ABS Speed sensor


#1

2006 Honda CR-V 4 WD. L F wheel speed sensor. Daughters car. ABS light came on. Codes for LF sensor came up. Inspection showed that bracket came loose. Sensor wire was damaged. Replaced with a “Standard” brand sensor. Test drove and abs light stayed on. Put scanner on it and got mph readings on all wheels except LF. Been 12 hours fixing deer collision damage so I let her take car home out of town till I could test some other time. Tested new sensor today. No A.C. voltage when turning wheel and ohm check reads open. I ordered a new standard sensor that is the same as the bad one because I don’t have original box. That way I can use box to replace bad sensor for warranty. Got the new sensor and did a real quick ohm test. There were numbers so I assumed it was good. Installed new sensor and it failed also. No A.C. current when spinning and reads 25.5 M ohms. Does anyone know what ohms these sensors are supposed to have? The tone generator for these things are inside the wheel bearing. Bearing is good. Either I’m missing something here or I need to get another new sensor of a different brand. Honda dealership wants $225 for one. HHaving hard time spending that much. Others are $70 - $140.


#2

The wheel sensor will produce an ac waveform output when

  • it is a good part & getting power & ground (it is a solid state device)
  • it is spaced 0.5 - 1.5 mm from the encoder
  • the encoder is turning along w/the wheel

So you got something wrong with one of those. It looks like you have to remove the driveshaft to measure the spacing. I don’t see a spec for the resistance between its two pins, but you could measure the resistance on the working sensor at the other side of the car. Note that the resistance may vary depending on how you place the meter’s + or - leads; i.e. the sensor is polarized.

Note to measure resistance you have to disconnect the sensor first. Only measure resistance on the sensor itself, not with it connected to anything.

There’s only two pins and one is connected to ground from what I see. So another idea is to measure the voltage between those two pins on a known good sensor compared to what you’re seeing on the faulty one. The pin that gets the power to power the sensor also is the pin which outputs the ac waveform based on the diagrams I’m seeing. I’m guessing you may have a ground problem going on. This test should show that up, if that’s the problem.


#3

Time restraints kept me from comparing ohms with other side. Plus I didn’t even think of it. Thanks for that tip. When I get the car again next week end I will compare ohms. I think it is safe to put the tone generator at the bottom of the list of problems because it is in the bearing. If the ohm test passes, I’ll remove axle and check sensor gap. This sensor produces no A.C.current when wheel spins.


#4

I have a feeling this is a digital sensor, not analog


#5

Your right. I assumed it was passive because it only has 2 wires. But I just did a quick search and it appears that the magnetic field source is in the bearing. That means that there should be constant voltage in one of the wires. I’ll also check for voltage on working sensor


#6

Ohmmeter readings don’t tell you much when you are testing active devices such as this.


#7

Yeah, thought it was passive, I’m now trying to find a wiring diagram with no luck. The original sensor wires were damaged. Didn’t think much of it when I thought it was passive. Now I’m concerned that electrical damage may have occurred as this is a powered system


#8

so damaged wire caused an issue upstream? where does the abs sensor wire go?


#9

Not sure if damage is upstream yet. Still looking for diagram. I might have to purchase one this afternoon. I assume the sensor goes to module, but I think I need diagram to do anything productive.


#10

you got a new sensor but it is not honda oem. others are 70-140. what did you pay for your new one. i assumed you got a nonhonda sensor in the 70-140 range?


#11

Paid$138 for Standard brand sensor aftermarket. When I get car back this Saturday, I will check circuit. I now have a diagram. Very easy to test if circuit is good I’ll bite the bullet for $225 OEM sensor.


#12

To understand how the sensor works, consider this analogy: Hang a weight from a pole using a spring. Choose a spring so the weight hangs 4 feet off the ground. Every time a cute girl goes by, a helper pulls the weight to the ground momentarily and lets go. The weight returns to the original height b/c of the spring. You can watch from a distance how much bouncing of the weight is going on to determine the frequency of cute girls going by.

The two pins on your sensor correspond (1) to the weight, and (2) to the ground. So the only one which has a constant voltage is the ground. Unless there are no cute girls going by (i.e the wheel is not spinning), and then the weight has a constant voltage (height).


#13

This system is an active 2 wire system. There is supposed to be battery voltage at all times with key on on supply wire. The other wire is the signal wire. It returns voltages in a square wave pattern. When wheel is turning, I should see voltage ranging from .6 to 1.2 volts. My initial mistake was that I thought this was a passive sensor. You can check a passive sensor using ohm meter. You cannot check active sensor that way. The old sensor had bare wire showing. That would not be anything to worry about on a passive system, but an active system has battery voltage and it could have shorted something. I also noted when I found my diagram that on Hondas and a few other models that if you unplug the sensor, the module shuts down the reference voltage to the sensor. So I have to backprobe to test. My concern now is if I don’t find voltage at the sensor or at the LFPij at the VSA module I’ll probably have to replace module. I don’t know yet, but the diagram does not show separate circuits for each sensor. On Saturday I’ll know more when I get the car and do some voltage tests


#14

Interesting afternoon with the CRV. Got battery voltage at sensor on the positive side and got .03 volts on signal wire. So far so good. At the module, I got battery voltage on the positive wire and didn’t check the signal wire yet. I cleaned the bearing where the tone generator is, and took it on test drive. I was convinced the second sensor was bad. I then thought to make sure that the signal wire was good. I back probed both wires at module and got close to 12 volts. Did the same on sensor side and got 5 volts. So I have voltage drop. So I cut signal wire at sensor connector and module connector and temperarily put new wire inn between. My scanner originally read LF sensor failure and LF sensor voltage high or low. After I put the temporary jumper wire in, the high or low voltage fault disappeared but the sensor failure fault is still there. Now I’m convinced that I have both a bad sensor and a bad signal wire. The funny thing is though that after I removed the temporary jumper from signal wire which left the signal wire completely open, I expected the high or low voltage fault to come back and it didn’t. I ran out of time, now I have to wait till next time to finish. I’m thinking that replacing signal wire and putting in an OEM sensor should fix it.


#15

I got the car in again Saturday. I ran new wires from the sensor connectors to the module the $140 sensor still did not work so I opened the $240 OEM sensor and put it in. Didn’t work. Retested voltage from module to module side of speed sensor. Good. Retested voltage from module to sensor side of connector and was bad. When I jiggled connector it would let voltage through intermittently. Because I didn’t do a jiggle test the first time I checked it, cost me $240. I bypassed connector and all is well.


#16

i am thinking of buying this new ACTRON Brand #CP9449 ABS Scan Tool. it is unused but i think it is for older cars. perhaps 2000-2006 era like my equinox. which has an abs issue. though i think the abs issue is typical for these equinoxes. maybe it will work? my kid has a similar age saturn vue with an abs light. so kill 2 birds with one stone?


#17

I am now using Actron CP 9580. I also had an older one. On Actrons website you can hook your scanner to your computer and update the scanner for free. It’s a very good scanner for non commercial.


#18

Why didn’t you just replace the pigtail, versus bypassing it?


#19

That would have been best, but with daughter living out of town, I couldn’t get a pigtail in time for her to go home.