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I would start with the plug on the back of the indicator. They will get corroded and corrosion can cause PFM problems with low power digital circuits. This is what mine looked like when I was doing the restoration. The plug on the indicator was worse.
On my 2003 FLHTCUI, any problems with the engine system sensors or system voltage sensed by the ECM will trip a fail code which will shut down the bike until the codes are cleared. I have experienced this happening twice. I replaced the battery the first time and I could not find any reason for the second failure. I saw the voltage erratic on the gauge and it ran crappy and tripped a fail code when I shut down. Both times I got the red key icon in the speedometer and I had to clear the codes to ride on.
Thanks for all the replies. Still no luck. What I want to try now, if it’s possible is to somehow hookup a voltmeter to the speed sensor so I can test it while I ride. On demand, about 30 minutes into a ride the bike mirrors symptoms of a failed speed sensor despite it being new. I need to know if there is a change in output from the sensor when the badness starts. It will rule something internal out if the speed sensor functions normally and allow me to hunt down step-by-step where the signal loss occurs. I need to just start testing every connection speed sensor to speedometer as I ride to see where the variation exists, but I’m not sure how to go about accomplishing this.
Thanks for all the replies. Still no luck. What I want to try now, if its possible is to somehow hookup a voltmeter to the speed sensor so I can test it while I ride. On demand, about 30 minutes into a ride the bike mirrors symptoms of a failed speed sensor despite it being new. I need to know if there is a change in output from the sensor when the badness starts. It will rule something internal out if the speed sensor functions normally and allow me to hunt down step-by-step where the signal loss occurs. I need to just start testing every connection speed sensor to speedometer as I ride to see where the variation exists, but Im not sure how to go about accomplishing this.
A very basic static electrical test you could do is to look at the connector itself for the speed sensor. Check for terminal tightness at the terminals, perform a wiggle test at the harness. Make sure that the terminal spades are not wallowed out and causing loss of connection while riding. Wiggle test meaning that the wire is properly seated into the connector. Also, check the ground side circuit, make sure you are not having a loose grounding bolt, which can always lead to strange electrical concerns.
In tapping into the wire to measure output, you want to make sure you are not causing more damage to the harness. Meaning if you cut into the wires to a fix your test leads, make sure to do a proper wiring repair afterwards. A speed sensor typically will measure using AC voltage.
You need to check your codes and run speedometer diagnostics test procedures outlined in your manual. That should have been the first thing you did after checking connections. If you don't have a manual, then get one. Good luck.
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