Speed Sensor--Clean or Replace?
Road Master
Joined: Dec 2007
Posts: 878
Likes: 0
From: Tellico Plains, Tenn.
Had the speed sensor on my RG act up after about 155k. Lost speed indication & trip/odometer. Followed the shop manual procedures for pulling up the speedo codes. The sensor was being faulted. Changed the sensor & all seemed well until about 4 miles into a road test. Lost all speedo functions including backlighting. Thinkin WTF????? Pulled the speedo/tach & found the connector had come unplugged. Oops! Didn't plug in the connector all the way. Secured the connector & works like a charm now.
Ride Safe Ya'll! The only cure for my disease is 2 knees in the breeze!
Ride Safe Ya'll! The only cure for my disease is 2 knees in the breeze!
5th Gear
Joined: Jul 2010
Posts: 9
Likes: 1
From: Norway
You are of course sure about the colors after re-installing the wires? They shall of cource mach the colors in the other plug. Just a thought.
Cruiser
Joined: Jan 2008
Posts: 173
Likes: 1
From: New York
Does any one have a picture of the vehicle speed sensor from the magnet side. I have a theory which might answer whether to change or clean the sensor.
Typically the speed sensors I am familiar with are magnets with very fine wire wound around them. The magnets are engineered to mount at a very close and very precise distance away from the teeth of the gear they are monitoring. The magnetic lines of flux emanating from the magnet are affected by the ferrous teeth of the gear passing through the lines of flux causing a calculable change in flux density. As a result of this flux density change, a voltage is induced into the wire surrounding the magnet. This voltage is an AC voltage with a frequency that is directly proportionate to the speed of rotation of the gear. Thus it forms a readable signal for the speedo to decode. I'm pretty sure this is the way HD has engineered the VSS.
Now the theory part. In my thirty years of trouble shooting rail road Speed Control and Wheel Slip Systems, which use the above type of speed sensors, I found that if the resistance reading of the sensor wiring was within specs, the failure occurred from the epoxy mounting the magnet failing and the magnet moving to engage the gear. This wipes out the fine wiring and blows away the sensor. A visual inspection of the magnet when it's new should either reveal tool marks from manufacture or no marks at all. If you see any marks that look like lines across the face of the magnet it is as a result of the magnet engaging the gear teeth and the sensor needs to be replaced even if it looks otherwise pristine.
Having said that, if I were paying for the labor to remove the sensor and the bike wasn't covered by warrantee I'd replace the sensor no matter what it looked like.
Just my opinion
Typically the speed sensors I am familiar with are magnets with very fine wire wound around them. The magnets are engineered to mount at a very close and very precise distance away from the teeth of the gear they are monitoring. The magnetic lines of flux emanating from the magnet are affected by the ferrous teeth of the gear passing through the lines of flux causing a calculable change in flux density. As a result of this flux density change, a voltage is induced into the wire surrounding the magnet. This voltage is an AC voltage with a frequency that is directly proportionate to the speed of rotation of the gear. Thus it forms a readable signal for the speedo to decode. I'm pretty sure this is the way HD has engineered the VSS.
Now the theory part. In my thirty years of trouble shooting rail road Speed Control and Wheel Slip Systems, which use the above type of speed sensors, I found that if the resistance reading of the sensor wiring was within specs, the failure occurred from the epoxy mounting the magnet failing and the magnet moving to engage the gear. This wipes out the fine wiring and blows away the sensor. A visual inspection of the magnet when it's new should either reveal tool marks from manufacture or no marks at all. If you see any marks that look like lines across the face of the magnet it is as a result of the magnet engaging the gear teeth and the sensor needs to be replaced even if it looks otherwise pristine.
Having said that, if I were paying for the labor to remove the sensor and the bike wasn't covered by warrantee I'd replace the sensor no matter what it looked like.
Just my opinion
5th Gear
Joined: Jul 2010
Posts: 9
Likes: 1
From: Norway
Artt:
Wery interesting information about the speed sensor. This tells me there is no easy way to check if the sensor is ok or not. You will have to have an advanced piece of equipment that has the same software as the speedo.
