Basically there are two sensors in the throttle. They are 0-5 volt so at idle one reads 0 and the other reads 5 volts. As the throttle is moved each sensor voltages changes but added together they will = 5 volts.
So if one of the sensors runs wild it throws a code. Are you sure the wire were inserted correctly? Like 5 volt and sensor return crossed?
By chance did you do any adjusting on the sensor end plastic piece that meshes with the grip if so may have thrown off the calibration?
Thanks Brad. Just got a printout of the P2138 diagnostic procedure from Jim after he checked in to offer a hand also. May be a few days now before we get back to it so will gladly bank any insights collected in the interim.
The two sides of the sensor aren't crossed. Have checked and double checked. The OE harness wrap covers internal wraps that separate each trio of wires. One trio with a yellow internal wrap and one trio with (if I remember correctly) a white wrap. Nothing crossed there.
Brian (Hogasm) also mentioned in a phone call this morning that he's seen an instance of the TGS housing itself shorting against the handlebar. With an accurate low voltage meter I'm getting nothing when measuring at the bars. So no leakage nor short from the TGS housing itself nor the wires.
Jim mentioned this morning that some of these throttle grip sensors have a harness that includes a small connector that is easily damaged. I didn't think this sensor had that connector. But a call and email from yet another site watcher made it clear I could be mistaken there. Was sent a picture showing an exploded view of that version of the sensor and the micro-connector was shown to be inside the harness wrap that is pulled through the handlebars. It could be there and I would have missed it as it would've been out of sight and I'd not have known to look.
In that same message I was told the TGS with the small and delicate connector is 32310-08 and that a different version of the TGS that is more robust and does not include the small connector in mid-harness is 32305-08A. Should later effort end up showing, despite the bike seeming to run ok, that the grip sensor is the problem what I'd also like to confirm is that the two versions of the grip sensor are interchangeable.