The gap between the rotor teeth and the inductive sensor are different. If the gap between the teeth and the sensor was small, it would result in a higher output voltage, if the gap was large, it would result in a lower output voltage.
The mulimeter can only give us a reading of the inductive sensor but the oscilloscope can show us a wave pattern of the sensors output signal which can show us if one of the teeth on the rotor is broken or if the gap between the rotor and sensor is too large or too small.
ABS Relays
Protection Relay - Powers up the ABS ECU
Pump Motor Relay - Powers up ABS Pump
System Relay - Send power to the ABS HCU Solenoids
Relay Wire Identification
ECU pin that brings in power to the ABS ECU - Pin 1
ECU pin for the wires that control the relay for the
ABS ECU - K39, pin 86 and 31
Pin 13 - Brings power to the ABS Pump
Pin 2 and 11 - Controls the relay for the ABS Pump
Relay Waveform
At point A, ignition is switched on and the relay switches on. At point B the ABS system does a self check which will test the solenoid valves by the relay switching on and off. At point C, the relay gets switched on then off to complete the test. So now we have voltage at pin 85 (point D). At point E the ABS ECU will go into a standby mode so the relay gets grounded. At point F we see the solenoid operation for the self check, and at point G back EMF is created when the ignition is switched off.
ABS Pump Relay Waveform
At point A ignition switched on and we have supply voltage. At point B ABS ECU grounds the relay so the relay switches on and the pump motor turns on (point C). After the self check the pump relay switches off so we have supply voltage at point D and or at point F. Back EMF is created when the pump relay switches off (point E). At point G/H the brake pressure gets low and the ABS ECU switches the pump relay on. When the brake pressure returns to normal, the ABS ECU switches the relay off (point I) and back EMF i created when the relay switches off (point J)
ABS Self Test
When you turn the key on, the ABS light turns on then goes off. The ABS ECU tests the conditions of the solenoids valves by grounding the HCV relay and the pump relay and then switches off. This is to see if everything is working properly in the ABS system.
This is a Analogue pattern.
Frequency = 1/T = 1/2ms = 1/ 0.0025 = 500Hz
The oscilloscope pattern is much easier to understand then frequency readings on a multimeter.
Using a Scan Tool
Live data Screen: Sensors
ASC - If the ASC is activated
TPS - where the throttle on the engine is.
Brake Pedal - How much brake is applied.
Hand/Parking Brake - If hand/parking brake is applied.
Pump Motor - If the pump motor switches on or not.
ABS Valve Relay - If the relay is switching.
Actuator Test Screen
Return Pump - You can hear the pump switching on/off.
Inlet Valves (FL) (FR) (LR) (RR) - Solenoid activated by the ECU.
Outlet Valves (FL) (FR) (LR) (RR) - Solenoid activated by the ECU.
Electronic Transmission and Scan Tools
PCM - Powertrain Control Module.
TCC - Torque Converter Clutch.
TPS - Throttle Position Sensor.
ECT - Engine Coolant Temperature.
VSS - Vehicle Speed Sensor.
PSA - Pressure Switch Assembly.
TTS - Transition Temperature Sensor.
Shift Solenoids
1-2 and 2-3 solenoids are on when the vehicle is shifted into drive and starts out in first gear.
2-3 solenoids are on when the vehicle automatically shifts into second gear.
No solenoids are on when the vehicle automatically shifts into third gear.
1-2 solenoids are on when the vehicle automatically shifts into fourth gear.
Shift solenoids Malfunction
If none of the solenoids came on you would only get third gear. The vehicle will be drivable but will struggle to take off. You would be limited to a speed of about 80Km/H. It would struggle to climb a hill if the vehicle was at 0KM/H prior.