I have attached a picture of my sensor.
Wery interesting information about the speed sensor. This tells me there is no easy way to check if the sensor is ok or not. You will have to have an advanced piece of equipment that has the same software as the speedo.
I have attached a picture of my sensor.
Cruiser
Joined: Jan 2008
Posts: 173
Likes: 1
From: New York
It's difficult to see in the picture but it does look like there is some wear from contact on the magnet.
You don't need special equipment to check the sensor, just a VOM on resistance. If the resistance is lower or higher than the specs on a new sensor it's either shorted or opening up and incapable of generating the necessary voltage range required for the electronics to read. You should be able to read the resistance at the plug on the sensor without removing the sensor just disconnect the sensor from the circuit. Only 2 problems 1, you need to know the correct spec and the service manual doesn't specify what that is and 2, if it is within spec you still have to remove the sensor to clean the metal filings that may be interfering with the signal generation.
You don't need special equipment to check the sensor, just a VOM on resistance. If the resistance is lower or higher than the specs on a new sensor it's either shorted or opening up and incapable of generating the necessary voltage range required for the electronics to read. You should be able to read the resistance at the plug on the sensor without removing the sensor just disconnect the sensor from the circuit. Only 2 problems 1, you need to know the correct spec and the service manual doesn't specify what that is and 2, if it is within spec you still have to remove the sensor to clean the metal filings that may be interfering with the signal generation.
5th Gear
Joined: Jul 2010
Posts: 9
Likes: 1
From: Norway
Ok artt.
You need to explain to me. I know there is a permanent magnet in the sensor. I could feel that with a screwdriver when the plug was disconnected. Now, there are three wires to the sensor. According to the electrical drawing there are 12V DC as supply, and the third wire is the feedback. How does this work? Is the 12V going to the magnet?
Also, explain to me the phrase "VOM on resistance" I quess you are talking about an instrument capable of meassuring very small Ohm`s? Where to meassure? Between the 12V and 0 pins, or between the 12V and sensor pin, or between 0 and sensor pin?
Thank you for explaining.
I know the easiest thing is to just change the sensor and see what happens, but the discussion is interesting.
You need to explain to me. I know there is a permanent magnet in the sensor. I could feel that with a screwdriver when the plug was disconnected. Now, there are three wires to the sensor. According to the electrical drawing there are 12V DC as supply, and the third wire is the feedback. How does this work? Is the 12V going to the magnet?
Also, explain to me the phrase "VOM on resistance" I quess you are talking about an instrument capable of meassuring very small Ohm`s? Where to meassure? Between the 12V and 0 pins, or between the 12V and sensor pin, or between 0 and sensor pin?
Thank you for explaining.
I know the easiest thing is to just change the sensor and see what happens, but the discussion is interesting.
Tourer
Joined: Feb 2008
Posts: 251
Likes: 4
From: Philadelphia
Hi all,
This sounds like an old post, but I'm having power loss interruption on the speedo of my 2000 Dyna. I've looked at everything except replacing this speedometer speed sensor.
At key on, my speedo is fine. It quits totally...odometer blanks out....about 5 sec after engine start.
The weird thing is that if I select left or right signal switch, the odometer flashes back on and off in sequence with signal lights....!!
Anyone seen or experienced this?
Jim
This sounds like an old post, but I'm having power loss interruption on the speedo of my 2000 Dyna. I've looked at everything except replacing this speedometer speed sensor.
At key on, my speedo is fine. It quits totally...odometer blanks out....about 5 sec after engine start.
The weird thing is that if I select left or right signal switch, the odometer flashes back on and off in sequence with signal lights....!!
Anyone seen or experienced this?
Jim
Last edited by jim70; Mar 24, 2014 at 01:42 AM.
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Stage II
Joined: Sep 2016
Posts: 2
Likes: 0
From: shallotte nc
Speed sensor 2001 ultra classic
Yep...did the same thing when I replaced mine....much easier to route the wire if I ever have to replace it again.