Wheel Speed Sensor

 "A poor girl wants to marry, and a rich girl wants to flirt."

"A rich man goes to college, and a poor man goes to work."

- Charlie Daniels (Long-Haired Country Boy)

 No stoic quote today, just a great observation about society by Charlie Daniels (RIP).

A while back, after our daughter had completed her driver's education course, she got a car.  She used most of her savings, and we helped her with the rest, so that she would not have to get a loan - the car was pretty inexpensive.  She has great taste in cars - it's a Mercedes.  I don't think I owned that nice of a car until I was in my 40's, haha.

All I cared about was that it was All-Wheel Drive and crash-worthy - which of course it's both.  Most people don't like these cars, because repair parts are expensive.  Fortunately, you no longer have to buy repair parts from the dealer, so the notion that they are expensive to repair is not exactly correct.   You can buy a Chinese knock-off part for 1/10 the price.  If you have to replace it 9 times, you are still money ahead.

The ABS (Anti-Lock Brake System) warning light in the kid's car has been coming on the for the past week or so.  Last weekend, I finally had time to connect up the code reader to the car and see what's up with it.  I haven't had the code reader for very long, but it's already saved me several hundred dollars in repair bills.  I highly recommend owning one of these so that dealerships don't try to bamboozle you.

 I connected the code reader up to her car, and it came back with a "Driver's Side Front Wheel Speed" error.  I didn't bother with further troubleshooting.  It could have been a bad connection or wire, and it could have been a bad "reluctor ring" - also known as a "tone ring".  Instead I ordered a new wheel speed sensor, and hoped that was the problem.

 Below: ABS mechanism.  The teeth on the reluctor ring pass by the wheel speed sensor, and each time a tooth goes by, it generates a small electrical pulse in the sensor.  The sensor sends a constant series of pulses to the ABS computer that correspond to wheel speed.  Once a tire locks up under hard braking, the ABS will release the brakes slightly on that one wheel.  The most effective braking occurs just before total wheel lock-up.  During a panic stop, the ABS computer modulates brake pressure on each wheel to maintain a little bit of rotation - which is determined by the pulses sent by the wheel speed sensor.  

The ABS computer will generate an error code (and turn on the ABS light on the dash) if the vehicle is moving, but the computer receives no pulses from a wheel speed sensor. 

I drove the kid's car into the shop, removed the front driver side wheel, and took a look.  Nothing looked obviously wrong.  The shiny black cable is the new wheel speed sensor.  It replaced the thicker black cable running off the image to the top.  The tiny white wire seems to be a brake pad wear monitor.

This isn't hard to do, folks.  I simply removed the old sensor, one tie-down point at a time.  I installed the new one as I removed each section of the old one, so that there was no chance of error or not routing the new one correctly.  The connection to the wiring harness was up under the hood, underneath the windshield washer fluid reservoir.  That part was a bit difficult to disconnect and reconnect, but I got it done without damaging any wiring. 

Afterwards I re-installed the wheel and took it for a spin.  Lo-and-behold, no more warning light on the dash!!!

Price for this repair (not including the earlier purchase of the code reader):  $21 bucks.  This likely would have cost several hundred dollars at a Mercedes dealer, and probably 200-300 dollars at Joe's garage.

One place where I was unable to save money was new tires.  They were pretty worn when we bought the car, and recently during a rain-storm they were a bit scary.  Pretty worn in the middle.

A set of four of these arrived yesterday, but I've not had the time to get them mounted yet.  Supposedly they provide good winter traction.  I'll be sure and mention in a future post whether that's true or not after trying them out this winter.