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I have a 2004 Honda Rubicon 500 with Hondamatic and all time 4x4. It has had a easy life belonging to my grandfather-in-law. After his passing it sat for 5 years. Now his great-grandchildren are old enough to ride so we pulled it out and found it has an issue. We first found it would not shift at all flashing the D1 D2 and ESP and noticed it didn't show any speed when rode. After some research and testing I found there was no power to speed sensor. I jump a hot to the speed sensor and everything started working. After approximately 30 minutes of riding it would stop shifting and start flashing the D1 D2 and ESP again. Pulled the codes and get a code 4. Check voltage to throttle position sensor and get 5.1 to the hot side and variable voltage as you move the throttle on the sensor wire. I check the resistance between the ground and variable on the throttle position sensor and got 40ish. I read the it is suppose to be close to 500. I did some talk to the widow that actually owns the machine and she stated that the machine actually started doing this before her husband died and that he took it to a Honda shop and they told him it need a new computer which I am guessing she meant ECM and not the display which is what feeds the power to the speed sensor. I have tried clearing the code and doing the initialization procedure no change.

I guess my real question is where should I go from here? Is there a way to test the ECM so I know that is issue vs the throttle position sensor?

Any help will be much appreciated. Please explain things like like you are talking to a 5th grader i run into burning buildings and not a mechanic 😆
 

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The speed sensor probably should get 5V, not 12V. So your jumper wire should be to the Pink/Green wire.
You could replace the TPS, but if the voltage varies from 0.5-5V, it should be good, unless the voltage is dropping too low and causing the computer to throw the code 4. Try starting and running it with the throttle pressed slightly all the time.
 
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