2016 TRX500FA7 Honda Rubicon, Mil light comes on when downshifting from 4th to 3rd gear.

[Sha35297]

I have this bike in my shop for a customer. It was sunk completely under water and left running until it killed. I did a complete engine rebuild. Replaced all bearings, crank, oil pump, and various other components. Engine starts and runs great. It will shift up through all gears perfectly in automatic and in ESP, but when slowing down it gets to 3rd gear and the MIL "-" light comes on and stays on. No flashes or anything and it will not shift gears. Kill the engine and restart in ESP mode and it is able to shift to neutral and start over. Does the same thing while down shifting in ESP mode. I replaced shift angle sensor with no improvement. Checked oil pressures as per repair manual "74psi" and higher with higher RPM's. With no MIL codes to point at an issue. I am at a loss as to what else to check or replace. Has anyone else ran across this issue?

[Gwbarm]

A MIL (Malfunction Indicator Lamp) code on a Honda Rubicon indicates a problem detected by the vehicle's onboard diagnostics system. Common issues can include sensor failures or electrical problems. If it was dunked i would suspect a sensor connection problem and if the ECM got wet maybe shorted.

[Sha35297]

Gwbarm, Yes I know what the MIL light is. That is why I stated that it is not blinking to indicate a code. It is just staying on solid and there are no codes stored in the ECM. I am a mechanic who works on these daily. I have followed all of the troubleshooting tips in the service manual with no help. Just trying to see if anyone has had this issue before or maybe could steer me in a direction that I may be over looking. Thanks.

[Sha35297]

Update, I read on another forum that these bikes are prone to having the, Gearshift Return Spring Pin, break off. So I drained fluids and removed the font crank case cover to put my eyes on that pin. It was not broken and was doing its job. so I reassembled everything. Added fluids and tested again. Same issue as before. I also cleaned the idle air control valve, TPS, and speed sensors. I pulled every electrical plug and cleaned them with electrical cleaner and blew them out. Nothing has made any changes in the behavior. I notice that if I downshift manually in ESP mode while still slightly holding the throttle it will sometimes work better. Never in Automatic mode though. So I may replace the TPS to see if it will resolve the issue. Still no trouble codes either. 

[Sha35297]

Final update on this issue. The shift pin in my previous post was not the issue in this case. After replacing every electronic component on the ATV with no change with the problem. I had to pull the engine back off completely and go through everything with a fine tooth comb. Finally I found an issue that is not mentioned anywhere in the manual, on the internet that I can fine, NOWHERE. Inside the main shaft that the dual clutch goes on there is a brass or copper ring that the feed pipe "A" stabs into. In my case that brass/copper ring was scarred up. Apparently causing a variation in the oil pressure that the computer sensed and made it now allow the bike to down shift. It never threw an actual code. The MIL light comes on steady and does not allow the bike to shift at all. I installed a new mainshaft and now the bike shifts great. I hope this helps anyone who has this issue.