Speed Sensor Faults!
People from the Volkswagen club are all too familiar with this issue and I know it drives a lot of folks crazy! And people usually meet me for the first time due to this little sensor's fault. So maybe it's a great time for me to discuss about this little part that causes so much anxiety with most folks.
1. What is this so called ABS /SPEED Sensor?
It's a small sensor usually located behind the brake caliper area/wheel bearing area. Its purpose as the name implies is to read out speed. It gives the computer of the car a read out of the speed of the wheels of the car. For Volkswagen, there is usually 4 speed sensors, one for each wheel. This sensors are made of magnets that give a certain voltage reading to the ECU whenever a gear/magnet on the wheel bearing passes it.
2. What is an indication that you have a Speed sensor problem?
Christmas lights! (that's the common joke) But usually it will trigger the driver gauge cluster to light up so many different error/indicator lights. But the most certain one is the ABS light. Why to so many lights light up when the ABS sensors fail? That is because the ABS sensor is actually used as basis for so many different modules by the vehicle. For the Jetta for example, it is used by the ABS module, Steering wheel module (to calculate how hard, soft the steering wheel is based on speed), Traction Control (it will deactivate the TCS since it lack's speed information) and the Tire Pressure Light (since tire pressure is calculated by comparing the speed of all 4 tires to detect for variance). For other cars, more light will probably light up since the Speed sensor is basis for so many modules in the vehicle.
But do take note. it's not only speed sensors that may cause these errors on the dashboard. A broken wheel bearing, faulty wiring and even a faulty ABS module may cause these errors on the dash. So have the mechanic check it first before doing any replacement.
3. Is it bad to drive the car with a faulty ABS sensor?
Yes and No. Well Yes because if your ABS is lit up, it means the car has deactivated your ABS system. So doing high speed braking may cause your car to skid and lock up on the brakes. So this means one safety feature is deactivated. But VW has actually prevented getting this problem by actually limiting your car. This is what people usually refer to as LIMP MODE. The system will actually limit you from using full speed/power so that you wont get into a tricky unsafe situation.
Is it bad to use the car? Well not really, using the car on a prolonged period wont do any harm on the engine. But do take note, it is going to be a hassle using a slow car on the road. So have them changed asap for your sanity.
4. Why do they fail?
Honestly I don't have a proven main reason why. But these may fail due to wear and tear, weather conditions, heat factors, magnets failing, and internal wiring of the sensors failing. So is there a good sign that will tell me when they will fail? Nope! Honestly it's a hit or miss. I know some folks who have never changed sensors even if the car is already 5 years old. and I know some who's lucky enough to get one broken sensor every month once one of them starts freaking out.
5. Should I change them all?
It would really depend on the owner. But usually if the client lives far away in the rural areas without access to a diagnostic computer tool, I would recommend changing all 4 once one acts up. But if the customer lives nearby my area and is easily able to visit the shop, it's ok to replace just what's at fault. Are our ABS sensors expensive? Not really. we're lucky because some Japanese brands and Korean brands cost way more than ours and they also fail prematurely as well. So at the end of the day, it's really the client's call if they would want to change all of them.
6. What sensors should I get?
Here at the shop we usually recommend the ones that are proven to be of good quality. We also get feedback from our suppliers abroad which ones are good to offer our clients. And we also offer 1 year warranty for the ABS sensors incase they die on you prematurely (but honestly we have very little claims even after 2-3 years)
7. I've seen some cheap speed sensors from that shopping site, are they good?
Please don't buy those! yes they may be very inexpensive, but do take note that these little sensors are connected to the ABS module and that module is a very expensive part to replace! So a SHORTED CHEAP speed sensor may give you bigger problems in the future.
Anyways, It's been a very lengthy Blog post for me. I hope I have enlightened the readers about the nature of ABS/Speed sensors. Hopefully understanding them will cause less stress for our clients. So next time the dash lights up like a Christmas tree, well... have the car scanned here at the shop. We'll scan them for free. Hopefully it's just a faulty small speed sensor.
Have a great day! Drive safe!
-Ed