-Spiked by careless welding, i.e. MIG welding without disconnecting the battery.
-Enclosure seal damaged and with obvious sign of water ingress.
-Obvious signs of mechanical damage to the enclosure.
ECU modules almost never give any trouble, its most of the time sensors, wiring and connectors.
To check for faults, first of all check wiring, connections and sensors and use proper testing equipment such as scan tool.
ABS wiring and operation.
1 = Disk Rotor.
2 = Wheel speed sensor
3 = Interrupter ring
4 = ABS pump assembly
5 = Brake master cylinder
6 = Brake caliper
7 = Brake booster
Wiring diagram practice.
Identifying wheel speed sensors and their color code wires.
Front right: green and red.
Front left: white and black.
Rear left: pink and blue.
Rear right: yellow and brown.
ABS wheel sensors has got braded wire to stop interference from other wires and devices.
There are some fusible links in ABS wiring:
ABS main fuse 50 amps
Gauge fuse 10 amps
Stop light fuse 15 amps
ECU fuse 15 amps
Dome fuse 20 amps
Identifying earth wires for ABS control unit:
ABS control unit
Pin #10 and #7, color white-black
ABS motor/pump
Pin #1, color white-black
Identifying which solenoid controls which cylinder:
Front right wheel - pin 2 and 6, color red-white and red-green
Front left wheel - pin 3 and 7, color blue-red and blue-white
Rear left wheel - pin 1 and 5, color brown-white and brown-red
Rear right wheel - pin 4 and 8, color green-black and green-yellow
1. Under normal braking Inlet valve open and Outlet valve closed.
2. When ABS is operating to reduce brake pressure Inlet valve closed and Outlet valve open.
3. When ABS is operating to hold brake pressure Inlet valve closed and Outlet valve closed.
4. When ABS is operating to increase wheel brake pressure Inlet valve closed and Outlet valve open.
So ABS motor will be working when brake pressure needs to increased or decreased.
This sensor works by generating AC voltage when interruption ring (rotor) rotates and cuts across the windings of the sensor.
This sensors can give wrong reading easily, as they are constant magnets and they can attract small metal chips of the road and this will affect the signal or can give a different reading on oscilloscope.
Wheel speed sensor can be checked with two things, an oscilloscope or multimeter, but oscilloscope will be more accurate in finding faults!
