Can somebody explain wheel speed sensors to me

I'd put money on corrosion in the sensor plug. If you disconnect it and look very closely you may see the green tinge of electrical death. We're talking ohms here, doesn't take hardly anything to disrupt that sensor reading to the computer. If you have that just replace the whole sensor. Mix up some baking soda and water to pour in the harness plug. If you find a tiny drill bit you can use that to clean the insides of the plug sockets. Use dielectric grease on the plug when you go back together. Depending on the age of the unit I would suggest this treatment on all of your sensor plugs.

 

Check the plug under the dash. Might still be corrosion, just on the opposite end

 

Keep tracing wires back to the Wabco in cab ecu. Don’t know about yours, but mine in 2000 Freightliner is mounted under the bunk, behind passenger seat. Has a plastic louvered cover. It has a diagnostic switch on the side. Hig the switch and count the dash flash codes for diagnosis. Wires go from sensors to ecu on frame. More wires from frame to main ecu in cab. Usually in sections. Need to find the break in wire, if any. As far as I know the sensor itself is just a magnet. No sensitive electronics. They can’t go bad. Wire May break right at the sensor , and sensor needs replaced. Best to be clean, but works fine even if full of grease, and oil. Because it’s a magnetic signal, needs to be right against the tone ring. No need to set a gap, just push sensor up against tone ring. Rust and being bent as mentioned will affect reading. Your question about getting wires crossed??? Yes it’s possible, more so an issue on trailers. Depending which way it’s facing. Code could describe left or right wheels. Trucks nit do much. Mines mounted as mentioned under front of fifth wheel, on cross frame bracket. Wires from right side wheels, go to right side of ecu, quick release valve is also mounted on right side of ecu, for right side wheels, left side of ecu is the same way, wires, air valve, air lines for left wheel’s mounted on left side of ecu. I had to dig into the wires going from ecu towards in cab control module. Had a diagnosis from flash code, followed the wire, replacing a section at a time, using a new wire. A 8 or 10 ft wire is good, long enough. Mine has 2 between frame ecu and cab module. First wire from ecu was bad. Replaced with new, tested using flash code, bundle up excess wire, issue fixed. So start at wheel, work back towards cab. Had another issue and had to replace the ecu on frame. They sell them separately and as a combo unit, with new air valves mounted.

 

Because your unloading the suspension, making the tone ring come out of round just enough to loose the magnetic signal.

Jack up the axle, put a dial indicator up against the tone ring, and rotate by hand, you'll see the variance.

Don't go chasing wiring issues. I wasted a month chasing wiring think that, my tone ring was off by like 2 thousands..

 

What were your codes?
These 3 indicate wiring issues.
2 4 RF circuit shorted to ground
2 5 RF wheel sensor circuit open
2 6 RF wheel sensor sensor wires shorted together

An out of round tone ring could act like missing teeth as they are not picked up by the sensor.
2 7 RF tone ring missing or incorrect number of teeth

Ohms is an unreliable way to test. Ohms can be in spec but the sensor is bad. There are other threads on here about that. The best way is to use an oscilloscope to check the waveform of the sensor but many shops won't have one of those or know how to use it. So for many that leaves the ac volts test.

 

I can't remember the codes.

DDDL Software told me which wheel position it was. In my case case RR axle, position 6.

Bought a new sensor from dealer (250$), changed it my self, no change, still christmas tree, and no fix.

Ohme'd out the harness from the axle to the CPC, cleaned connections, drove, still no change.

Got fed up and took it to dealer, they laughed at me for driving with my foot on the pedal for a month, we'll fix it.

In and out in 6 hours for 700$. Tone ring out of balance, pull the wheels, brakes, Hub, replace Tone ring (50$), clean all surfaces, reassemble, test.

#### happens in trucking.

My brother (Master ASME Certified VW, Audi, BMW mechanic) was once #####ing about how much painters were gonna charge to repaint his vaunted staircase in his million dollar home.

I said how much, he said 1500 for 2 days work, I can do it for 300 in paint.

I said, you can make 4000 in one day working on cars, spend the next day watching people work for you. Let the professionals handle painting, while you do the professional jobs.