05 FLHTCI speedometer problem

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I been working on this bike for a friend. Got the gas gauge working I think.
He had problem with speedo not working right also and a couple other problems.
Speedo works but is not reading right. Seems to when going up through gears but varies when cruising, bouncing up and down about 20 mph. He replaced speed sensor and speedo. I checked wire connections and grounds. Found a code for TSM and reset it.  My electrical manual is for 02 (my bike). I found some differences in 05 speedo and 02 speedo.

Not sure what to check for now. Any suggestions?

[Hossamania]

Pull the new speed sensor and check it for debris?

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Checked speed sensor, replaced sensor, replaced speedo but still have problem. Need a look at electrical manual for test procedures.

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Checking codes through speedo I get a code U1255 serial data error. I have been tracing wires for continuty but haven't found anything yet. Rode bike about 15 miles speedo sways about 20 mph while steady cruising. The turn signals cancel like they should, one of the tings I found that was not right. Checked codes and got U1255 after reset before ride.

I am looking  for what is causing this code and how to cure it. Checking all connections again.

[Hossamania]

Just for fun, using a voltage meter, what is the battery voltage when at rest, and while running?

[Coyote]

Could be the wiring or could be the TSM/TSSM or could be the ECM. But I would suspect it to be an issue with communications from the ECM to the Speedo. Might try unplugging and reseating the ECM connector.

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Went through all the connectors and trace wire from speed sensor through harness. Found sensor signal wire that goes through ECM, TSM, Cruise control to speedo and tach was rubbed on a brace inside fairing from from main harness. Relocated the connector and repaired wire. Bike started and did not throw a code. When it stops raining I will take a test ride.

[fleetmechanic]

I once threw away a good speedo from a 2002 FLHTP and later found it was the wiring by the frame neck.  Have seen it a couple of other times since.